703
Effects of Diuretics on Inner Medullary Hemodynamics
in the Dog
Samuel Spitalewitz, Shyan-Yih Chou, Pierre F. Faubert, and Jerome G. Porush
From the Division of Nephrology and Hypertension, Department of Medicine, The Brookdale Hospital Medical Center, Brooklyn,
New York
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
SUMMARY. Although the hemodynamic effects of diuretics have been studied extensively, their
effects on inner medullary blood flow remain unknown. In the present study, renal hemodynamics,
including papillary plasma flow measured by the albumin accumulation technique, and associated
alterations in papillary tissue solute content were determined in anesthetized, hydropenic dogs and
during euvolemic diuresis induced by furosemide (3 mg/kg plus 2 mg/kg per hr, iv), ethacrynic acid
(3 mg/kg plus 2 mg/kg per hr, iv) or chlorothiazide (10 mg/kg plus 10 mg/kg per hr, iv). Renal
blood flow increased significantly after furosemide and ethacrynic acid and decreased significantly
after chlorothiazide. Sixty minutes after diuretic administration, papillary plasma flow was 10.8 ±
1.0 (mean ± SE) in six furosemide- and 11.3 ± 2.6 ml/min per 100 g in six ethacrynic acid-treated
dogs, both significantly lower than in eight normal or eight chlorothiazide-treated dogs [26.4 ± 2.6
and 26.7 ± 2.7 ml/min per 100 g, respectively (P < 0.01)]. A similarly low papillary plasma flow was
also noted 10 minutes after diuretic administration in five furosemide and four ethacrynic acid dogs
(13.6 ± 2.3 and 13.4 ± 1.8 ml/min per 100 g, respectively). In furosemide and ethacrynic acid dogs,
papillary osmolaliry and sodium content were significantly lower than those in normal or chlorothiazide dogs. In normal and chlorothiazide dogs, papillary sodium content was similar, with a
significantly reduced papillary osmolality in the latter. At the time papillary plasma flow was
measured, extracellular fluid volume was similar among the four groups of dogs; however, plasma
renin activity increased significantly in furosemide and ethacrynic acid dogs (P < 0.01) and remained
unchanged in normal and chlorothiazide dogs. Furthermore, papillary plasma flow was restored to
normal (25.3 ± 3.9 ml/min per 100 g) in five dogs in which furosemide was infused during
angiotensin II blockage with saralasin, despite a similar diuresis and natriuresis as the other
furosemide group. These data demonstrate that after administration of furosemide, ethacrynic acid
and chlorothiazide, regulation of papillary plasma flow is independent of renal blood flow, and
suggest that angiotensin II may play a role in the reduced papillary plasma flow in furosemide and
ethacrynic acid dogs. (Circ Res 51: 703-710, 1982)
THE renal hemodynamic effects of various diuretics
have been extensively investigated. After the administration of the loop diuretics, furosemide and ethacrynic acid, renal vascular resistance decreases and
renal blood flow (RBF) increases accompanied by
renal renin release (Ludens et al., 1968; Vander and
Carlson, 1969; Freeman et al., 1974; Corsini et al.,
1975). It has been suggested recently that the increase
in RBF elicited by these diuretics is, in part, mediated
by increased renal production of prostaglandin E
(Williamson et al., 1975, 1976; Patak et al., 1979;
Gerber and Nies, 1980). Thus, the increase in RBF
after the administration of loop diuretics occurs in the
presence of stimulation of two vasoactive systems in
the kidney, the renin-angiotensin and prostaglandin
systems. On the other hand, chlorothiazide, which is
known to decrease RBF, has no significant effect on
renal renin or prostaglandin release (Brown et al.,
1966; Cooke et al., 1970; Patak et al., 1979).
Alterations in intracortical blood flow distribution
after the administration of various diuretics have been
studied in detail with the radioactive microsphere
(McNay and Abe, 1970; Stein et al., 1972) and inert
gas washout methods (Birtch et al., 1967). However,
the effects of diuretics on inner medullary blood flow
have not been examined and should be of considerable interest in view of ample evidence for a stimulatory effect of endogenous prostaglandins on renal
medullary circulation (see review by Stokes, 1981).
The present study was designed to examine the effects
of furosemide, ethacrynic acid, and chlorothiazide on
papillary plasma flow (PPF) and papillary solute content during the maintenance of a constant extracellular
fluid volume in the dog. The data are interesting in
that the loop diuretics caused an increase in RBF but
a marked decrease in PPF, associated with an increase
in plasma renin activity (PRA). In contrast, chlorothiazide caused a decrease in RBF with no change in
PPF or PRA. In addition, when furosemide was infused during angiotensin II blockade with saralasin
PPF did not decrease.
Methods
All experiments were performed on female mongrel dogs
maintained on a daily diet containing 60 mEq of sodium
and 40 mEq of potassium and allowed free access to water.
The animals were placed in metabolic cages for a period of
5 days prior to the acute studies, during which period a
704
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
careful record of sodium, potassium, and water balance was
kept. Acute studies were performed after it was demonstrated that the animals were in sodium balance.
For the acute experiment, food was withdrawn at 4:00
p.m. the day before, but water was permitted up to the
morning of the experiment. The dogs were anesthetized
with sodium pentobarbital, 30 mg/kg, iv. Light anesthesia
was maintained with supplemental doses given throughout
the experiment, as necessary. An endotracheal tube was
inserted and the urinary bladder was catheterized with a
Foley catheter. To ensure accurate determination of urine
volume, double air washouts were used to empty the bladder completely during clearance periods. Blood samples
were obtained and mean arterial blood pressure (MAP) was
monitored through a catheter inserted into the left femoral
artery, advanced to the level just below the left renal artery.
A catheter was placed in a femoral vein for infusing solutions.
Through a flank incision, the left kidney was exposed
and the renal pedicle gently dissected to expose the renal
artery fully. An electromagnetic flow probe (model 400
series, Carolina Medical Electronics) was placed around the
artery and total RBF measured with an electromagnetic
flowmeter (model 322, Carolina Medical Electronics). After
the probe was in place, an umbilical tape was passed around
the renal pedicle and a loose knot tied. Zero flow was
determined by brief occlusion of the renal artery distal to
the probe. The flow probe was calibrated by in situ perfusion of the renal artery at the conclusion of the experiment.
After initial blood and urine samples were obtained, a
priming dose of inulin was administered, followed by a
sustaining solution of 0.9% NaCl containing sufficient inulin
to maintain adequate blood levels, infused at 50 ml/hr with
a constant rate infusion pump.
After a 60-minute equilibration period, three 10-minute
urine specimens were collected with midpoint blood samples for clearance determinations. A blood specimen was
then obtained for the measurement of PRA, hematocrit, and
plasma total protein. Four groups of dogs were studied.
Group I, consisting of eight dogs weighing 25.2 ± 1.3 kg
(mean ± SEM), served as the control; these dogs were observed for an additional 60 minutes. In group II, six dogs
weighing 22.8 ± 1.5 kg received an intravenous loading
dose of 3 mg/kg of furosemide, followed by 2 mg/kg per
hr added to the constant infusion. In group 111, six dogs
weighing 12.5 ± 1.5 kg received a loading dose of 3 mg/kg
of ethacrynic acid followed by 2 mg/kg per hr added to the
constant infusion. In group IV, eight dogs weighing 23.1 ±
1.0 kg received a loading dose of 10 mg/kg of chlorothiazide
followed by 10 mg/kg per hr added to the constant infusion.
After a 30-minute equilibration period following the administration of the diuretics or vehicle solution alone in the
normal dogs (nondiuretic treated), three 10-minute clearance periods were obtained. A blood sample was again
obtained for determination of PRA, hematocrit, and plasma
total protein. After a diuresis commenced, intravenous replacement was begun with a solution containing 135 mEq/
liter Na+, 123 mEq/liter Cl", 10 mEq/liter K+, and 22 mEq/
liter HCCV. This replacement solution was infused at a
rate of 0.8 ml/min less than the urinary flow rate. At the
end of clearance and hemodynamic measurements, PPF was
determined by the method of radioactive albumin accumulation originally described by Lillienfield et al. (1961)
with the modifications described in our previous report
(Faubert et al., 1982). Briefly, 125I-albumin, 100 juCi/ml
(Mallinckrodt, Inc.), with a small amount of cardiogreen
dye, was infused by a reciprocal action pump (Harvard
Circulation Research/Vo/. 51, No. 6, December 1982
Apparatus Co., Inc.) at a rate of 4 /tCi/sec through the
catheter placed in the femoral vein. When the cardiogreen
dye appeared in the aorta at the level of the renal artery,
detected by a densitometer (model DTL, Gilson Medical
Electronics) connected to the aortic catheter, blood was
withdrawn from the same catheter through a 3-way stopcock arrangement using the reciprocal action pump and
exactly matching the infusion of 125I-albumin. After a simultaneous perfusion and collection period of 12 seconds,
the umbilical tape knot around the left renal pedicle was
pulled tight and the blood collection stopped at the same
time. The kidney was removed immediately and frozen at
—10°C for 20 minutes. The papilla was cut, weighed, and
counted, together with an aliquot of plasma. PPF was calculated according to the formula:
PPF (ml/min per 100 g)
_ cpm/100 g papilla
60
cpm/ml plasma
perfusion time (sec)
An additional nine dogs were studied exactly as described
above, except that PPF was determined at the end of 10
minutes of furosemide infusion in 5 dogs and 10 minutes of
ethacrynic acid infusion in four dogs.
An additional five dogs (three undergoing furosemide
and two undergoing ethacrynic acid diuresis) were studied
exactly as described above, except that the simultaneous
perfusion of l25I-albumin and collection of arterial blood
were terminated at 20 seconds.
Because PRA increased significantly with the loop diuretics (see below), the effect of furosemide on PPF was also
studied during angiotensin II (All) blockade with saralasin
in five dogs. After a 60-minute equilibration period, saralasin was infused at 2 /ig/kg per min, iv, and continued
throughout the experiment. Thirty minutes after saralasin
administration, furosemide infusion was initiated as described above for 60 minutes and PPF determined. Fluid
replacement was carried out as described for the other
diuretic groups.
Papillary osmolality, sodium, and water content were
determined using the methods previously described from
this laboratory (Faubert et al., 1982). Inulin was determined
on an Autoanalyzer (Technicon Instruments Corp.), and
sodium and potassium by standard flame photometry. Total
plasma protein was analyzed by the Biuret method (Gornall
et al., 1949) and PRA was determined by radioimmunoassay
as previously described (Flombaum et al., 1978). Clearances
were calculated by standard methods.
Statistical Analysis
All results are expressed as mean ± SEM. Student's t-test
was used for paired and unpaired data. To assess statistical
significance between groups, a one-way analysis of variance
was performed using Scheffe's test for comparisons when
F values were significant. P < 0.05 was considered statistically significant.
Results
The effects of diuretics on urine flow rate, electrolyte excretion, systemic and renal hemodynamics are
summarized in Table 1. The control values represent
the mean of the steady state clearance periods, and
the experimental values represent the mean of three
10-minute periods 30-60 minutes after the administration of the vehicle solution in group I and the
Spitalewitz et al./Diuretics and Medullary Hemodynamics
705
TABLE 1
Urine Volume and Osmolality, Plasma and Urine Electrolytes, Renal and Systemic Hemodynamics in Normal and Diuretic Treated
Dogs
PN.
Uosm
V
(ml/min)
(mOsm/kg
H 2 O)
FE Na
(%)
UN»V
fyiEq/min)
(mEq/liUKV
PK
ter)
(^Eq/min) (mEq/liter)
C ta
(ml/min)
RBF
(ml/min)
MAP
(mm
Hg)
Normal
(n =8)
0.46 0.46 1,300 1,267 53 62
±0.07 ±0.08 ±144 ±151 ±15 ±19
Furosemide
(n = 6)
0.30 12.1* 1,431
±0.05 ±1.2 ±109
323* 31 1,715* 0.3 16.2* 150 150 52 226* 3.7 3.5 71 70 224 255* 128 124
±7. ±8 ±173 ±0.1 ±1.5 ±2 ±2 ±12 ±30 ±0.1 ±0.1 ±4 ±3. ±19 ±20 ±8 ±10
Ethacrynic
acid (n = 6)
0.21 12.9* 1,362
±0.04 ±1.8 ±75
315* 291,931* 0.4 25.8* 148 148 46 211* 4.1 4.0 54 56 173 267* 120 119
±9 ±8 ±182 ±0.1 ±3.9 ±1 ±1 ±5 ±15 ±0.2 ±0.2 ±5 ±4 ±24 ±28 ±7 ±6
Chlorothiazide
(n =8)
0.42- 3.2* 1,435 679* 42 583* 0.3 4.9* 147 145 52 148* 3.7 3.6 97 82f 211 196f 130 129
±0.05 ±0.4 ±82 ±30 ±13 ±66 +0.1 ±0.8 ±1" ±1 -.-.> ±7 ±23 ±0.1 ±0.1 ±11 ±7 ±16 ±17 ±6 ±7
0.5 0.5 147 147 45 48
±0.1 ±0.2 ±2 ±2 ±5 ±8
3.8 3.9 80 83 199 200i 137 139
±0.1 ±0.1 ±10 +10 ±21 ±21 ±6 ±5
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
V = urine volume, U^m = urinary osmolality, UNOV = absolute urinary sodium excretion, FE Na = fractional sodium excretion, PN8 =
plasma sodium concentration, UKV = absolute urinary potassium excretion, PK = plasma potassium concentration, Cin = inulin clearance,
RBF = renal blood flow, MAP = mean arterial pressure, C = control, E = experimental.
* P < 0.01 compared with control values.
f P < 0.05 compared with control values.
diuretics in the other three groups. During the control
period, urine flow and sodium excretion were similar
among the four groups. The increase in urine volume
after furosemide or ethacrynic acid was approximately 4-fold that after chlorothiazide administration.
Fractional sodium excretion increased from 0.3 ± 0.1
to 16.2 ± 1.5% after furosemide, from 0.4 ± 0.1 to
25.8 ± 3.9% after ethacrynic acid, and from 0.3 ± 0.1
to 4.9 ± 0.8% after chlorothiazide administration. RBF
increased significantly after furosemide and ethacrynic acid (from 224 ± 19 to 255 ± 20 ml/min and
from 173 ± 24 to 267 ± 28 ml/min, respectively) and
decreased significantly after chlorothiazide (from 211
± 16 to 196 ± 17 ml/min). Plasma sodium and
potassium concentration were similar in all four
groups during control and did not change significantly
during the experimental period.
The results of the arterial blood hematocrit, total
plasma protein, and PRA during control and experi-
mental periods are summarized in Table 2. A similar
hematocrit and total plasma protein were noted
among the four groups during the control period and
remained unchanged during the experimental period,
suggesting similar extracellular fluid volume among
the four groups during the control and experimental
periods. PRA was similar among the four groups
during the control period and did not change during
the experimental period in normal or chlorothiazide
treated dogs. A significant increase in PRA occurred
after furosemide and ethacrynic acid administration
(from 4.4 ± 1.1 to 10.1 ± 1.3 ng/ml per min and from
4.5 ± 0.8 to 10.6 ± 1.4 ng/ml per min, respectively).
The results of PPF in normal and diuretic treated
dogs are shown in Figure 1. In chlorothiazide dogs,
PPF was 26.7 ±2.7 ml/min per 100 g, similar to that
in normal dogs (26.4 ± 2.6 ml/min per 100 g). PPF in
furosemide and ethacrynic acid dogs was 10.8 ± 1.0
and 11.3 ± 2.6 ml/min per 100 g, respectively, sig-
TABLE 2
Hematocrit, Total Plasma Protein, and Plasma Renin Activity in Normal and Diuretic-Treated Dogs
Hematocrit
Total plasma protein
(g/dl)
PRA
(ng/ml per hr)
Normal (n = 8)
39 + 1 39 ± 1
5.90 + 0.20
5.90 ± 0.20
5.1 ± 1.0
4.5 + 0.5
Furosemide (n = 6)
42 + 2 43 ± 2
5.51 + 0.32
5.39 + 0.24
4.4 ± 1.1
10.1 ± 1.3*
Ethacrynic acid (n = 6)
39 + 1 40 ± 1
6.10 ± 0.23
5.92 ± 0.14
4.5 ± 0.8
10.6 ± 1.4*
Chlorothiazide (n = 8)
39 + 1 40 ± 2
6.02 ± 0.41
5.94 ± 0.39
3.8 ± 1.3
5.2 + 1.5
PRA = plasma renin activity, C = control, E = experimental.
* P < 0.01 compared with control values.
706
Circulation Research/Vo/. 51, No. 6, December 1982
5
or
* P< O.Ol
O) 4 0
—
O
o
o
"^ 3 0
o
o
I
ll
o
JO.
20
I-
O
o
o
a.
10
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
o *—
N
EA
CTZ
FIGURE 1. Papillary plasma flow (PPF) in norma/ dogs (N) and 60
minutes after the administration of furosemide (F), ethacrynic acid
(EA), and chlorothiazide (CTZ). Asterisk, P < 0.01 compared with
normal or CTZ dogs.
tissue water content was not significantly different
among the four groups. In the furosemide and ethacrynic acid dogs, papillary osmolality was significantly lower than that in normal or chlorothiazide
dogs, approaching isotonicity. Papillary sodium content was also significantly reduced when compared to
normal or chlorothiazide dogs. In the chlorothiazide
group, papillary osmolality was lower and papillary
sodium content was similar compared to normal dogs.
Table 5 summarizes the effects of furosemide on
renal function and PPF during All blockade with
saralasin. Hematocrit and total plasma protein were
40 ± 1% and 5.89 ± 0.10 g/dl, respectively, and
remained unchanged during the experimental period.
When compared with the dogs given furosemide
alone (group II), there was a similar increase in urine
volume, sodium, and potassium excretion. As in
group II, GFR and MAP were not significantly
changed; however, the increase in RBF was significantly greater. PPF was 25.3 ± 3.9 ml/min per 100 g,
significantly greater than in dogs treated with furosemide alone and indistinguishable from that of normal dogs (Table 3, Figure 1). Papillary tip tissue water
content was 89.4 ± 0.4%, osmolality was 327 ± 12
mOsm/kg H2O, and sodium content was 90 ± 2
mmol/100 g dry solids, similar to that of group II
(Table 4).
Discussion
nificantly lower than normal or chlorothiazide dogs
(P < 0.01). Since PPF was derived from the volume of
distribution (Vt) of 125I-albumin at 12 seconds (an
index of the quantity of the radioactive marker accumulating in the papilla via descending vasa recta
relative to that in the arterial plasma), it was necessary
to ascertain that the significantly reduced PPF after
furosemide or ethacrynic acid was not due to a substantial loss of the marker through ascending vasa
recta at the time of testing (12 seconds). For this
reason, the Vt was also determined at 20 seconds in
dogs treated with furosemide and ethacrynic acid. A
progressive rise was noted in Vt (Fig. 2), suggesting
that it is unlikely that a significant amount of the
marker was leaving the papilla at 12 seconds.
Although PPF was low 60 minutes after the administration of the loop diuretics, it is possible that a
decrease in PPF was preceded by an early increase
after the loop diuretics were infused. PPF was, therefore, also measured 10 minutes after the administration of furosemide and ethacrynic acid and was again
significantly lower in these animals compared with
normal dogs (Table 3), at a time when renal blood
flow was already significantly above baseline values
(Table 3). PRA increased significantly from 4.8 ± 1.5
to 8.7 ± 1.7 ng/ml per hr 10 minutes after furosemide
and from 4.1 ± 0.7 to 10.6 ± 1.1 ng/ml per hr 10
minutes after ethacrynic acid administration (P <
0.01).
Table 4 summarizes the results of papillary tip
tissue water content, osmolality, and sodium content
obtained when PPF was measured at 60 minutes. Wet
In the present study, we have examined renal hemodynamic responses to furosemide, ethacrynic acid,
and chlorothiazide when a constant extracellular fluid
volume is maintained. Total RBF significantly increased after the administration of the two loop diuretics and decreased after chlorothiazide. In contrast,
a disparate response was noted in inner medullary
hemodynamics. PPF was markedly reduced after fu-
o
X
(0
H
<o 4
ox
0)
o
X
X
3
o
O
1
t~iff
o
2
o
1
0
—
X
1
1
1
1
1
8
12
16
20
1
24
28
Time (second)
FIGURE 2. Volume of distribution (V,) at 12 and 20 seconds 60
minutes after the administration of furosemide (O) and ethacrynic
acid (X). The brackets indicate the mean ± SEM for the diuretics
combined at each time interval.
Spitalewitz et a/./Diuretics and Medullary Hemodynamics
707
TABLE 3
Papillary Plasma Flow and Percent Change in Renal Blood Flow after Furosemide and Ethacrynic
Acid Administration
Furosemide
PPF (ml/min per 100 g)
Ethacrynic acid
Normal
10 min
60 min
10 min
60 min
(n =8)
26.4 ± 2.6
(n = 5)
13.6 ± 2.3*
(n =6)
10.8 ± 1.0*
(n = 4)
13.4 ± 1.8*
(n = 6)
11.3 ± 2.6*
Change in renal blood
flow above baseline
14 ±6t
24 ± 10f
14 ±
54 ±
PPF = papillary plasma flow. •
* P < 0.01 compared with normal dogs.
t P < 0.05, $ P < 0.01.
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
rosemide and ethacrynic acid administration and similar to normal dogs after chlorothiazide. PRA increased with the two loop diuretics but was not
significantly changed with chlorothiazide.
Since furosemide and ethacrynic acid caused an
immediate increase in RBF and PPF was decreased 60
minutes after the infusion of the two diuretics, it was
possible that PPF could have been increased initially
and then decreased. Therefore, PPF was measured 10
minutes after the diuretic infusion and was found to
be significantly reduced and accompanied by a significant rise in PRA (similar to 60 minutes) (Table 3).
The low PPF following loop diuretic administration
was not the result of volume contraction or hypokalemia (Whinnery and Kunau, 1979), since both factors
were carefully maintained constant (Table 1 and 2).
The administration of furosemide and ethacrynic
acid resulted in a marked reduction in papillary solute
concentration, approaching isotonicity, whereas chlorothiazide caused a smaller decrease in papillary osmolality. The effects of altered extracellular osmolality on vascular resistance should, therefore, be considered. For example, the markedly diminished interstitial osmolality after the loop diuretics might lead to
medullary vascular cell swelling and thereby contribute to the suppressed PPF. However, a number of
studies have demonstrated an elevated PPF in the
presence of markedly reduced papillary osmolality
and a low PPF in a highly concentrated papilla. Buerkert et al. (1978) have shown that papillary solute
content was severely depressed during acute unilat-
eral ureteral obstruction, yet PPF increased remarkably in response to the release of ureteral obstruction.
Chuang et al. (1978) observed an elevated PPF in
water diuresis compared to hydropenia, and demonstrated that exposure of the renal papilla during water
diuresis, a situation in which papillary tonicity was
already markedly reduced, further increased PPF. In
models of chronic salt retention, we have found a
markedly depressed PPF during hydropenia accompanied by a substantial increase in papillary tissue
osmolality (Spitalewitz et al., 1980, Faubert et al.,
1982). Moreover, furosemide superimposed on saralasin restored PPF to normal, although papillary osmolality was greatly decreased and similar to dogs
given furosemide only. Thus, it seems unlikely that
the low PPF after loop diuretics is specifically related
to changes in papillary solute content induced by the
diuretics.
Recent studies have provided evidence suggesting
that medullary prostaglandin production may increase inner medullary blood flow. Chuang et al.
(1978) demonstrated that inhibitors of prostaglandin
synthesis lowered PPF in the exposed papilla of Munich-Wistar rats. Solez et al. (1974) reported that the
reduction in PPF after indomethacin correlated with
a decrease in circulating levels of prostaglandins A
and E in the rat. Using a video velocity tracking
system, Jamison et al. (1981) observed that prostaglandin inhibition decreased erythrocyte velocity in
the vasa recta of the rat papilla. It has been shown
that furosemide and ethacrynic acid cause an increase
TABLE 4
Papillary Tip Tissue Osmolality, Water, and Sodium Content in Normal Dogs and 60 Minutes after
the Administration of Diuretics
Normal (n = 8)
Furosemide (n = 6)
Ethacrynic acid (n = 6)
Chlorothiazide (n = 8)
Osmolality
(mOsm/kg H2O)
H2O Content
1005 ± 52
381 ± 34*
363 ± 10*
695 ± 49f
86.8 ±
87.0 ±
88.4 ±
87.5 ±
(%)
Na Content
(mmol/100 g dry solids)
0.6
0.9
0.6
0.4
* P < 0.01 compared with normal or chlorothiazide-treated dogs.
t P < 0.01 compared with normal, furosemide or ethacrynic acid-treated dogs.
152 ± 4
87 ±6*
75 ±4*
131 ± 5
Circulation Research/Vo/. 51, No. 6, December 1982
708
TABLE 5
Effect of Furosemide on Renal Function during Saralasin Administration Compared with Croup II
V
(ml/min)
Furosemide
with
saralasin (n = 5)
UN-V
(/lEq/min)
321*
±7
-1019
±231
±65
±228
-1109
±104
1684
±173
NS
NS
NS
0.6
1340
21
±71
E
±0.1
11.1*
±1.9
±9
1393*
A'
10.5
±1.9
11.8
±1.3
NS
FENa
(%)
0.23
±0.04
14.98*
±2.68
14.75
±2.57
15.9
±1.4
C
A
Group II (furosemide alone) (n =
6)
P value (A vs. A')
Uo5m
(mOsm
/kg
H2O)
1373
UKV
C,n
RBF
OiEq/min)
(ml/min)
(ml/min)
67
MAP
(mm Hg)
81
±24
177
±12
131
±4
288*
68
250*
123
±4
±5
-1
±18
77
±14
31
±3
±5
±63
254
±69
175
±20
NS
1
±2
NS
<0.01
PPF
(ml/min
per 100 g)
±6
25.3f
±3.9
-8
±4
-4
±4
NS
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
Abbreviations: see Table 1.
A, difference between E and C.
A', difference between E and C in group II shown in Table 1.
* P < 0.01 compared with control values.
t P < 0.01 compared with papillary plasma flow in group II (10.8 ± 1.0 ml/min per 100 g).
in urinary excretion of prostaglandin E, whereas chlorothiazide fails to do so (Patak et al., 1979). If the loop
diuretics enhanced medullary prostaglandin E production in the present experiments, it was not associated with an increase in PPF as anticipated. In fact,
we found the opposite effect. The explanation for this
discrepancy may be related to activation of the reninangiotensin system observed as early as 10 minutes
after the infusion of the loop diuretics in the present
experiments. In this regard, we have also previously
observed a low PPF in chronic salt-retaining caval
dogs (Faubert et al., 1982) and chronic salt-depleted
dogs (Spitalewitz et al., 1980), both of which were
associated with a markedly elevated PRA. The observation that PPF did not decrease when furosemide
was administered during All inhibition with saralasin
(Table 5), strongly supports the proposal that activation of the renin-angiotensin system is the cause of
the low PPF with loop diuretics. In line with this
suggestion is the fact that the demonstration of an
effect of prostaglandins on medullary blood flow has
been indirect via use of prostaglandin synthesis inhibitors in experiments in which the renin-angiotensin
system was not stimulated (Solez et al., 1974; Chuang
et al., 1978; Jamison et al., 1981).
The distribution of cortical blood flow during the
administration of various diuretics has been analyzed
previously by the radioactive microsphere method.
McNay and Abe (1970) demonstrated that ethacrynic
acid augmented blood flow to the two midcortical
zones with unchanged blood flow to the juxtamedullary cortex. Stein et al. (1972) also obtained a similar
result with furosemide and observed that chlorothiazide decreased total RBF without appreciable alteration in the fractional intracortical blood flow distribution. Thus, the blood flow distribution to the juxtamedullary cortex determined by the microsphere
method does not correlate with our measurement of
PPF after these diuretics. We have previously dem-
onstrated the lack of correlation between cortical
blood flow distribution and PPF in models of chronic
salt retention. In chronic caval dogs with avid salt
retention, a marked reduction in PPF was not associated with an alteration in cortical blood flow distribution during either hydropenia or saline loading
(Faubert et al., 1982). A similar observation was also
made in dogs with chronic salt depletion in which a
low PPF was not accompanied by a reduction in inner
cortical blood flow (Spitalewitz et al., 1980). These
findings may be explained by the fact that microspheres measure glomerular blood flow only, which
may not reflect changes in the post-glomerular capillary circulation of juxtamedullary nephrons.
Anatomical studies of the medullary vasculature in
the dog are consistent with this view (Barger and
Herd, 1973; Beeukes and Bonventre, 1975). The efferent arterioles derived from the juxtamedullary glomeruli either divide immediately into a convoluted
capillary plexus or divide into a sheaf of vasa recta at
a varying distance from their glomeruli. The former
does not perfuse the inner medulla and the latter runs
through the outer medulla with small branching twigs.
Most vasa recta terminate at the junction of the outer
and inner medulla by breaking up into a dense capillary network, and only the central vessels of the vasa
recta bundle perfuse the papilla. Accordingly, blood
flow to juxtamedullary glomeruli is partitioned among
inner cortex, outer and inner medulla in unknown
proportions. In addition, ultrastructural studies demonstrate the presence of smooth muscle cells in the
juxtamedullary glomerular efferent arterioles and
vasa recta. Along the descending vasa recta the encircling smooth muscle cells are gradually replaced by
pericytes, cells containing filaments possibly capable
of contractile function (Moffat, 1967; Chou et al.,
1981). Thus, it is conceivable that inner medullary
blood flow is regulated separately from juxtamedullary glomerular blood flow. Furthermore, this ana-
Spitalewitz et aJ./Diuretics and Medullary Hemodynamics
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
tomical arrangement could allow for the effects of
vasoactive substances (angiotensin II or prostaglandins) on PPF without a significant change in overall
RBF or juxtamedullary glomerular blood flow. In fact,
we have recently observed a significant decrease in
PPF after intrarenal angiotensin II infusion without a
concurrent decrease in RBF (unpublished observation).
The effects of various diuretics on the cortico-medullary solute gradients have been studied extensively,
and our results of papillary tissue content after the
diuretics are consistent with previous reports (Hook
and Williamson, 1965; Goldberg, 1966). In addition
to the direct effect of a pharmacological agent on
tubular solute transport, alterations in medullary hemodynamics could affect the solute content of the
medullary interstitium and urinary concentration
(Earley and Friedler, 1965; Lameire et al., 1980). After
chlorothiazide administration, PPF was similar to that
of normal dogs, despite a significant fall in total RBF.
This finding supports the original suggestion by Earley et al. (1961) that the effects of chlorothiazide on
urinary dilution and concentration are due to a single
action of this agent on the renal tubule.
The ability of the two loop diuretics, furosemide
and ethacrynic acid, to abolish the cortico-medullary
solute gradient has been attributed primarily to a
direct action on salt reabsorption by the thick ascending limb of Henle's loop. A secondary effect on
medullary solute due to an increase in RBF and an
associated increase in medullary blood flow by these
agents could further enhance their effect on the concentrating mechanism (Stowe and Hook, 1970) and,
possibly, the natriuresis. A washout of medullary
solute due to an increase in inner medullary blood
flow is not supported by the present study, however.
In addition, when PPF was restored to normal by
saralasin, furosemide did not induce a greater diuresis
and natriuresis, further suggesting that the major
action is due to a direct effect on loop salt transport.
It is of interest to note that prostaglandin F2a, an
agent that appears to inhibit salt reabsorption by the
thick ascending limb of Henle's loop, also dissipates
medullary solute, almost to isotonicity, without altering PPF in dogs (Zook and Strandhoy, 1981). This
agent, however, may also inhibit vasopressin-mediated water and urea reabsorption (Zook and Strandhoy, 1980; Roman and Lechene, 1981). Although
furosemide and ethacrynic acid increase renal prostaglandin E production (Williamson et al., 1975,1976;
Patak et al., 1979), the site(s) of production is not clear
and whether the produced prostaglandins affect tubular urea movement (Roman and Lechene, 1981) or
collecting tubule vasopressin-dependent hydro-osmotic water flow (Grantham and Orloff, 1968) remains to be studied.
We acknowledge the technical assistance of Richard Byrd, Kenneth Salsman, and Vita Israel, and the secretarial assistance of
Pauline Kleiman and Pauline Wemick.
709
Furosemide used in this study was kindly supplied by HoechstRoussel Pharmaceuticals Inc., Somerville, New Jersey.
This work was done during S. Spitalewitz's tenure as a fellow of
the National Kidney Foundation. Portions of this work were presented at the 54th Scientific Sessions of the American Heart Association, Dallas, Texas, Nov., 1981.
This work was supported by National Institutes of Health Grant
HL-26281 and New York State Health Research Council Grant K073.
Address for reprints: Jerome G. Porush, M.D., Chief, Division
of Nephrology and Hypertension, The Brookdale Hospital Medical
Center, Linden Boulevard at Brookdale Plaza, Brooklyn, New York
11212.
Received: January 28, 1982; accepted for publication September
9, 1982.
References
Barger AC, Herd JA (1973) Renal vascular anatomy and distribution
of blood flow. In Handbook of Physiology. Renal Physiology,
edited by J Orloff, RW Berliner. Washington, DC, American
Physiological Society, pp 249-313
Beeukes R, Bonventre JV (1975) Tubular organization and vascular
tubular relationship in the dog kidney. Am J Physiol 229:695-713
Birtch AG, Zakheim RM, Jones LG, Barger AC (1967) Redistribution of renal blood flow produced by furosemide and ethacrynic
acid. Circ Res 21: 869-878
Brown TC, DAvis JO, Johnston CI (1966) Acute response in plasma
renin and aldosterone secretion to diuretics. Am J Physiol 211:
437-441
Buerkert J, Martin D, Head M, Prasad J, Klahr 5 (1978) Deep
nephron function after release of acute unilateral ureteral obstruction in the young rat. J Clin Invest 62: 1228-1239
Chou SY, Park IY, Faubert PF, Porush JG (1981) infrastructure of
canine medullary vessels: Hemodynamic implications (abstr).
Proc Am Soc Nephrol 14: 116A
Chuang EL, Reineck HJ, Osgood RW, Kunau RT Jr, Stein JH (1978)
Studies on the mechanism of reduced urinary osmolality after
exposure of the renal papilla. J Clin Invest 61: 633-639
Cooke CR, Brown TC, Zacherle BJ, Walker WG (1970) The effect
of altered sodium concentration in the distal nephron segments
on renin release. J Clin Invest 49: 1630-1638
Corsini WA, Hook JB, Bailie MD (1975) Control of renin secretion
in the dog: Effects of furosemide on the vascular and macula
densa receptors. Circ Res 37: 464-470
Earley LE, Friedler RM (1965) Studies on the mechanism of natriuresis accompanying increased renal blood flow and its role in
the renal response to extracellular volume expansion. J Clin
Invest 44: 1857-1865
Earley LE, Kahn M, Orloff J (1961) The effects of infusions of
chlorothiazide on urinary dilution and concentration in the dog.
J Clin Invest 40: 857-866
Faubert PF, Chou SY, Porush JG, Belizon IJ, Spitalewitz S (1982)
Papillary plasma flow and tissue osmolality in chronic caval
dogs. Am J Physiol 242: F370-F378
Flombaum CD, Chou SY, Porush JG, Slater PA, Ferder LF, Levin
DL, Gadhok RS (1978) Serial evaluation of the renin-angiotensinaldosterone system in caval dogs. Circ Res 42: 778-786
Freeman RH, Davis DO, Gotshall RW, Johnson JA, Spielman WS
(1974) The signal perceived by the macula densa during changes
in renin release. Circ Res 35: 307-315
Gerber JG, Nies AS (1980) Furosemide-induced vasodilation: importance of the state of hydration and filtration. Kidney Int 18:
454-459
Goldberg M (1966) Ethacrynic acid: Site and mode of action. Ann
NY Acad Sci 139: 443-459
Gornall AG, Bardawill CJ, David MM (1949) Determination of
serum protein by means of biuret reaction. J Biol Chem 177:
751-766
Grantham JJ, Orloff J (1968) Effect of prostaglandin Ei on the
permeability response of the isolated collecting tubule to vasopressin, adenosine 3',5'-monophosphate, and theophylline. J Clin
Invest 47: 1154-1161
710
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
Hook JB, Williamson HE (1965) Effect of furosemide on renal
medullary sodium gradient. Proc Soc Exp Biol Med 118: 372-374
Jamison RL, Gussis G, Lemley K, Robertson C (1981) Studies of
the effects of antidiuretic hormone and prostaglandin inhibition
on RBC velocity in vasa recta of the inner renal medulla. Proc Int
Cong Nephrol Athens 8: 170-175
Lameire N, Vanholder R, Ringoir S, Leusen I (1980) Role of
medullary hemodynamics in the natriuresis of drug-induced
renal vasodilitation in the rat. Circ Res 47: 839-844
Lilienfield LS, Maganzini HC, Bauer MH (1961) Blood flow in the
renal medulla. Circ Res 9: 614-617
Ludens JH, Hook JB, Brody MJ, Williamson HE (1968) Enhancement of renal blood flow by furosemide. J Pharmacol Exp Ther
163: 456-460
McNay JL, Abe Y (1970) Redistribution of cortical blood flow
during renal vasodilitation in dogs. Circ Res 1023-1032
Moffat DM (1967) The fine structure of the blood vessels of the
renal medulla with particular reference to the control of the
medullary circulation. J Ultrastruct Res 19: 532-545
Patak RV, Fadem SZ, Rosenblatt SG, Lifschitz MD, Stein JH (1979)
Diuretic-induced changes in renal blood flow and prostaglandin
E excretion in the dog. Am J Physiol 236: F496-F500
Roman RJ, Lechene C (1981) Prostaglandin E2 and F^ reduces urea
reabsorption. Am J Physiol 241: F53-F60
Solez K, Fox JA, Miller M, Heptinstall RH (1974) Effects of indomethacin on renal inner medullary plasma flow. Prostaglandins
7: 91-98
Spitalewitz S, Chou SY, Faubert PF, Pourush JG (1980) Effects of
chronic salt depletion on intracortical blood flow distribution
and papillary plasma flow in the dog (abstr). Clin Res 28: 462A
Circulation Research/Vo/. 51, No. 6, December 1982
Stein JH, Mauk RC, Boonjarern S, Ferris TF (1972) Difference in
the effect of furosemide and chlorothiazide on the distribution
of renal cortical blood flow in the dog. J Lab Clin Med 79:
995-1003
Stokes JB (1981) Integrated actions of renal medullary prostaglandins in the control of water excretion. Am J Physiol 240:
F471-F480
Stowe NT, Hook JB (1970) Role of hemodynamic changes in the
effect of furosemide on the renal concentrating mechanism. Eur
J Pharmacol 9: 246-252
Vander AJ, Carlson J (1969) Mechanism of the effects of furosemide
on renin secretion in anesthetized dogs. Circ Res 25: 145-152
Williamson HE, Bourland WA, Marchand GR, Farley DB, Van
Orden DE (1975) Furosemide induced release of prostaglandin
E to increase renal blood flow. Proc Soc Exp Biol Med 150:
104-106
Williamson HE, Marchand GR, Bourland WA, Farley DB, Van
Orden DE (1976) Ethacrynic acid induced release of prostaglandin E to increase renal blood flow. Prostaglandins 11: 519-522
Zook TE, Strandhoy JW (1980) Inhibition of vasopressin-induced
urea flux in toad urinary bladder by prostaglandin E2 and prostaglandin Fzu. Prostaglandins 20: 1-13
Zook TE, Strandhoy JW (1981) Mechanisms of the natriuretic and
diuretic effects of prostaglandin F^. J Pharmacol Exp Ther 217:
674-680
INDEX TERMS: Diuretics • Papillary plasma
nin-angiotensin • Angiotensin II blockade
flow
Re-
Effects of diuretics on inner medullary hemodynamics in the dog.
S Spitalewitz, S Y Chou, P F Faubert and J G Porush
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
Circ Res. 1982;51:703-710
doi: 10.1161/01.RES.51.6.703
Circulation Research is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 1982 American Heart Association, Inc. All rights reserved.
Print ISSN: 0009-7330. Online ISSN: 1524-4571
The online version of this article, along with updated information and services, is located on the
World Wide Web at:
http://circres.ahajournals.org/content/51/6/703
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in
Circulation Research can be obtained via RightsLink, a service of the Copyright Clearance Center, not the
Editorial Office. Once the online version of the published article for which permission is being requested is
located, click Request Permissions in the middle column of the Web page under Services. Further information
about this process is available in the Permissions and Rights Question and Answer document.
Reprints: Information about reprints can be found online at:
http://www.lww.com/reprints
Subscriptions: Information about subscribing to Circulation Research is online at:
http://circres.ahajournals.org//subscriptions/