313s
Clinical Science (1982) 63,313.3-317s
Interaction of the sympathetic nervous system with
vasopressin and renin in the maintenance of blood pressure
in rats
P E T E R H A T Z I N I K O L A O U , I R E N E G A V R A S , W I L L I A M G. N O R T H ,
HANS R. BRUNNER AND HARALAMBOS GAVRAS
Thorndike Memorial Laboratories, Boston City Hospital, and Department of Medicine. Boston University Medical School,
Boston, MA, and the Department of Physiology, Darimouth Medical School, Hanover, NH,U S A .
Summary
1. Anephric and intact rats were submitted sequentially to catecholamine depletion
(‘chemical sympathectomy’) vasopressin inhibition and angiotensin blockade whilst blood
pressure and plasma levels of each hormone were
monitored.
2. Depletion of catecholamines to 15-25% of
baseline levels was associated with significant fall
of blood pressure. A close correlation existed
between these variables.
3. Chemical sympathectomy caused stimulation of plasma vasopressin, which reached excessively high levels in anephric animals. These
were inversely correlated with the levels of
depleted catecholamines.
4. Vasopressin inhibition after chemical sympatliectomy caused profound and lasting hypotension in anephric rats but only a transient small
fall in blood pressure in intact rats. Angiotensin
blockade after chemical sympathectomy in intact
rats caused a transient small fall in blood
pressure; subsequent vasopressin inhibition in
these rats caused profound lasting hypotension.
5. It is concluded that resting blood pressure is
mainly sustained by the sympathetic nervous
system, whereas renin and vasopressin are
important back-up mechanisms to maintain
compromised blood pressure.
Introduction
Normal blood pressure is maintained by the
equilibrium of a number of vasoactive mechanisms, including the sympathetic nervous system,
Correspondence: Dr H. Gavras, 80 E. Concord
Street, Boston, M A 021 18, U.S.A.
the renin-angiotensin system and vasopressin.
The present experiments were designed to evaluate the contribution of these three vasopressor
systems to the maintenance of blood pressure at
rest and after elimination of each one of these
systems in sequence.
Methods
Fifty-two male Wistar rats (Charles River Breeding Laboratories) weighing 275-320 g were used
in these experiments. They were housed in a
temperature and humidity controlled environment with automatic lighting in 12 h cycles and
maintained on Purina rat chow and tap water ad
libitum.
Twenty-three animals had undergone uninephrectomy under ether anaesthesia 1 week
before the experiment. On the day of the
experiment they were again anaesthetized with
ether and had the remaining kidney removed.
Subsequently, a PE-50catheter was inserted into
the right external iliac artery and a PE-10
catheter into the right femoral vein. Both catheters contained a heparinized glucose (5%)
solution. Upon awakening, the animals were
maintained in a semirestrained position on a light
mesh screen for 60-90 min until their blood
pressure gradually rose to a steady baseline.
Twenty-nine animals with intact kidneys were
also catheterized in the same manner under light
ether anaesthesia and were then maintained in the
semirestrained position. In all animals, arterial
pressure was continuously monitored with a
Statham transducer and recorded on a Hewlett
Packard recorder (model 7702B).
‘Chemical sympathectomy’ was induced by
intraperitoneal injection of reserpine (Serpasil,
3 14s
P. Hatzinikolaou et al.
CIBA) at a dose of 0.1 mg/100 g body weight. subjected to chemical sympathectomy. Three
Four hours later, a first dose of cr-methyl hours after the second metyrosine dose they
p-tyrosine (metyrosine; Merck, Sharp and received an injection of the AVP antagonist. One
Dohme), 2.5 mg/100 g, was given intra- hour later two blood samples of 0.4 and 1 ml
peritoneally. The animals were maintained over- were drawn for determination of plasma catenight with an intravenous infusion of 5% glucose cholamines and plasma renin activity (PRA)
solution administered by a Harvard pump at a respectively.
rate of 0.006 ml/min for a total of approxiGroup 5 (n = 7) were rats with intact kidneys
mately 5 ml. Thirteen hours later a second dose subjected to chemical sympathectomy. Three
of metyrosine (2.5 mg/100 g) was injected hours after the second dose of metyrosine the
intraperitoneally. Suspension of metyrosine for teprotide infusion was started. One half hour
injection was prepared from 25 mg of metyro- later, when blood pressure had reached approxisine in 1.2 ml of sodium phosphate (0.5 mol/l)
mately pre-teprotide levels, the AVP antagonist
buffer, p H 7.4, and 0.8 ml of 5% methyl- was injected intravenously. Another 1 h later, a
cellulose (Fisher Scientific Co.).
0.4 ml blood sample was drawn for catecholThe peptide [ l-(B-mercapto-PB-cyclopenta- amine determination.
methylene propionic acid) 2-(O-methyl)tyroGroup 6 (n = 9) were rats with intact kidneys
sinelarginine vasopressin, which is an analogue subjected to chemical sympathectomy. Three
and competitive antagonist of arginine vaso- hours after the second metyrosine injection they
pressin (AVP) at the vascular receptor level [ l , had three samples of 0.4, 1 and 2 ml of blood
21, was used as an inhibitor of the vasocondrawn for determination of plasma catestrictor effects of AVP. A 2 mg amount of this cholamines, PRA and AVP.
compound was dissolved in a solution made from
Group 7 (n = 6) were intact rats catheterized
10 ml of 0.9% NaCl solution, 10 mg of bovine
and maintained overnight in the semirestrained
serum albumin and 3 pl of acetic acid, brought to
position with an intravenous glucose infusion.
pH 6.4 with NaOH. A dose of 0.15 ml of this
Twenty hours later they had three blood samples
solution containing 30 pg of the AVP antagonist
of 0.4, 1 and 2 ml drawn for determination of
was administered intravenously.
plasma catecholamines, PRA and AVP respecThe angiotensin converting enzyme inhibitor
tively, to be used as controls for comparison with
teprotide (SQ 20881, Squibb) was used as the manipulated groups.
inhibitor of the renin-angiotensin system. A
Plasma AVP [3, 41 and PRA [5] were
dose of 0 - 2 mg/100 g was dissolved in 0.9%
determined by radioimmunoassay. Plasma
NaCl solution and infused intravenously by a
catecholamines were measured by radioenzyHarvard pump over a 90 min period at a rate of
matic assay 161. Results are reported as means f
0.018 ml/min for a total of 1.6 ml.
SEM. Statistical evaluation was made with StuThe animals were divided into seven groups:
dent's f-test for paired or non-paired comparisons
group 1 (n = 8) rats were nephrectomized
as appropriate. Correlations were calculated by
animals subjected to chemical sympathectomy.
the Spearman rank correlation method. Results
Three hours after the second dose of metyrosine
were considered to be significant if P < 0.05.
they received an injection of the AVP antagonist
and 1 h later they had 0.4 ml of blood drawn for
Results
measurement of plasma catecholamine levels.
Group 2 (n = 7 ) were nephrectomized and
Blood pressures and hormone levels for each
chemically sympathectomized animals. Three
group of animals after each procedure are shown
hours after the second metyrosine injection they
in Table 1. Reserpine alone produced a small but
had two samples of blood, 2 ml and 0.4 ml,
significant fall in pressure in all animals and
drawn for determination of plasma AVP and
metyrosine caused a further drop in pressure. At
plasma catecholamine levels respectively.
20 h after the beginning of the experiment,
Group 3 (n = 7) were nephrectomized animals
injection of the AVP antagonist produced an
with sympathetic system intact. They were
abrupt lasting fall in blood pressure of nephrectocatheterized and maintained overnight with a 5%
mized animals. Rats with intact kidneys showed a
glucose infusion, and at approximately 20 h after
transient drop followed by a rapid gradual
the nephrectomy they had blood samples drawn
increase in pressure toward levels similar to those
as above for determination of plasma catepreceding the injection of AVP antagonist. In rats
cholamines and AVP to be used as controls in the
with intact kidneys who at 3 h after the second
anephric state.
metyrosine injection received infusion of the
Group 4 (n = 7) were rats with intact kidneys,
converting enzyme inhibitor teprotide, blood
Catecholamines, vasopressin, renin and blood pressure
315s
TABLE1. Changes in blood pressure, plasma renin activity and plasma hormones and deoxyphenylalanine induced by
depletion of catecholamines. converting enzyme inhibition and arginine vasopressin antagonism
A, Adrenaline; AVP, arginine vasopressin; NA, noradrenaline; PRA, plasma renin activity. In the fifth and sixth columns
pressures in parentheses are the subsequent elevations of blood pressures within a few minutes of the immediate blood pressure
falls shown.
~
Blood pressure (mmHg)
Group
Baseline
Reserpine Metyrosine Teprotide
PRA
(ng h-’ ml-’)
AVP
antagonist
~~
I ( n = 8)
anephric
2 ( n = 7)
anephric
3 ( n = 7)
anephric
4 (n = 7)
kidneys in situ
5 (n = 7)
kidneys in situ
6 ( n = 9)
kidneys in situ
7 ( n = 6)
kidneys in siru
109 f 1.5 9 8 f 1.7
85 f 5 . 2
107 f 2.5
80 f 4 . 3
93 f 4 . 3
AVP
NA
A
DOPA
129f22
73?20
<50
151 f 3 9
94f35
40
~~
~~
44 f 2.2
467f90
115 f 1.8
I I O f 2.4
Plasma hormones (pg/ml)
10.7 f 1. I 528 +_ 83 600 f I10 76 f 19
97 f 2.1
71 f 1.6
I10 f 1.4 92 f 1.6
74 f 4 . 0
I14 f 2.3
74 f 3.6
98 f 3 . 2
63 f 4.0
(73 f 4.0)
56 k 3.0
(66 ? 2.5)
52 +_ 3.3
111 f 3.1
pressure decreased abruptly, but transiently,
despite continuing teprotide infusion. When blood
pressure in these animals again reached the
pre-teprotide levels, injection of AVP antagonist
caused the blood pressure to fall further and stay
at that level for several hours. Groups 3 and 7 are
non-manipulated animals used to provide baseline hormone values for anephric and intact
animals respectively. Levels of AVP and adrenaline were significantly higher (P < 0.001 and P
< 0.05 respectively) in anephric animals. After
reserpine and metyrosine injections, catecholamines were markedly depleted in all groups so
treated: both noradrenaline and adrenaline were
significantly lower (P < 0.01 and P < 0.001
respectively) than control values in the anephric
animals, and in the animals with intact kidneys
(P < 0401 for both) compared with the control
values of each group.
Plasma levels of AVP were greatly stimulated
after catecholamine depletion in both the
anephric rats and the ones with intact kidneys (P
< 0.001 from their respective controls). Furthermore, the anephric rats with chemical sympathectomy (i.e. group 2) had significantly higher
AVP levels (P < 0.01) than their counterparts
with intact kidneys (i.e. group 6).
There was a highly significant correlation
between blood pressure levels and those of
noradrenaline (r = 0.925, P < 0.001) and
adrenaline (r = 0.8 10, P < 0.001) in groups 2, 3,
6 and 7, which received no AVP antagonist or
teprotide.
35 f 6 . 7
17.9f2.1
2.5 f 0 . 4
100?52
96 f 9
75 f 7
<50
8 7 f 16
7 6 f 14
<50
111+_18 9 4 f 1 4
<50
2 . 2 f 0 . 5 438 f 32 375
56
67 f 9
There was also a significant inverse correlation between levels of AVP and those of
noradrenaline (r = -0.724, P < 0 4 0 1 ) and
adrenaline ( r = -0.748, P < 0 4 0 1 ) in the same
four groups.
Plasma renin activity was measured in all rats
with intact kidneys except for those of group 5,
which received teprotide. It was significantly
higher than normal in those which had chemical
sympathectomy only and even more in those who
received in addition the AVP antagonist (P <
0.001 for both), and was inversely correlated
with blood pressure levels obtained after removal
of the sympathetic system and vasopressin
sequentially (r = -0.667, P < 0.02).
Discussion
Two rat. models were chosen, one anephric,
because in previous experiments we have found
that the plasma levels and pressor effects of
catecholamines and AVP seem to be very pronounced in nephrectomized animals [71, and one
with intact kidneys for comparison. Indeed, our
present data indicate that levels of AVP were
significantly higher in the anephric rats than in
those with kidneys in situ (i.e. groups 2 and 3 vs
groups 6 and 7 in Table l), which is compatible
with the kidney’s participation in the clearance of
AVP [Sl.
‘Chemical sympathectomy’ was accompanied
by gradual fall of blood pressure, indicating the
degree of contribution of the sympathetic system
316s
P. Hatzinikolaou et al.
to maintenance of blood pressures. Depletion of
catecholamines was associated with a marked
stimulation of AVP levels in an effort to maintain
blood pressure. There was a significant inverse
correlation between AVP levels and those of
noradrenaline and adrenaline, indicating that the
more pronounced the depletion of catecholamines, the more the AVP release was stimulated. This could partly be attributed to hypotension acting per se as a stimulus for secretion of
AVP [ 91 and partly to removal of the attenuating
or inhibitory influence of catecholamines on the
secretion of AVP [7, 10-121. In the anephric
model, the participation of AVP in maintaining
blood pressure after chemical sympathectomy
was far more important, as shown by both the
excessively high plasma AVP levels and the
magnitude and long duration of blood pressure
fall (average 40 mmHg) after injection of the
AVP antagonist (group 1).
On the other hand, rats with intact kidneys
seemed to have at least two more back-up
mechanisms to maintain blood pressure after
catecholamine depletion. Both plasma renin
activity and AVP release were significantly
stimulated by this manoeuvre (group 6). The
AVP antagonist produced a blood pressure fall of
only 15 mmHg on average, which within minutes
started increasing again toward pre-injection
levels. The high plasma renin activity levels at
that point suggest that stimulation of the reninangiotensin system tended to offset the hypotensive action of the AVP analogue in these
animals (group 4). When the catecholaminedepleted model with intact kidneys was subjected
to infusion of teprotide, which eliminated the
formation of angiotensin I1 [13], blood pressure
again fell temporarily, but soon returned to
pre-infusion levels despite continuing infusion of
teprotide (group 5). At that point, additional
administration of AVP antagonist had a marked
and lasting depressor effect, indicating that the
blood pressure-maintaining reserves were now
neutralized.
Arginine-vasopressin does not seem to play an
important role in blood pressure maintenance
under normal conditions, unless the subject has
suffered dehydration or haemorrhage [ 141, which
has compromised effective arterial pressure and
volume and increased plasma osmolality. The
renin-angiotensin system also does not contribute to blood pressure maintenance unless blood
pressure-lowering manoeuvres such as sodium
deprivation, diuretics, tilting etc. are applied
[15-171, in which case a compensatory renin
release tends to restore pressure to normal.
Recently, Andrews et al. [141, using the
anaesthetized dehydrated rat model, showed that
both angiotensin I1 and vasopressin assume an
important role in the homoeostasis of blood
pressure which has been compromised, but not in
the normal state. Our present experiments also
indicate that these two mechanisms become
important when another vasopressor mechanism,
the sympathetic system, has been interfered with.
Particularly in the renoprival state, stimulated
vasopressin accumulates to excessive levels and
assumes a major role in the maintenance of blood
pressure.
Acknowledgment
This work was supported in part by U.S.P.H.S.
Grant HL-183 18.
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