Clinical Science and Molecular Medicine (1978)55,363s-366s
The role of intrarenal vasoactive substances in the
pathogenesis of essential hypertension
K . A B E , M . Y A S U J I M A , N . I R O K A W A , M . S E I N O , S. C H I B A , Y. S A K U R A I ,
M . S A T O , Y. I M A I , K . S A I T O , T. I T O , T. H A R U Y A M A , Y. O T S U K A A N D
K. YOSHINAGA
Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan
Summary
To investigate the role of renal vasoactive
substances in the pathogenesis of essential hypertension, urinary prostaglandin E excretion, urinary
kallikrein excretion, plasma renin activity, plasma
aldosterone concentration and urinary Na excretion were measured in normal subjects and
patients with essential hypertension after
stimulation of the renin-angiotensin-aldosterone
system by the intravenous injection of frusemide or
a low Na diet; after the inhibition of reninangiotensin-aldosterone by an angiotensin I1 antagonist and after the inhibition of renal prostaglandin E synthesis by indomethacin. The urinary
excretions of prostaglandin E and kallikrein,
plasma renin activity and plasma aldosterone concentration increased after frusemide administration.
The urinary excretion of kallikrein increased after
frusemide or a low N a diet but decreased after the
angiotensin I1 antagonist and indomethacin during
Na depletion. Changes in urinary kallikrein excretion paralleled those in the renin-angiotensinaldosterone system after various stimuli. The
urinary excretion of prostaglandin E increased after
frusemide. However, a dissociation between the
urinary excretions of prostaglandin E and kallikrein was found during the low N a diet: the former
decreased and the latter increased. The urinary
excretion of prostaglandin E was closely related to
urinary Na output after various stimuli. Basal levels
of urinary prostaglandin E and kallikrein excretion
were lower in essential hypertension than in normal
Correspondence: Dr K. Abe, Department of Internal
Medicine, Tohoku University School of Medicine, Sendai
980, Japan.
subjects. The release of renal prostaglandin E and
kallikrein after frusemide was also suppressed in
essential hypertension compared with that in
normal subjects. The data indicate that renal
kallikrein-kinin
and
renin-angiotensin-aldosterone may interact in a dynamic fashion to
maintain blood pressure, that renal prostaglandin E
may be involved in renal N a handling and that the
suppression of renal kallikrein-kinin and prostaglandin E in essential hypertension may be an
etiological factor in essential hypertension.
Key words: essential hypertension, pathogenesis,
renal prostaglandin E, renal kallikrein-kinin, reninangiotensin-aldosterone system.
Abbreviations: KK, kallikrein-kinin; PG, prostaglandin; RA, renin-angiotensin; RAA, reninangiotensin-aldosterone.
Introduction
It is now generally accepted that the kidney is
involved in the pathogenesis of hypertension
through two mechanisms. One is the renin-angiotensin system and the other the renal antihypertensive mechanism. Margolius, Horwitz,
Pisano & Keiser (1974) reported that synthesis of
renal kallikrein is regulated by aldosterone. McGiff,
Itskovitz, Terragno & Wong (1976) reported that
there is a close interrelationship between the renal
KK system and renal PG. Thus, renal KK and P G
may possibly regulate blood pressure by opposing
the action of the RAA system. The present study
was undertaken to investigate the role of renal
vasoactive substances in the pathogenesis of
363s
364s
K . Abe et al.
essential hypertension. In addition, we examined
the interrelationship between RAA, renal kallikrein, renal P G and sodium status.
Methods
The present study was carried out in 84 normal
subjects and 55 patients with essential hypertension. Normal subjects were 61 men and 23
women (mean age 40.0 t 1.6, range 18-66 years).
Essential hypertensives were 35 men and 20
women (mean age 37.1 k 1.8, range 15-63 years).
All subjects were hospitalized during the study and
allowed an unrestricted sodium diet. Antihypertensive medication was discontinued for at least 2
weeks before the study. Urine was collected in a
bottle kept in a refrigerator and then stored at
-15OC until the assay. Blood was sampled in
fasting patients kept in the recumbent position for
one hour. In some patients, sampling of blood and
urine was performed after the following
manipulations; low Na diet, frusemide injection and
upright posture, infusion of angiotensin I1 antagonist, and administration of indomethacin.
Urinary PGE was measured radioimmunologically by using a commercial kit. After urinary
PGE had been converted into PGB by alkaline
treatment, the sample was acidified to pH 3-4 and
extracted with ethyl acetate. The PGB fraction was
then separated by silicic acid column chromatography and measured radioimmunologically with
PGB antiserum. Urinary PGE was calculated by
subtraction of the value of natural PGB. The
overall recovery rate of added PGE was 54.8
0.7%, and the estimated value was corrected by
this factor.
Urinary kallikrein was measured as kininogenase activity. Urine, 0.05-0.1 ml, was incubated
with 4 pg of bovine serum low-molecular-weight
kininogen at 37OC for 20 min. After incubation, the
sample was heated at 8OoC for 20 min to terminate
the enzymic reaction and the generated kinin was
measured by radioimmunoassay using kallidin antiserum. In the present method, an extraction
procedure for kinin was not necessary, because
bovine serum low molecular weight kininogen had
no cross reaction with kallidin antibody.
Plasma renin activity was determined by a
modification of Haber's method (Abe et al., 1972)
and plasma aldosterone concentration with a commercial radioimmunoassay kit (Cer. Ire. Sorin.).
Urinary Na was measured by autoanalyzer. The
results were expressed as means k SEM. The differences between mean values were tested by Student's t-test.
Results
Urinary excretion of PGE and kallikrein in normal
subjects and essential hypertensive patients
Resting levels of the urinary excretions of PGE
and kallikrein were 736 & 32 ng/day and 34.5 jr
4.0 ,ug 20 min-I day-', respectively, in 84 normal
subjects, and 394 k 29 ng/day and 18.3 t 2.8 pg
20 min-' day-', respectively, in 55 patients with
essential hypertension. The urinary excretions of
PGE and kallikrein were significantly lower in
patients with essential hypertension than in control
subjects (PGE P < 0.001, kallikrein P < 0.001).
There was a significant correlation between the
urinary excretions of PGE and N a in 84 normal
subjects (r = 0.39, P < 0.001) and in 51 patients
with essential hypertension ( r = 0.62, P < 0.001).
However, the urinary excretion of kallikrein was
not significantly correlated with that of Na or PGE.
Influence of low Na diet on renal vasoactive substances
Ten patients received first a diet containing 200
mmol of Na/day for at least a week, then 100
mmol and finally 30 mmol of Na, each for 3 days.
PRA, PAC and urinary kallikrein excretion
increased with the low Na diet. On the contrary,
urinary Na and PGE excretions decreased. Thus,
the low Na diet induced a dissociation between
renal PGE and the kallikrein system.
Effect of frusemide on renal vasoactive substances
After the RAA system had been stimulated by
frusemide injection and an upright posture for 2 h
in 19 normal subjects and 16 patients with essential
hypertension, urinary PGE and kallikrein excretions were measured. Values of all the variables
measured increased after frusemide administration
(Fig. 1). The increment of plasma renin activity and
plasma aldosterone concentration was similar in
normal subjects and in essential hypertension. On
the contrary, the increments of urinary PGE and
kallikrein excretions after frusemide administration
were greater in normal subjects than in those with
essential hypertension. The present results suggest
that the responses of both renal PGE and renal
kallikrein to frusemide are suppressed in essential
hypertension.
Effect of angiotensin II antagonist on renal vasoactive substances
After the angiotensin I1 antagonist, 1 -sarcosine8-isoleucine angiotensin 11, was infused intra-
Vasoactive substances in essential hypertension
365s
Control
100
f
'P<005
P < 0 01
f
*** P < 0 005
80
80
60
h
e
60
M
40
40
40
L
II
20
20
-
0
0
10
I
1.1
T
0
1
T
20
-
0
..
T
'f'
5
5
cI
.
0
0,
M
8
10
V
2
0
0
80
h
600
f
20
I-
1
10
0
**.
60
60
40
40
20
20
z
400
400
200
200
E
v
Healthy
( n = 191
-0
0
0
0
E H
I n = 161
Healthy
( n = 191
E H
( n = 16)
FIG. 1. Effect of frusemide injection on urinary kallikrein (U,,,V) excretion, urinary PGE excretion
(U,,, V), plasma renin activity (PRA), plasma aldosterone concentration (PAC), urinary volume (UV)
and urinary sodium excretion (U,,V) in healthy subjects (n = 19) and patients with essential hypertension (n = 16). Results are presented as mean values f SEM.
venously at a rate of 300-600 ng/kg/min in 10
patients with essential hypertension, the urinary
excretions of PGE and kallikrein were measured.
During a normal Na diet, blood pressure rose as a
result of the agonistic action of this analogue. The
urinary excretions of PGE and Na, and plasma
renin activity decreased after the administration of
this drug, whereas those of kallikrein and plasma
aldosterone concentration increased. During the
low Na diet, blood pressure was lowered by the
antagonistic action of the analogue. The urinary
excretion of kallikrein and plasma renin activity
decreased, while the urinary excretions of PGE and
Na, and plasma aldosterone concentration did not
change. The results suggest that circulating angiotensin I1 might be one of the regulators of urinary
kallikrein excretion.
Effect of indomethacin on renal vasoactive
substances
Eleven hypertensive patients were given a 90
mmol Na diet with frusemide (80 mg per day
366s
K . Abe et al.
orally) for 3 days, after which indomethacin (150
mg per day orally) was added for an additional 3
days. The urinary excretion of PGE, plasma renin
activity and plasma aldosterone concentration decreased significantly after indomethacin (PGE P <
0.05, plasma renin activity, P < 0.01, plasma aldosterone concentration P < 0.01). The urinary
excretions of kallikrein and Na decreased slightly,
but the changes were not significant.
Discussion
Kaizu & Margolius (1975) reported that kallikrein
release in the rat renal cortical cell suspension
could be increased by aldosterone and reduced by
spironolactone. On the other hand, Johnston,
Mattews & Dax (1976) suggested that angiotensin
I1 might be a regulator of urinary kallikrein
excretion. In the present study, changes in the
urinary excretion of kallikrein paralleled those of
the RAA system after various stimuli. Kallikrein
output increased after the administration of frusemide or a low Na diet, but it decreased after the
administration of the angiotensin I1 antagonist and
indomethacin during Na depletion. These results
indicate that the renal kallikrein-kinin system may
interact with the RAA system in a dynamic fashion
to maintain blood pressure.
Urinary kallikrein and PGE excretion rose after
frusemide, and fell after indomethacin. However, a
dissociation between renal kallikrein and PGE was
found after Na depletion and after the administration of the angiotensin I1 antagonist during
a normal Na diet.
Previous reports concerning the role of renal
PGE in renal Na handling have been conflicting.
Intrarenal infusion of PGE induces natriuresis
(Johnston, Herzog & Lauler, 1967, indicating that
renal PGE may be involved in renal Na output. On
the contrary, the study by Tobian, O’Donnell &
Smith (1974), in which renal PGE content in the
rat decreased after Na repletion, suggests that renal
PGE may act as an antinatriuretic hormone. In the
present study, the urinary excretion of P G E was
closely related to urinary N a , output after various
stimuli. A significant correlation was also found
between basal levels of urinary PGE and those of
urinary Na. The results indicate that renal PGE
may be involved in renal Na handling.
Elliot & Nuzum (1934) found that the urinary
excretion of kallikrein decreased in essential hypertension. A similar result was reported by Margolius, Geller, Pisano & Sjoerdsma (1971). In the
present study, basal levels of urinary PGE and
urinary kallikrein were lower in essential hypertensive than in normal subjects, as also were the
responses of renal PGE and kallikrein to frusemide
injection. These results suggest that suppression of
the renal kallikrein-kinin system and renal PGE
may be an etiological factor in essential hypertension.
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