European Journal o f Pharmacology, 33 (1975) 151--157 © North-Holland Publishing Company, Amsterdam -- Printed in The Netherlands

E F F E C T OF DOPAMINE ON RENIN SECRETION IN THE ANESTHETIZED DOG JEAN-LOUIS IMBS, MARIETTE SCHMIDT and JEAN SCHWARTZ Institut de Pharmacologic et de Mddecine Expdrimentale (E.R.A. au CNRS No. 142) Facultd de Mddecine, 11 rue Humann, 67000 Strasbourg, France Received 10 December 1974, revised MS received 27 February 1975, accepted 28 April 1975

J.L. IMBS, M. SCHMIDT and J. SCHWARTZ, Effect o f dopamine on renin secretion in the anesthetized dog, European J. Pharmacol. 33 (1975) 151--157. Intrarenal perfusion of dopamine (6 pg/kg/min for 10 min) causes a significant increase of renin secretion, together with a significant increase in renal blood flow. This renin hypersecretion is not accompanied by any significant alteration in renal perfusion pressure, kalemia or natriuresis. The role of intrarenal dopaminergic receptors has been studied: (a) Haloperidol (intrarenal perfusion of 50 pg/kg/min for 20 rain) suppresses the renal vasodilation and renin hypersecretion induced by dopamine. (b) Propranolol (intrarenal perfusion of 1 mg/kg in 15 rain, then of 4 mg/kg/hr)alters neither the renal vasodilation nor the renin hypersecretion induced by dopamine. These observations support the assumption that the dopaminergic receptors are brought into play in the two renal responses to dopamine studied by us.

Renal blood flow

Dopamine

Haloperidol

1. Introduction There are many convergent proofs that the autonomic nervous system participates in the control of renin secretion. A sympathetic mediation of renin release involving fl-adrenergic receptors has been recognized (Meurer, 1971; Passo et al., 1971; Assaykeen et al., 1974). The possible role of dopamine in the sympathetic control of renin secretion has not been extensively considered. Some of the data suggest, however, that dopamine acts specifically on the kidney. This organ contains large quantities of dopamine (Anton and Sayre, 1964) and responds in a special way to exogenous dopamine. Goldberg (1972) and Toda and Goldberg {1973) suggested the existence of renal dopaminergic receptors, stimulation of which

Propranolol

Renin secretion

induces vasodilation which is antagonized by dopaminolytic neuroleptics (McNay et al., 1965; Yeh et al., 1969; Brotzu, 1970). The intrarenal mode of action of dopamine appears at first sight complex: a priori its effect on renin secretion may be due to stimulation of dopaminergic receptors, and/or to direct stimulation of fl-adrenergic receptors preceded or not by metabolic transformation of dopamine, and/or to an alteration of the uptake mechanisms at the level of the adrenergic nerve endings. Here we have studied the effects of dopamine on the blood flow and renin secretion of a denervated kidney. This renal response to dopamine was studied after administration of a dopaminolytic agent, haloperidol, or of a flblocking agent, propranolol.

152

2. Materials and methods

2.1. General procedure 17 mongrel dogs (mean weight: 20 kg) were operated after an 18 hr fast during which they had free access to water. After premedication with levomepromazine (0.5 mg/kg s.c.) they were rapidly anesthetized with pentobarbital (15 mg/kg i.v., then 1 to 2 mg/kg i.v. as required). The left kidney, reached by lumb o t o m y , was isolated from the adjacent organs. Its vasculo-nervous pedicle was dissected; the nerves, lymphatics, collateral blood vessels and periarterial sheath were coagulated, then sectioned. The ureter was catheterized and sectioned. The kidney was thus denervated. Its lymphatic drainage was suppressed, its sole effluent being the renal vein. Polyethylene catheters used for taking blood samples were placed in the left renal vein through the previously ligated ovarian or spermatic vein and in the suprarenal aorta, through a lumbar artery. These two catheters were equipped with a flexible tygon tube passing under the vanes of a rotary pump, thus permitting simultaneous aspiration at constant rate of arterial and venous blood. The animal was allowed to rest for two hours before measurements were begun. Once these were completed, the kidney was removed and weighed.

2. 2. Drugs and modes of administration 3-hydroxytyramine hydrochloride (Sigma), d,l-propranolol hydrochloride (ICI), haloperidol (Haldol: 5% ampuls, Lab. Le Brun) were perfused into the left renal artery at constant rate (0.1 ml/min Chronofuseur Braun) through a needle (external diameter 0.35 mm) inserted into the artery. Propranolol and dopamine were dissolved in a 5% glucose solution.

2. 3. Experimental pro toco Is In all experimental situations dopamine was perfused at doses of 6 pg/kg/min over a period of 10 min.

J.L. IMBS ET AL.

2.3.1. For 11 animals, the protocol included 2 periods of 10 min each. The first period allowed the basal values to be measured, modification of these values by dopamine being studied in the subsequent period. 2.3.2. Renal response to dopamine was observed during an intrarenal perfusion of 50 pg/kg/min of haloperidol over a period of 20 min. This protocol was followed in 3 dogs. 2.3.3. After evaluation of the renal response to dopamine, an intrarenal perfusion of propranolol (67 pg/kg/min) was given. The suppression of renal vasodilation following injection of 0.25 pg/kg of isoproterenol into the renal artery makes it possible to verify the blocking of ~-adrenergic receptors of the renal vascular bed. This result was obtained with a mean dose of 1 mg/kg of propranolol perfused over a period of 15 min. The response to dopamine was then again measured, while propranolol perfusion (4 mg/kg/hr) was continued. This protocol was followed in 3 dogs. 2.3.4. 3 control dogs were studied. For 2 of these a protocol of 6 periods of 10 min was followed and the spontaneous changes of the different parameters evaluated in the absence of perfusion of an active substance. In the third, the renal response to dopamine was evaluated during intrarenal perfusion of the solvent used for the administration of haloperidol (perfusion over a period of 20 min at a rate of 0.1 ml/min of a solution of 0.5 ml lactic acid, 50 mg methyl paraoxybenzoate and 5 mg propyl paraoxybenzoate in 100 ml distilled water). 2. 4. Measurements and dosages These were begun 4 hr after induction of anesthesia, at which time the animal was heparinized (Heparine Choay 1000 u/kg i.v.). The renal blood flow was measured by electromag-

DOPAMINE AND RENIN SECRETION

netic flowmeter (Nycotron). We used an integrator which measures the cumulative blood flow over a given period of time. Our results show the mean value of this flow expressed in ml/min/g of kidney, calculated from the flow integrated during the final 8 rain of an experimental period. Diuresis, natriuresis and kalemia (flame photometry) and the arterial hematocrit were measured for each period. Plasma renin activity (PRA, ng Angiotensin I liberated in 1 ml of plasma during 1 hr incubation) was determined by radio-immunoassay (Haber et al., 1969). It was measured in 8 ml of renal venous and arterial blood, taken simultaneously at a rate of 1 ml/min during the final 8 min of an experimental period. The blood was pumped directly into chilled plastic tubes containing 0.4 ml of 3.8% EDTA pH 6.5. Renin secretion rate was calculated as (renal venous PRA -- systemic arterial PRA) × renal plasma flow (ml/min/g of kidney), and expressed as ng angiotensin I per min and per g of kidney. The renal plasma flow was calculated from the hematocrit.

R BF

(mllminlg)

~. H A L O P E R I D O L ~----0

153

2.5. Statistical evaluation Friedman two-way analysis of variance by ranks (in Siegel, 1956) and Student's t-test on matched pairs are used. p/> 0.05 are considered non-significant.

3. Results 3.1. Dopamine and renin secretion (table 1) Dopamine perfusion leads to a significant increase in renal venous PRA, arterial PRA and renin secretion. This renin hypersecretion was observed in each of the animals studied. It was accompanied by a constant increase in renal blood flow. There was no variation in arterial pressure or in kalemia and a slight but not significant increase in diuresis and natriuresis. 3. 2. D o p a m ine, haloperidol and ren in secretion Like other investigators (Yeh et al., 1969) we noted that haloperidol suppressed the renal vasodilation induced by dopamine (fig. 1). Similarly haloperidol suppressed the dopamine perfusion-linked renin hypersecretion (table 2) in each of the 3 dogs studied.

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PROPRANOLOL /

/

/

J

/

3.3. Dopamine, propranolol and renin secretion

s"

/ /// of

i'

/f j/ /f / 10 // t/t

///1

Renal response to dopamine persisted during administration of propranolol. The renal vasodilating response persisted (fig. 1) and this finding is in agreement with published data (McNay et al. 1965). Renin hypersecretion induced by dopamine also persisted (table 3). 3. 4. Control dogs

DOPAMINE 1 , 6 p g J m J n l k g 10 r a i n }

Fig. 1. The renal b l o o d flow ( R B F ) response to dopamine was suppressed during an intrarenal infusion of haloperidol (50 pg/kg/min/20 rain). The renal vasodilating response to d o p a m i n e was not modified by an intrarenal infusion o f p r o p r a n o l o l (1 m g / k g in 15 min t h e n 4 mg/kg/hr).

Renin secretion did not vary spontaneously between periods 1 and 2, 3 and 4, or 5 and 6 in the 2 dogs for which a protocol of 6 periods of 10 min was followed (table 4). In the third control dog perfusion of the lactic acid--parao x y b e n z o a t e solvent prevented neither renin

154

J.L. IMBS ET AL

TABLE 1 Dopamine action on renin secretion. Mean values (S.D.) recorded before and during intrarenal dopamine perfusion. Statistical analysis by two-tailed t-test on matched pairs (NS, p ~ 0.05). n = 11

Control

Dopamine

p

( 6pg/kg/min/l O rain) ArterialPRA (ng angio. I/ml plasma/hr)

2.4

(1.34)

4.62 (2.07)

~0.001

Renal venous PRA (ng/ml/hr)

3.04 (1.81)

6.23 (3.18)

~ 0.001

Renin secretion (ng anglo. I/rain/g)

1.44 (2.14)

~4.76 (5.63)

~ 0.05

Renal blood flow (ml/min)

3.80 (1.49)

4.58 (1.87)

~ 0.00l

Blood pressure (ram Hg)

114

(14.4)

112

(16.2)

NS

Diuresis (pl/min)

178

(95.8)

212

(89.5)

NS

29

(19.2)

35

(16.3)

NS

(0.58)

NS

Natriuresis (pEq/min) Blood potassium (mEq/l)

3.9

(0.43)

3.8

TABLE 2 Suppression of the renin response to dopamine (6 pg/kg/min/lO rain) by an intrarenal perfusion of haloperidol (50 pg/kg/min/20 min). Mean values (S.D.) recorded before and during intrarenal perfusion of dopamine + haloperidol. Variations statistically non significant (t-test on matched pairs). n=3

Control

Dopamine + haloperidol

Arterial PRA (ng/ml/hr)

1.79 (0.49)

2.52 (0.80)

Venous PRA (ng/ml/hr)

2.21 (0.77)

3.10 (1.38)

Renin secretion (ng anglo. I/rain/g)

0.53 (0.20)

0.66 (0.55)

Blood pressure (mm Hg)

137

(11)

133

(21)

Diuresis (pl/min)

456

(210)

466

(295)

Natriuresis (/~Eq/min) Blood potassium (mEq/1)

68 3.9

(30) (0.3)

70 3.7

(37) (0.3)

DOPAMINE AND RENIN SECRETION

155

TABLE 3 Action of propranolol (intrarenal perfusion of 1 mg/kg in 15 min then 4 mg/kg/hr). The first 3 lines schematize the sequence of experimental period. Mean values (S.D.). Statistical analysis by the Friedman analysis of variance (X r2 ) and by the one-tailed t-test on matched pairs, comparing the period 1 to 2 and to 4 (*p < 0.05).

4

2

Period Dopamine (6 pg/kg/min )

I

7/-JJ

Propranolol

n=3

Xr 2

Arterial PRA (ng/ml/hr)

1.53 (1.05)

2.19 (1.48)

1.89 (1.44)

2.28 (0.29)

< 0.02

Venous PRA (ng/ml/hr)

1.71

3.68 (1.85)

2.59 (1.55)

4.65 (0.17)

< 0.02

(0.99)

Renin secretion (ng anglo. I/min/g)

0.41 (0.14)

5.53 (3.93)

2.17 (1.40)

7.07* (3.18)