Expanding the Distinctive Neuroimaging Phenotype of ACTA2 Mutations

BACKGROUND AND PURPOSE

Arg179His mutations in ACTA2 are associated with a distinctive neurovascular phenotype characterized by a straight course of intracranial arteries, absent basal Moyamoya collaterals, dilation of the proximal internal carotid arteries, and occlusive disease of the terminal internal carotid arteries. We now add to the distinctive neuroimaging features in these patients by describing their unique constellation of brain malformative findings that could flag the diagnosis in cases in which targeted cerebrovascular imaging has not been performed.

MATERIALS AND METHODS

Neuroimaging studies from 13 patients with heterozygous Arg179His mutations in ACTA2 and 1 patient with pathognomonic clinicoradiologic findings for ACTA2 mutation were retrospectively reviewed. The presence and localization of brain malformations and other abnormal brain MR imaging findings are reported.

RESULTS

Characteristics bending and hypoplasia of the anterior corpus callosum, apparent absence of the anterior gyrus cinguli, and radial frontal gyration were present in 100% of the patients; flattening of the pons on the midline and multiple indentations in the lateral surface of the pons were demonstrated in 93% of the patients; and apparent "squeezing" of the cerebral peduncles in 85% of the patients.

CONCLUSIONS

Because α-actin is not expressed in the brain parenchyma, only in vascular tissue, we speculate that rather than a true malformative process, these findings represent a deformation of the brain during development related to the mechanical interaction with rigid arteries during the embryogenesis.

Fat-free mass loss generated with weight loss in overweight and obese adults: What may we expect?

There is concern that intentional weight loss may generate excessive loss of fat-free mass (FFM). Idealists target minimal loss of FFM, while others consider that FFM loss of up to 25% of weight loss is acceptable. In a cross-sectional study of 275 weight-stable, overweight or obese adults, we used whole-body dual-energy X-ray absorptiometry to measure FFM. A range of models was used to estimate the expected ΔFFM/Δweight ratio required to attain the body composition of a weight-stable individual at a lower body mass index (BMI). Higher BMI was associated linearly with higher FFM in men and women. Proportional ΔFFM/Δweight was influenced by sex, BMI and age. Direct scatter plot analysis, quadratic curve fit modelling and linear FFM-BMI modelling provided similar estimates for each model of ΔFFM/Δweight ratio, with 40% for men and 33% for women. These results show that the 25% rule is inappropriate and our estimates are higher than those generally reported after intentional weight loss indicating favourable preservation of FFM.

Blockade of AT1 receptors by losartan did not affect renin gene expression in kidney medulla

This study was designed to determine particular changes in the renin gene expression and activity in renal cortex and medulla after AT(1) receptor blockade. It was found that two-week-treatment with AT(1) blocker losartan induced an increase in tissue renin activity in both parts of kidney causing subsequent elevation of plasma renin activity. Renin mRNA in losartan-treated rats was increased only in cortex, suggesting cortex origin of elevated renin activity in medulla. Medullary renin mRNA indicated local synthesis of renin within the whole kidney and supported the idea of the presence of tissue renin-angiotensin system. Our results show that gene expression of renin in kidney medulla is insensitive to AT(1) receptor blockade and this points out that the regulation of kidney renin-angiotensin system probably differs from that in cortex.

Mild acute renal failure potentiates metformin accumulation in the diabetic rat kidney without further impairment of renal function

OBJECTIVES

To analyze, in acute renal failure (ARF) in diabetic rats, how moderate functional ARF would modify metformin (MET) pharmacokinetics and if plasma and renal tissue MET accumulation could aggravate renal insufficiency and/or elicit plasma lactate accumulation.

METHODS

Streptozotocin-induced diabetic rats were allocated to four groups: control, MET, ARF, ARF-MET (6-7 rats per group). MET (100 mg/kg/day) was given per os for two weeks before ARF was induced by drinking restriction and enalapril treatment. The effects of MET and/or ARF were examined in vivo on renal function in conscious rats (metabolic cages) and ex vivo on renal vascular reactivity (isolated kidney).

RESULTS

MET treatment (plasma level: 5.3 +/- 1.4 microg/ml, mean+/-SEM), resulted in biguanide accumulation in cortex and medulla (53 +/- 17 and 80 +/- 40 microg/g respectively). MET was devoid of any effect on creatinine clearance, mean blood pressure or renal vascular resistance, but moderately increased plasma lactate (3.8 +/- 0.5 vs 3.2 +/- 0.2 mM, P<0.05) and decreased angiotensin II-induced renal vasoconstriction. ARF, although mild, decreased renal MET clearance (0.29 +/- 0.05 vs 1.01 +/- 0.31 ml/min/100 g, P<0.05) and increased plasma and renal tissue MET levels (x 2-4). MET however did not worsen the fall in glomerular filtration rate, nor modify renal vascular reactivity. ARF did not change the MET-elicited moderate increase in plasma lactate.

CONCLUSION

Despite the increase in MET plasma and renal tissue levels subsequent to moderate ARF, no harmful metabolic effect on plasma lactate and no further impairment of renal function was observed in MET-treated diabetic rats subjected to ARF.

Withdrawal reveals lack of effect of prolonged antihypertensive treatment on intrinsic aortic wall stiffness in senescent spontaneously hypertensive rats

1. Chronic antihypertensive treatment lowers cardiovascular morbidity and mortality. The beneficial effect on the blood vessel wall may be due to the lowering of blood pressure (BP) and, hence, wall stress (WS), or to a treatment-induced change in wall structure. 2. We have previously shown that, when evaluated at the same level of BP and WS, the stiffness of the aortic wall of old spontaneously hypertensive rats (SHR) is higher than that of young and adult SHR and that of age-matched Wistar-Kyoto (WKY) rats. In the present study, we tested the hypothesis that the intrinsic changes in wall composition and mechanics in old SHR can be modulated by long-term treatment with an angiotensin I-converting enzyme inhibitor (captopril; 40 mg/kg per day) combined with a diuretic (hydrochlorothiazide; 20 mg/kg per day) and that treatment withdrawal would reveal whether such changes are maintained when BP and WS return to pretreatment levels. 3. We evaluated aortic structure and mechanics in SHR following 1 week withdrawal of oral antihypertensive treatment from 3 to 15 months of age (n = 8). Results were compared with age-matched SHR that were maintained on treatment (n = 12) or were not treated (n = 13) and with WKY rats (no treatment n = 11; maintained n = 11; withdrawn n = 10). 4. Isobaric aortic wall stiffness was estimated from the ratio of baseline aortic pulse wave velocity (PWV) to BP and the slope relating aortic PWV to BP following sodium nitroprusside-induced hypotension. Relative wall stiffening was estimated as the ratio of elastic modulus (EM) to WS. We argued that if treatment produced a change in wall elastin or collagen content, with a subsequent decrease in isobaric wall stiffness, then this would be maintained when BP increased following withdrawal of treatment. 5. In old SHR, treatment lowered isobaric wall stiffness (baseline PWV/BP 4.6 +/- 0.3 cm/s per mmHg; slope relating PWV to BP 6.7 +/- 0.4 x 10-3 cm/s per mmHg and EM/WS 4.1 +/- 0.4 vs 6.1 +/- 0.4 cm/s per mmHg, 9.7 +/- 0.9 x 10-3 cm/s per mmHg and 8.9 +/- 1.1, respectively, without treatment; all P < 0.05). After 1 weeks treatment withdrawal, the indices (5.7 +/- 0.2 cm/s per mmHg, 9.1 +/- 0.2 x 10-3 cm/s per mmHg and 7.2 +/- 0.6) increased in parallel with the increase in WS to levels similar to those observed in untreated SHR. There were no significant differences among the WKY rat groups. 6. Treatment increased the elastin and collagen contents of the aortic wall in both SHR (196 +/- 13 and 128 +/- 5 vs 111 +/- 9 and 86 +/- 4 mg/g wet weight, respectively, in untreated; P < 0.05) and WKY rats (190 +/- 19 and 135 +/- 4 vs 115 +/- 7 and 114 +/- 5 mg/g wet weight, respectively, in untreated; P < 0.05). This increase remained following withdrawal (213 +/- 26 and 118 +/- 4 vs 161 +/- 14 and 127 +/- 4 mg/g wet weight in SHR and WKY rats, respectively). 7. In summary, 1 year of treatment with captopril plus hydrochlorothiazide increases wall elastin content and reduces WS and stiffness in old SHR. Following withdrawal, elastin content remains high, but wall stiffness parallels WS in a manner similar to that in untreated SHR.

Involvement of brain mineralocorticoid receptor in salt-enhanced hypertension in spontaneously hypertensive rats

We recently showed that brain mineralocorticoid receptors (MRs) are involved in blood pressure and kidney function control in normotensive Wistar rats. We now assessed the involvement of brain MRs in spontaneously hypertensive rats (SHR), in which the presence of adrenocorticoids has been shown to be required for the development of hypertension. The effect of a single intracerebroventricular (ICV) injection of an MR antagonist (RU28318) on systolic blood pressure (SBP) and renal function was examined in conscious adult SHR and Wistar-Kyoto rats (WKY) maintained on a standard-sodium diet (0.4% Na(+)). In WKY, a long-lasting decrease in SBP was caused by the ICV injection of 10 ng RU28318 as previously reported in Wistar rats, associated with increased urinary excretion of water and electrolytes. In SHR maintained on the standard diet, the ICV injection of RU28318 (10 or 100 ng) had no effect on cardiovascular and renal functions. However, the ICV injection of 10 ng RU28318 in SHR after 3 weeks of high sodium intake (8% Na(+)) caused a long-lasting decrease in SBP. The effect was present at 8 hours (DeltaSBP 34+/-2 mm Hg), persisted at 24 hours (DeltaSBP 29+/-1 mm Hg), and disappeared at 48 hours after the injection. The hypotension was not associated with changes in heart rate, urinary excretion of water and electrolytes, and plasma renin activity, whereas renal denervation did not affect the decrease in SBP. A more pronounced decrease in SBP (49+/-3 mm Hg at 8 hours) was observed with 100 ng RU28318. This dose of the antagonist was without effect after subcutaneous administration. Thus, brain MRs appear to participate in the maintenance of hypertension in conscious adult SHR sensitized by sodium loading.

[Effect of a non-antihypertensive dose of ramipril on the plasma and tissue renin-angiotensin system in 27 TGR (mRen2) rats]

It is admitted that low dose of angiotensin converting enzyme (ACE) inhibitors allows the regression of left ventricular hypertrophy (HVG) in experimental models where plasma renin activity (PRA) is high. The use of low dose of ramipril, an ACE inhibitor, make it possible to explore the place of cardiac renin-angiotensin system (RAS) in the regression of HVG independently of blood pressure (BP). Twenty rats TGR (mRen2) 27, heterozygous male, 10 weeks old were treated by daily oral gavage during 6 weeks by 10 micrograms/kg/jour ramipril or distilled water and compared to 10 normotensive Sprague Dawley (SD) rats. BP was measured. After the period of treatment, plasma, left kidney and the ventricles were removed. On each tissue samples and plasma, angiotensinogen (Aogen), the renin activity, angiotensins I (Ang I) and II (Ang II) were determined by radioimmuno assay and the activity of ACE was measured by fluorimetry. BP does not differ between treated and untreated groups during 6 weeks of treatment but is significantly higher compared to SD rats. PRA of untreated rats is high (36 +/- 5 ng Ang I/mL/h). However, treatment did not make it possible to decrease HVG. In plasma and kidney treatment's effect on SRA is confirmed by the increase in renin activity (plasma: 63 +/- 9 vs 36 +/- 5 ng Ang I/mL/h; kidney: 127 +/- 11 vs 92 +/- 7 micrograms Ang I/g/h) which is accompanied by an increase of Ang I rates (plasma: 297 +/- 31 vs 15 +/- 10 fmol/mL; kidney: 241 +/- 37 vs 160 +/- 12 fmol/g) and of the reduction in Aogen. An inhibition of ACE is perceptible with low dose of ramipril in heart (left ventricle: 1.7 +/- 0.1 vs 2.5 +/- 0.3 nmol HisLeu/min/mg protein), but it does not appear significant modifications of the other elements of the RAS in this tissue. The Ang II cardiac rates are probably not solely defined by cardiac ACE activity, other ways of synthesis being described. The absence of regression of the HVG in TGR (mRen2) 27 rat with low dose of ramipril could be related to the absence of effect on cardiac Ang II rates. In addition, the relation between high PRA rates and the effectiveness of low dose of ACE inhibitor in the HVG are not confirmed.

Effects of icatibant on the ramipril-induced decreased in renal lithium clearance in the rat

The interaction between an inhibitor of angiotensin I converting enzyme (ramipril) and renal lithium handling was analysed in conscious, normotensive Wistar rats in the absence or the presence of a specific bradykinin B2 receptor antagonist, icatibant. The rats were treated for 5 days with ramipril (1 mg/kg/day p.o.) or its vehicle, alone or together with icatibant (0.1 mg/kg/day, s.c. infusion). Lithium chloride (8.3 mg/kg i.p.) was given as a single dose on day 5. Systolic blood pressure and heart rate were measured by tail plethysmography on day 3 (3, 9 and 15 h after ramipril administration) and renal function on day 4 (0-6 and 6-24 h urine sampling) and day 5 (0-6 h urine sampling). In another group of rats, 24 h sodium excretion was assessed during the first 4 days of ramipril treatment. Ramipril decreased renal lithium clearance (90+/-8 vs. 142+/-10 microl/min/100 g, P<0.001, n=24) and increased the fractional lithium reabsorption (74.3+/-1.9 vs. 66.7+/-1.7%, P<0.05) and plasma lithium concentration (0.108+/-0.006 vs. 0.085+/-0.004 mM, P<0.01). Alteration of renal lithium handling by ramipril was associated with a decrease in systolic blood pressure (-15% 3 h after ramipril administration) and sodium excretion (0-6 h after ramipril). The 24-h sodium excretion, however, tended to increase. Icatibant had no effect per se on renal function but attenuated the ramipril-induced decrease in renal lithium clearance (118+/-16 vs. 90+/-8 microl/min/100 g, n=12 and 24 respectively, P<0.05 one-tailed test) and systolic blood pressure. These results suggest that endogenous bradykinin contributes to the ramipril-associated alteration in renal lithium handling. Bradykinin B2 receptor-mediated vasodilation seems to be involved.

Inhibitory effect of reactive oxygen species on angiotensin I-converting enzyme (kininase II)

1. Somatic angiotensin I-converting enzyme (ACE) is a protein that contains two similar domains (N- and C-terminal), each possessing an active site. We have examined the effects of a generator of hydroxyl radicals (g*OH: 2,2'-azo-bis(2-amidinopropane)) and hydrogen peroxide (H2O2) on ACE using an in vitro approach. 2. The generator of hydroxyl radicals inactivated ACE in a time (2-6 h)- and concentration (0.3-3 mmol/L)-dependent manner at 37 degrees C. When ACE was coincubated for 4 h with g*OH (3 mmol/L), its activity decreased by 70%. Addition of dimethylthiourea or mannitol + methionine, two *OH scavengers, resulted in a significant protection of ACE activity. Mercaptoethanol and dithiotreitol, two thiol-reducing agents, also efficiently protected ACE activity. 3. The hydrolysis of two natural and domain-specific substrates was explored. The hydrolysis of angiotensin I, preferentially cleaved by the C-domain, was significantly inhibited (57-58%) after 4 h exposure to g*OH (0.3-1 mmol/L). Under the same conditions of exposure, the hydrolysis of N-acetyl-Ser-Asp-Lys-Pro, a specific substrate for the N-domain, was only slightly inhibited by 1 mmol/L g*OH. 4. Hydrogen peroxide, another source of *OH, was used. After exposure to H2O2 (3 mmol/L; 4 h), an 89% decrease in ACE activity was observed. Pretreatment with the iron chelator deferoxamine (1 mmol/L) attenuated H2O2-mediated ACE inactivation, demonstrating that the effect of H2O2 was partly due to its conversion into *OH (Fenton reaction). 5. In summary, our findings demonstrate that g*OH and H2O2 inhibit ACE activity and suggest a preferential action of g*OH on the C-domain of the enzyme.

Vascular catabolism of bradykinin in the isolated perfused rat kidney

Kinins in the circulation are rapidly metabolized by several different peptidases. The purpose of this study was to evaluate the contribution of membrane-bound peptidases to kinin metabolism in the renal circulation. Experiments were performed in vitro, in isolated rat kidneys perfused at a constant flow rate (8 ml/min) with Tyrode's solution. The effects of peptidase inhibitors were evaluated on the functional vasodilator response caused by bradykinin (30 nM) or [Tyr(Me)(8)]bradykinin (10 nM) via activation of bradykinin B2 receptors in kidneys precontracted with prostaglandin F2alpha. Angiotensin converting enzyme inhibitors, enalaprilat (3 microM), ramiprilat (1 microM) or lisinopril (1 microM), increased the bradykinin-induced renal vasodilation by 40% or more. Inhibitors of neutral endopeptidase (thiorphan or phosphoramidon, 10 microM), basic carboxypeptidase (DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid or MGTPA, 10 microM) and aminopeptidase P (apstatin, 20 microM) however did not enhance the renal vasodilator response elicited by kinins, whatever tested alone or in the presence of lisinopril. These findings indicate that angiotensin converting enzyme is the major peptidase whose inhibition potentiates the renal bradykinin B2 receptor mediated vasodilator response of kinins. The relative contribution in this potentiation of inhibition of kinin inactivation and of cross-talk of angiotensin converting enzyme with bradykinin B2 receptor remains however to be clarified.

[Sodium intake and hypertension]

The guidelines for hypertension treatment recommend a reduction of dietary sodium intake. There is still a controversy, few studies showing an inverse correlation between cardiovascular morbidity and salt intake, about the benefit expected from a reduction of sodium intake on the blood pressure level. This controversy is explained by the great variability of the pressure response when individuals are exposed to different sodium intakes, diet and environmental factors playing an additional role of variability. Salt sensitivity is more frequent in hypertensive, obese and in elderly patients. There is no harm to reduce salt overtake moreover normalisation of the dietary sodium intake has clearly demonstrated its ability to reduce hypertension complications in patients at high cardiovascular risks.

Vasopressin does not effect hypertension caused by long-term nitric oxide inhibition

Nitric oxide attenuates both vasopressin-induced vasoconstriction and vasopressin release. We tested whether hypertension and renal dysfunction elicited by chronic inhibition of nitric oxide (NO) synthesis using N(G)-nitro-L-arginine (L-NNA) could be mediated in part by vasopressin V(1A) receptors. Male rats were treated orally for 6 weeks with L-NNA (15 mg/kg per day), a nonpeptide V(1A) receptor antagonist (2S)-1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3, 4-dimethoxybenzene-sulfonyl)-3-hydroxy-2, 3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide (SR 49059, 30 mg/kg per day), or a combination of SR 49059 and L-NNA (same doses), or they received no treatment. Both drugs were added to the food. Measurements were performed in conscious rats (urine collection in metabolic cages, tail-cuff arterial pressure) and at the end of the study in anesthetized rats (clearance measurements). L-NNA produced sustained hypertension, decreased glomerular filtration rate, and increased renal vascular resistance, plasma renin activity, and urinary albumin excretion. SR 49059 had no effect per se on these parameters and also did not attenuate the hypertension and renal dysfunction induced by L-NNA. Surprisingly, SR 49059 potentiated L-NNA-induced hypertension at the end of the 6-week treatment. However, the blood pressure response and the renal and mesenteric vasoconstriction elicited by exogenous vasopressin were attenuated in rats treated with SR 49059. L-NNA did not change plasma vasopressin concentration or 24-hour urinary vasopressin excretion. Our findings suggest that activation of vasopressin V(1A) receptors does not contribute to the hypertension and renal dysfunction induced by chronic NO synthesis inhibition. They also document unchanged plasma vasopressin concentration in NO-deficient hypertension.

Cardiovascular and renal effects of central administration of a mineralocorticoid receptor antagonist in conscious female rats

In a previous study we showed that in normotensive male rats brain mineralocorticoid receptor blockade induced a long lasting decrease in blood pressure associated with increased urinary excretion of water and electrolytes. Here, we report the effect of intracerebroventricular injection of a mineralocorticoid receptor antagonist (RU28318; 3,3-oxo-7 propyl-17-hydroxy-androstan-4-en-17yl-propionic acid lactone) on cardiovascular and renal function in female rats. Compared with male rats, females are less sensitive to brain mineralocorticoid receptor blockade. Administration of RU28318 (10 ng, 100 ng) caused a significant decrease in systolic blood pressure (10-12.5%) only at 8 h after injection. An increased urinary excretion of water (about 160%) and electrolytes (about 175%) during the first 8 h after the injection was observed in the 100 ng RU28318 treated group. Heart rate, food intake and water consumption were not affected at either dose. In conclusion, in conscious female rats, brain mineralocorticoid receptors participate in blood pressure and renal function control.

Brain mineralocorticoid receptor control of blood pressure and kidney function in normotensive rats

Brain mineralocorticoid receptors appear to contribute to mineralocorticoid hypertension and may be involved in blood pressure control in normotensive rats. We examined the effect of blockade of central mineralocorticoid receptors with the use of a selective antagonist (RU28318) on cardiovascular and renal function in conscious normotensive rats. The contribution of renal innervation was evaluated in rats with bilaterally denervated kidneys. Young adult, male Wistar rats were trained for systolic blood pressure measurement by a tail sphygmographic method and accustomed to metabolic cages for collection of urine. One week before experimentation, an intracerebroventricular cannula was implanted. Systolic blood pressure was diminished 30 minutes after an intracerebroventricular dose of 10 ng of RU28318. The effect was maximal at 8 hours and was still present after 24 hours. Blood pressure returned to the basal level by 48 hours. During the period 0 to 8 hours after intracerebroventricular injection, rats treated with the antagonist showed an increase in diuresis and urinary electrolyte excretion. No significant effect on plasma renin activity, measured 8 and 30 hours after administration of RU28318, was observed. In denervated rats, the decrease in systolic blood pressure after administration of RU28318 was reduced. The difference was statistically significant compared with controls at 2 hours but not at 8 hours, and blood pressure returned to the basal value by 24 hours. The increases in diuresis and urinary electrolyte excretion induced by RU28318 were abolished in denervated rats. These results show that brain mineralocorticoid receptors are involved in blood pressure regulation and kidney function homeostasis in conscious normotensive rats. The renal nerves appear to participate in the brain mineralocorticoid receptor control of blood pressure.

[Diuretic resistance: mechanisms and therapeutic possibilities]

The diuretics, with the exception of spironolactone, act on the luminal (or apical) surface of the tubular cells of different segments of the nephron. In order to act, they must be secreted into the tubular lumen. This transfer of the drug to its site of action may be blocked by decreased renal blood flow, the saturation of the systems of tubular transport or fixation to the albumin present in the primary urine. All these pharmacokinetic abnormalities (observed in renal failure or the nephrotic syndrome) lead to diuretic resistance. Increasing the dosage, the repetition, intravenous administration, even as an infusion, are possible solutions. Resistance may be observed in the absence of pharmacokinetic abnormalities: in these cases, there is an abnormal response of the tubular cells to otherwise effective diuretic concentrations, or the activation of homeostatic mechanisms leading to sodium retention and preventing negativisation of the salt and water balance. These situations are often associated in cardiac failure or cirrhosis with oedema. Increasing the dosage is not a logical solution, but increasing the frequency of administration may be helpful. The importance of secondary hyperaldosteronism in cirrhotic oedema makes spironolactone the treatment of choice. In all cases, the addition of two mechanisms of inhibition of tubular reabsorption of sodium at different sites in the nephron often results in an effective diuresis: usually, this implies the addition of a thiazide (e.g. hydrochlorothiazide) to an initial prescription of a loop diuretic.

[Modulation by nitric oxide of vasopressin induced renal vasoconstriction varies with perfusate viscosity in the isolated rat kidney]

Previously we reported that AVP is a potent vasoconstrictor in the TYRODE's perfused rat kidney. In vivo however AVP elicited only minor effects on renal blood flow. We hypothetized that differences in shear stress, particularly related to differences in viscosity could be involved. In this study, we investigate the role of perfusate viscosity in the modulation of AVP-induced renal vasoconstriction by NO. Experiments were performed in kidneys isolated from male Sprague-Dawley rats (220 g). Kidneys were perfused at a constant flow of 8 mL/min, in a recirculating system, with TYRODE's solutions supplemented with 6% bovin serum albumin (BSA) or 4.7% Ficoll 400 (Ficoll). The viscosities relative to water were respectively of 1.33 (BSA), 2.32 (Ficoll) and 1.03 (TYRODE). Concentration-response curves to AVP were constructed in the absence or presence of 100 microM N omega-nitro-L-arginine (L-NA), an inhibitor of NO synthase, and compared to those obtained in kidneys perfused with TYRODE's solution. AVP elicited a concentration-dependent renal vasoconstriction, with a progressive shift of the curves to the right and a small decrease in the maximum response when the kidneys were perfused with perfusates of increasing viscosities: logEC50 = -9.9 +/- 0.1 (TYRODE, n = 14), -9.7 +/- 0.1 (BSA, n = 5), -9.0 +/- 0.1 (Ficoll, n = 5) (m +/- e.s.m. Anova, p < 0.001); Emax = 34 +/- 1, 31 +/- 2 and 26 +/- 3 mmHg/mL/min (Anova, p < 0.001). L-NA abolished the differences between kidneys perfused with solutions of different viscosities in logEC50 for vasopressin (10.3 +/- 0.1, 10.4 +/- 0.1 and 10.5 +/- 0.1, n = 5-11, Anova, NS) but did not affect Emax values. In conclusion, present results show that 1) AVP-induced renal vasoconstriction is modulated according to the viscosity of perfusate and 2) NO is involved in this effect. Viscosity, a major determinant of shear stress, should be considered in hemodynamic studies performed on isolated kidneys.

[Effects of hydroxyl radicals on purified angiotensin I converting enzyme]

Somatic angiotensin-converting enzyme (ACE) is a protein which contains two similar domains (N and C), each possessing a functional active site. The relationship between ACE, its natural substrates and oxygen free radicals is starting to be explored. On one hand, superoxide anions production is induced by angiotensin II and on the other hand, activated polynuclear neutrophils, through free radicals generation, alter endothelial ACE activity. In this study, we examined the impact of hydroxyl radicals (.OH) on purified ACE. .OH were produced using a generator: 2,2'-azo-bis 2-amidinopropane (GRH) provided by Lara-Spiral (Fr). GRH (3 mM), in a time-dependent fashion, inhibited ACE activity. When ACE was co-incubated for 4 h with GRH, its activity decreased by 70%. Addition of dimethylthiourea (DMTU: 0.03 to 1 mM) or mannitol + methionine (20/10 mM), two sets of .OH scavengers, produced a dose-dependent protection on ACE activity. To examine whether oxidation of thiol groups in the ACE molecule could be involved in the action of GRH, the effects of thiol reducing agents: mercaptoethanol and dithiotreitol (DTT) were investigated. These compounds produced a dose-dependent and significant protection; with 100% protection at 0.2 and 0.3 mM for mercaptoethanol and at 0.1 mM for DTT. The hydrolysis of two natural and domain-specific substrates were also explored. The hydrolysis of angiotensin I preferentially cleaved by the C domain was significantly (p < 0.01) inhibited by 57, 58 and 69% in contact with 0.3, 1 and 3 mM GRH [in nmol angio II formed/min/nmol of ACE, n = 4; 35.9 +/- 0.6 (control), 15.5 +/- 2.8 (GRH : 0.3 mM), 15.1 +/- 0.5 (1), 10.9 +/- 0.6 (3)]. The hydrolysis of the hemoregulatory peptide (hp), preferential substrate for the N domain was not affected by GRH at 0.3 mM and inhibited by 28% (not significant) by 1 mM GRH [in nmol ph hydrolized/min/nmol ACE, n = 4; 12.6 +/- 1.9 (control), 14.9 (GRH : 0.3 mM), 8.3 +/- 4.0 (1). These results demonstrated that .OH affect ACE activity and could suggest a privileged impact of GRH on the C domain. The precise sites of action of .OH remain unknown. The Cys residues near the active centers, by forming disulphide bridges during the oxidation could be of critical importance. Further studies will be needed to determine whether oxidative stress again ACE can be involved in the genesis of inflammatory vascular pathologies.

[Aldosterone antagonists: new pharmacologic prospects]

The pharmacology of the mineralocorticoid receptor antagonist spironolactone and analogues is reviewed in the light of recent discoveries regarding the primary structure of corticosteroid receptors and the different isoforms of the enzyme 11 beta-hydroxysteroid dehydrogenase. The type 2 isoform of this enzyme functions in some tissues to keep the aldosterone receptor activation specific, i.e. it allows stimulation by aldosterone while eliminating glucocorticoids such as cortisol and corticosterone. The type 2 isoform has been shown in the colon, hypothalamus, kidney, placenta and salivary gland. New clinical uses of aldosterone antagonists may be derived from these developments. Most prominent in this respect appear to be myocardial fibrosis and specific forms of hypertension with altered mineralocorticoid receptor functioning and deficiencies in the protection system of the receptor against glucocorticoids.

Plasma active renin, angiotensin I, and angiotensin II during pregnancy and in preeclampsia

OBJECTIVE

To evaluate the activity of the renin-angiotensin-aldosterone system in the circulation during the three trimesters of normal pregnancy and in women with preeclampsia.

METHODS

Normal pregnant volunteers (n = 7) were studied throughout pregnancy, and women with preeclampsia (n = 8) were studied in the third trimester. Plasma active renin and aldosterone were measured by radioimmunoassay. Angiotensin I and angiotensin II were determined by radioimmunoassay after separation of the peptides by high-performance liquid chromatography.

RESULTS

Active renin concentration increased in the first trimester of normal pregnancy, whereas angiotensin I, angiotensin II, and aldosterone remained at a level comparable to the postpartum values. Highest activity of the renin-angiotensin-aldosterone system was observed during the third trimester with increased levels of angiotensin I, angiotensin II, and aldosterone. In contrast, in patients with preeclampsia, despite a slight increase of active renin levels, the other parameters of the renin-angiotensin-aldosterone system were low compared with the third trimester of normal pregnancy and were comparable to postpartum data.

CONCLUSION

Our results suggest that during the first trimester of normal pregnancy, active renin concentration in the plasma is increased and that renin is not the factor that limits angiotensin II synthesis. These results also confirm decreased activity of the renin-angiotensin-aldosterone system in preeclampsia. This could contribute to the diminished hemodynamic control observed in pregnant women developing preeclampsia.

[Renal tissue angiotensins during converting enzyme inhibition of angiotensin I in spontaneously hypertensive rat]

To compare the effects of an angiotensin-converting enzyme inhibitor on circulating and tissue renin-angiotensin system, we measured different renin-angiotensin system parameters during the first day of treatment (Day 1) as well as after two weeks of treatment (Day 14). Ramipril was given orally once daily to adult male spontaneously hypertensive rats. Renin activity, angiotensin-converting enzyme activity and levels of angiotensin I and angiotensin II in the plasma, renal cortex and renal medullar were assessed at Day 1 and Day 14 of the treatment. In the plasma, both renin activity and angiotensin I increased 10 to 15 fold one to four hours after acute as well as at Day 14 of ramipril treatment and then returned to basal values within 24 hours. Plasma angiotensin II levels were not significantly decreased at Day 1 or Day 14. The decrease in the angiotensin II/angiotensin I ratio suggested a sustained inhibition of plasma angiotensin-converting enzyme at Day 14. In the renal cortex and medulla, a clearly different pattern was observed: in ramipril treated rats, renin activity in the renal cortex and medulla did not change at Day 1 but at Day 14 we observed a slight and sustained increase in renin activity. Despite very high basal levels of renin activity, angiotensin I levels in the renal cortex were comparable to those in the plasma. The angiotensin I level increased only one-fold one hour after ramipril intake at Day 1 and Day 14. This suggests that angiotensinogen may have a limiting role in the synthesis of angiotensin I in the kidney. Angiotensin II levels were slightly higher in the renal cortex and medulla than in the plasma suggesting local synthesis of the peptide. In the kidney, angiotensin II levels decreased one and four hours after the acute or prolonged ramipril treatment and the angiotensin II/angiotensin I ratio was reduced at the same time. Our results show that the responses of the plasma and kidney components of the renin-angiotensin system to angiotensin-converting enzyme inhibition are different in the plasma and the kidney suggesting that the circulating and tissue renin-angiotensin system are at least in part independent.

[Renal vascular responses of bradykinin in the isolated rat kidney]

Kinins, by an autocrine or paracrine hormonal action, are potent modulators of regional vasomotricity. Their effects on the renal circulation are not well defined. The aim of this study was to analyse the renal vascular response induced by bradykinin, to precise the type(s) of receptor involved and to evaluate the contribution of various peptidases in the local catabolism of the kinin. Experiments were performed on the isolated rat kidney, perfused in an open circuit, at a constant flow of 8 mL/min, with a Tyrode's solution. Vasodilator responses were evaluated after renal vascular tone had been restored by a continuous perfusion with prostaglandin F2 alpha. Infusion of bradykinin (0.1-30 nM) induced a concentration-dependent renal vasorelaxation. A maximal response of 39.5 +/- 2.8% (n = 32) reversion of the tone induced by prostaglandin F2 alpha (about 50% of the maximal response induced by acetylcholine on the same kidneys) was obtained at 30 nM. Bradykinin-induced vasodilatation was completely inhibited by HOE 140 (10 nM), a selective bradykinin B2 receptor antagonist. At a supramaximal concentration of 300 nM, bradykinin-induced vasorelaxation was modulated by a concomitant vasoconstriction. A concentration-dependent vasoconstriction was also obtained with desArg9 bradykinin (1-8 microM), a selective agonist of the bradykinin B1 receptor. The inhibition of neutral endopeptidase by phosphoramidon (10 microM) or the inhibition of carboxypeptidase M by MGTPA (10 microM) did not modify the bradykinin-induced renal vasorelaxation. On the other hand, the inhibition of angiotensin I converting enzyme by lisinopril (1 microM) potentiated by about 32% the vasorelaxant response induced by 30 nM bradykinin (52.3 +/- 11.8% relaxation, n = 5, p < 0.05). Present results demonstrate that 1) bradykinin primarily evokes B2 receptor-linked renal vasodilatation, 2) bradykinin B1 receptors appear also to be present on the rat renal vasculature and 3) angiotensin 1 converting enzyme contributes to the local vascular catabolism of the kinin.

Renal tissue angiotensins during converting enzyme inhibition in the spontaneously hypertensive rat

To compare the effects of an angiotensin-converting enzyme inhibitor on circulating and tissue renin-angiotensin system (RAS), we measured different RAS parameters during the first day of treatment (Day1) as well as after two weeks of treatment (Day14). Ramipril was given orally once daily to adult male spontaneously hypertensive rats (SHR). Renin activity (RA), angiotensin converting enzyme (ACE) activity and levels of angiotensin I (ang I) and angiotensin II (ang II) in the plasma, renal cortex and renal medulla were assessed at Day1 and Day14 of the treatment. In the plasma, both RA and ang I increased 10 to 15 fold one to four hours after acute as well as at Day14 of ramipril treatment and then returned to basal values within 24 hours. Plasma ang II levels were not significantly decreased at Day1 or Day14. The decrease in the ang II/ang I ratio suggested a sustained inhibition of plasma ACE at Day14. In the renal cortex and medulla, a clearly different pattern was observed: in ramipril treated rats, RA in the renal cortex and medulla did not change at Day1 but at Day14 we observed a slight and sustained increase in RA. Despite very high basal levels of RA, ang I levels in the renal cortex were comparable to those in the plasma. The ang I level increased only one-fold one hour after ramipril intake at Day1 and Day14. This suggests that angiotensinogen may have a limiting role in the synthesis of ang I in the kidney. Ang II levels were slightly higher in the renal cortex and medulla than in the plasma suggesting local synthesis of the peptide. In the kidney, ang II levels decreased one and four hours after the acute or prolonged ramipril treatment and the ang II/ang I ratio was reduced at the same time. Our results show that the responses of the plasma and kidney components of the RAS to ACE inhibition are different in the plasma and the kidney suggesting that the circulating and tissue RAS are at least in part independent.

Vascular effects of [Arg8]vasopressin in the isolated perfused rat kidney

The renal vascular effects of [Arg8]vasopressin (vasopressin) were investigated in the isolated perfused rat kidney. Vasopressin (0.01-3 nM) elicited a dose-dependent vasoconstriction in kidneys from Sprague Dawley rats, with a EC50 value of 0.206 +/- 0.044 nM. Inhibition of nitric oxide synthase by N omega-nitro-L-arginine (100 microM) shifted the vasopressin-induced vasoconstrictor response curve to the left. Inhibition of cyclooxygenase by indomethacin (10 or 30 microM) blunted the constriction induced by low concentrations of the peptide. Vasopressin, like angiotensin II but not noradrenaline, induced tachyphylaxis, SR 49059 ((2S)1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3,4-dimethoxybenzene- sulfonyl)-3-hydroxy-2,3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2- carboxamide) (1-30 nM), a new potent and selective non-peptide vasopressin V1A receptor antagonist, shifted the concentration-response curve for vasopressin to the right without decreasing the maximum contraction. Antagonism became competitive with a pA2 value (+/- S.D.) of 9.72 +/- 0.20 during inhibition of nitric oxide release. [Mpa1,D-Arg8]Vasopressin (desmopressin; 0.1-100 nM), or vasopressin (0.01-1 nM) after blockade of the vasopressin V1A receptor by SR 49059, induced no vasopressin V2 receptor-related renal relaxation in kidneys with vascular tone previously restored by noradrenaline or prostaglandin F2 alpha. These findings indicate that in the isolated perfused rat kidney vasopressin is a potent renal vasoconstrictor. The constriction depends on activation of smooth muscle vasopressin V1A receptors and is modulated by endothelial nitric oxide but not by prostacyclin or vasopressin V2 receptor-related vasodilation.

Interruption of prolonged ramipril treatment in hypertensive patients: effects on the renin-angiotensin system

The increase in renin secretion and the induction of the converting enzyme (ACE) observed during treatment by ACE inhibitors (CEIs) could result in increased angiotensin II (ang II) synthesis when the treatment is stopped. The object of this study was to compare changes in the components of the renin-angiotensin system with changes in arterial pressure in hypertensives, following the cessation of long-term ramipril treatment. Twenty hypertensives, treated for at least three months with ramipril, in monotherapy for the last three weeks, were randomly allocated to two parallel groups and received for fifteen days, on a double-bind basis, either a placebo (withdrawal group W, n = 12) or ramipril at the previous doses (treated group T, n = 8). Blood pressure was measured using four different techniques. The active renin (AR), angiotensinogen, angiotensin I (ang I), angiotensin II (ang II) and aldosterone plasma concentrations were measured, as was plasma angiotensin I converting enzyme (ACE) activity in vitro (colorimetric and fluorimetric method) and in vivo (the ang II/ang I ratio). The biological effects of cessation of long-term ramipril treatment in hypertensives were a decline in AR and angiotensin I concentrations, an increase in ACE activity and no significant changes in angiotensinogen, angiotensin II and aldosterone levels. Fifteen days after withdrawal, the different parameters of the renin-angiotensin system appear to have returned to basal value. A slow rise in blood pressure was also observed but no rebound increase was noted during the 15 days neither in angiotensin II levels nor in blood pressure. Following the cessation of prolonged ramipril treatment, in vivo converting enzyme inhibition disappears slowly, probably on account of the slow tight binding inhibitor properties of ramiprilat, the active metabolite of this CEI. The gradual decline in AF, plasma levels, together with the prolonged ACE inhibition as measured in vivo by the ang II/ang I ratio, explains the absence of a rise in ang II synthesis.

Endothelium-dependent relaxation in the isolated rat kidney: impairment by cyclosporine A

The therapeutical use of cyclosporine A (CsA) is hampered by the development of nephrotoxicity characterized by a marked increase in renal vascular resistance (RVR). We investigated vascular functions in kidneys of rats treated with CsA. The ex vivo vascular reactivity of kidneys from control rats and animals treated subacutely with CsA [50 mg/kg/day subcutaneously (s.c.) for 16-21 days] or an olive oil vehicle (1 ml/kg) was analyzed in male Wistar rats. The right kidney was isolated and perfused with Tyrode's or Krebs solution in an open circuit. The effects of acetylcholine (Ach), fenoldopam (FEN), and sodium nitroprusside (SNP) on norepinephrine (NE) preconstricted kidneys were studied. In control kidneys (untreated or vehicle-treated), Ach induced a relaxation (EC50 = 0.56 +/- 0.05 x 10(-9)M; Emax = 88.2 +/- 2.1% decrease in the vascular tone restored by NE) which was endothelium-dependent [near-complete abolition after treatment with a detergent, 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propane-sulfonate (CHAPS) treatment] but only partially inhibited by indomethacin (EC50 = 1.71 +/- 0.39 x 10(-9)M, p < 0.05; Emax = 87.1 +/- 4.9%, NS) or indomethacin with NG-nitro-L-arginine methyl ester (L-NAME: EC50 = 1.04 +/- 0.38 x 10(-9)M, NS; Emax = 63.8 +/- 2.5%, p < 0.01). CsA treatment induced a marked decrease in creatinine clearance and natriuresis measured in vivo but had no effect on systolic blood pressure (SBP). In CsA-treated rats, Ach-induced renal relaxation was partially blunted (EC50 = 1.88 +/- 0.34 x 10(-9)M, p < 0.01; Emax = 82.8 +/- 4.6, NS), with both a defect in prostaglandin (PG) and nitric oxide (NO)-related responses. CsA treatment had no effect on endothelium-independent relaxations induced by FEN and SNP. These results show that subacute CsA treatment selectively impairs renal endothelium-dependent relaxation related to PGs and NO release.

[Relation between plasma renin level and antihypertensive response to nicardipine]

The antihypertensive efficacy of calcium antagonists could depend on the concentration of circulating renin. To investigate this hypothesis, 102 hypertensive men or women were included in this study. After an initial 2 week placebo period, the patients were administered slow-release nicardipine, 50 mg twice a day for twelve weeks. The blood pressures were measured with a mercury sphygmomanometer at inclusion (S2) and after 12 weeks of treatment (S14), in addition to home automeasure during the week before inclusion and the two weeks preceding the final visit. The plasma renin activity (RA) was measured at S2 and S14. Its value at inclusion was used to differentiate patients with low renin (< or = 11 ng/l) from those with normal (> 11 < or = 17 ng/l) or high renin activity (> 17 ng/l). The blood pressure measured by sphygmomanometer or automeasure was significantly lower at the end of the active treatment period (SBP: -8 mmHg; DBP: -9.5 mmHg; and SBP: -5.8 mmHg; DBP: -5.7 mmHg respectively); the reduction in blood pressure was significantly higher in the group with low RA than in the group with high RA. The reductions in SBP measured in the morning and evening and in DBP measured in the morning were significantly greater in the group with low RA than in the group with high RA. The reduction of SBP measured in the morning at midday, and in the evening was correlated to the basal value of RA. Mild side effects were observed in 20 patients leading to the interruption of treatment in 11 cases because of headache. The best antihypertensive response is observed in patients with low plasma RA. This could explain the good response to calcium antagonists usually observed in elderly hypertensives.

Ramipril-induced decrease in renal lithium excretion in the rat

1. The interaction of ramipril, an inhibitor of angiotensin I converting enzyme, with renal lithium handling was analysed in conscious normotensive Wistar rats and compared with the known increase in renal tubular lithium reabsorption induced by the non-steroidal anti-inflammatory drug, indomethacin. 2. The rats were treated for five days with ramipril (1 mg kg-1 day-1 orally), indomethacin (2.5 mg kg-1 day-1 intramuscularly) or their solvents. Lithium chloride (16.7 mg kg-1 intraperitonealy) was given as a single dose on the fifth day and renal functions were measured. 3. Ramipril induced a decrease in renal lithium clearance which was correlated with the decrease in the quantity of filtered lithium and the increase in the tubular fractional reabsorption of the metal. Ramipril also reduced the systolic blood pressure of the rats by about 15 mmHg. 4. In the absence of any effect on creatinine clearance or systolic blood pressure, indomethacin increased renal fractional lithium reabsorption and led to an increase in plasma lithium levels, as previously reported by our group. 5. In conclusions, our results indicate that ramipril decreases renal lithium excretion in Wistar rats, when given orally at a dose of 1 mg kg-1 day-1 over five days.

Absence of a losartan interaction with renal lithium excretion in the rat

1. The interaction of losartan, a non-peptide specific AT1 receptor antagonist with the renal handling of lithium was analysed in conscious normotensive Wistar rats and compared with the known increase in renal tubular lithium reabsorption induced by the non-steroidal anti-inflammatory drug, indomethacin. 2. The rats were treated for five days with losartan (10 mg kg-1 day-1, orally), indomethacin (2.5 mg kg-1 day-1, intramuscularly) or their solvents. Lithium chloride (16.7 mg kg-1, i.p.) was given as a single dose on the fifth day; renal functions were then measured. 3. Indomethacin, in the absence of any effect on creatinine clearance, increased renal fractional lithium reabsorption and led to an increase in plasma lithium levels. 4. Losartan did not modify renal lithium handling and its plasma level. No change was observed in renal lithium clearance, the quantity of filtered lithium or the fractional reabsorption of the metal. As expected, losartan had no effect on systolic blood pressure in normotensive rats. 5. In conclusion, our results indicate that losartan, when given orally in the rat at a dose of 10 mg kg-1 day-1 over five days, does not modify renal lithium handling. They suggest that blockade of the angiotensin II receptors does not interfere with renal lithium reabsorption, which occurs mainly at a proximal tubular site.

Stereoselective renal effects of the loop diuretic ozolinone in the anesthetized dog

The renal effects of i.v. injections of (+/-)-ozolinone, its enantiomers (-)-ozolinone and (+)-ozolinone and its prodrug (+/-)-etozoline, were compared with those of furosemide, in pentobarbital anesthetized dogs. Renal blood flow (electromagnetic flow-meter) and glomerular filtration rate (polyfructosan clearance) were assessed on the left denervated kidney together with renin secretion and urinary electrolyte excretion. (-)-Ozolinone (15.5 mg/kg i.v.) behaves as a stereoselective loop diuretic equipotent to 20 mg/kg of furosemide and 45 mg/kg of (+/-)-ozolinone; (+)-ozolinone induced only minor salidiuretic effects. Both ozolinone enantiomers markedly increased the renal blood flow and decreased the filtration fraction, suggesting that the vosodilating effect predominates on the efferent glomerular arterioles. (-)-Ozolinone also induced an acute rise in renin secretion. The inhibition of prostaglandin synthesis (indomethacin or meclofenamate) prevented renin hypersecretion in response to (-)-ozolinone and modified its salidiuretic effects but had no effect on the vascular response. The inhibition of the kallikrein-kinin system by aprotinin had no effect on the overall renal response to (-)-ozolinone. The inhibition of the renin-angiotensin system by captopril decreased blood pressure, prolonged the (-)-ozolinone-induced decrease in renal vascular resistance and increased renin secretion. Our results demonstrate that the loop diuretic, ozolinone, induces stereoselective and prostaglandin-dependent renin secretion, which is involved in the regulation of intra-renal hemodynamics.

Pathophysiological role of dopamine in the kidney: effects in diabetes mellitus and after contralateral nephrectomy

Both insulin-dependent diabetes mellitus (IDDM) and unilateral nephrectomy (UNX) are associated with an increase in the glomerular filtration rate. Glomerular hyperfiltration has been linked to intraglomerular hypertension in both conditions, although it has only been linked to the development of nephropathy in diabetes. In this study, we examined the possibility of preventing diabetic nephropathy through early dopamine (DA) prodrugs treatment and we also investigated the participation of endogenous DA in the acute functional adaptation of the remaining kidney after UNX. In an animal model of IDDM (steptozotocin-treated Wistar rats), the early increase in the glomerular filtration rate was prevented by treatment with DA prodrugs (L-dopa or gludopa), an effect which was mimicked by fenoldopam (a D1 agonist) and suppressed by carbidopa and SCH 23390 (a D1 antagonist). An increase in endorenal DA synthesis and the subsequent stimulation of vascular D1 receptors appears to prevent early glomerular hyperfiltration in diabetic rats. However, in a long-term study lasting more than one year, streptozotocin-diabetic Wistar rats (unlike to diabetic Munich Wistar rats) failed to develop overt nephropathy characterized by albuminuria and systemic hypertension. During long-term treatment of diabetic rats with L-dopa, the renal availability of DA was diminished. The acute adaptation of the remaining kidney to UNX took the form of an early transient pressor effect with a moderate increase in the glomerular filtration rate and renal blood flow, and a marked decrease in tubular sodium reabsorption. SCH 23390 suppressed the hemodynamic and tubular responses to UNX, suggesting that endogenous DA plays a key role.

[Ramipril and cardiac and renal angiotensin converting enzyme]

The role of the angiotensin converting enzyme (ACE) in the regulation of local synthesis of angiotensin II has not been clearly defined. The authors investigated the local factors which might orientate the effects of ACE inhibitors to particular organs in the Wistar rat. The in vivo study of the effects of low doses of ramipril on the myocardium showed that cardiac ACE was significantly inhibited by the non-antihypertensive dose of 0.01 mg/kg whereas the inhibition only occurred from doses higher than 0.1 mg/kg in the other tissues studied. In the kidney: the affinity of 3H-ramiprilate for the brush borders of the proximal tubular cells was increased by high concentrations of chloride ions as observed in the renal parenchyma, the presence of esterases makes local activation of ramipril (diester) into ramiprilate (active diacid) possible, prolonged treatment with ramipril leads to a lowering of the concentration of ACE in the brush border of the proximal tubular cells, verified after the elimination of the ACE inhibitor fixed on the tissue. These data indicate that the myocardium and the kidney could be privileged targets of the action of ramipril.

Effects of triiodothyronine and dexamethasone on plasma and tissue angiotensin converting enzyme in the rat

In order to identify tissue specific regulation of angiotensin converting enzyme (ACE), the effects of dexamethasone (0.04 mg sc per day for 7 days) and triiodothyronine (T3) (0.5 mg/kg sc per day for 10 days) on ACE activity were investigated in different tissues in male Wistar rats. ACE activity was measured by fluorimetry in the plasma, heart, lung and kidney. In the kidney, ACE activity was measured in the medulla, cortex and brush border of proximal tubular cells and 3H-ramiprilat binding was used to characterise the changes in brush border ACE activity. Dexamethasone elicited a significant increase in lung ACE activity and a significant decrease in plasma ACE activity, but did not alter enzyme activity in the other tissues studied. T3 produced a significant decrease in lung ACE activity and an increase in ACE activity in the plasma and heart. In the kidney, ACE activity was not modified in the medulla whereas in the cortex and brush border ACE activity was doubled. This increase in ACE activity corresponded to a similar increase in the maximum number of binding sites of 3H-ramiprilat, suggesting that the increase in activity corresponded to an increase in the ACE level. The increased heart and kidney ACE activity in response to T3 may contribute to the cardiovascular effects of thyroid hormones through increased local angiotensin II generation. These results show that under dexamethasone or T3, ACE activity can vary from one tissue to another, suggesting that the ACE regulatory mechanism acts differently in each tissue.

Short-term effects of quinapril and nifedipine on early renal changes in streptozotocin-induced diabetes in rats

The effects on renal function of quinapril, an angiotensin I converting enzyme (ACE) inhibitor, and of nifedipine, a dihydropyridine calcium antagonist, were studied in the early stages of diabetes in rats. Wistar rats received one injection of streptozotocin (STZ) to induce diabetes; the hyperglycaemia was then controlled with daily insulin therapy (2-3 units NPH insulin/rat). One week after STZ injection, rats were treated orally with quinapril (0.3 or 3 mg/kg/d) or nifedipine (30 mg/kg/day) for 1 week, after which renal functions were compared with those of untreated diabetic rats or non-diabetic control rats. At the end of these two weeks, diabetic rats had gained less weight and had developed renal hypertrophy and glomerular hyperfiltration (3.21 +/- 0.23 vs 2.36 +/- 0.09 ml/min for non-diabetic rats, mean +/- SEM, P < 0.01). Their urinary albumin excretion was higher, as was the urinary excretion of water, sodium, potassium, urea and glucose. One week treatment with quinapril or nifedipine had no significant effect on the increase in the glomerular filtration rate (respectively 2.97 +/- 0.18 and 2.99 +2- 0.15 ml/min). Quinapril and nifedipine differed with regard to their effects on urinary albumin excretion. Albuminuria was increased by nifedipine but not by quinapril (respectively 0.554 +/- 0.158 and 0.149 +/- 0.046 mg/day/100 g BW, P < 0.05). This difference between the effects of the dihydropyridine and the ACE inhibitor on albuminuria may be linked to different effects on the glomerular functions.

Effects of dietary protein and uninephrectomy on renal angiotensin converting enzyme activity in the rat

This study examines the effects of dietary protein and of uninephrectomy on angiotensin converting enzyme (ACE) in the normotensive rat, with particular regard to the kidney. Male Wistar Kyoto rats were fed isocaloric diets containing 5, 16 or 50% protein for three weeks. Other groups of rats were subjected to either left unilateral nephrectomy or sham operations, and the rats were killed eight days after surgery. ACE activity was measured in the kidney medulla, cortex, proximal tubule brush border membrane and in the plasma, heart and lung. Renal cortex and brush border ACE activity increased in parallel with protein intake, whereas plasma and lung ACE activity decreased; heart and kidney medulla ACE activity did not vary significantly. Uninephrectomy also led to a high increase in brush border ACE activity in the contralateral kidney, with no effect in the renal medulla or in the other tissues. The increase in ACE activity in the brush border membrane corresponded to a similar increase in the maximum number of binding sites of 3H-ramiprilat. This suggested that the increase in ACE activity corresponded to an increase in ACE concentration. The increase in renal tubular ACE activity could result in higher angiotensin II levels, and could consequently play a role in the modification of sodium reabsorption and cellular growth which occurs in the proximal tubule in these experimental models.

Plasma renin activity and changes in tissue angiotensin converting enzyme

OBJECTIVES

Recent evidence suggests that tissue generation of angiotensins I and II depends on the level of the plasma components of the renin-angiotensin system and on tissue-specific processes. The present study was undertaken to clarify the possible relationship between plasma renin activity (PRA) and tissue angiotensin converting enzyme (ACE) activity in the heart, lung, kidney cortex and kidney medulla of Wistar-Kyoto rats. In the kidney cortex particular attention was focused on renal brush-border ACE.

METHODS

Different experimental models known to have opposite effects on PRA were used: changes in salt intake, deoxycorticosterone acetate (DOCA) with or without salt supplements, and the Goldblatt two-kidney, one clip (2-K,1C) model. Two weeks after the start of the experiments the rats were killed, and PRA, and plasma and tissue ACE activity, were measured.

RESULTS

At the end of the study the blood pressure in the treated rats was not significantly different from control. As expected, the PRA were highest in the 2-K,1C and depleted-salt groups and lowest in the DOCA, DOCA-salt and high-salt groups. ACE responses were different in different types of tissue, with no relationship between PRA and plasma or tissue ACE activity. For example, DOCA treatment led to increased ACE activity in the heart and the kidney only if the rats were maintained on a high salt intake. DOCA or salt alone failed to have this effect. In the 2-K,1C model the unclipped kidneys did not show any significant variation in ACE activity, but the clipped kidneys exhibited increased ACE activity compared with sham-operated rats. This increase, coupled with increased renal renin secretion, could play a role in the acceleration of local angiotensin II formation, and could thus initiate and sustain the development of hypertension in this model.

CONCLUSION

The present results show that variations in ACE activity were organ-specific and were not linked either to hypertension or to changes in PRA.

Vascular effects of loop diuretics: an in vivo and in vitro study in the rat

The vascular effects of loop diuretics were studied in two models designed to eliminate hemodynamic repercussions linked to sodium and water depletion: in vivo, in unilaterally nephrectomized rats with a contralateral uretero-venous shunt, and in vitro, in the isolated perfused rat kidney. In anesthetized rats, local vascular resistance was calculated from the simultaneous recording of blood pressure and renal, iliac and carotid blood flows (electromagnetic flowmeter, Skalar). Furosemide and piretanide (10 to 80 mg/kg i.v.) induced a comparable dose-dependent decrease in renal vascular resistance, which was not modified by reserpine and indomethacin pre-treatment. The iliac relaxing response was blunted by vasoconstriction, which disappeared after combined treatment with reserpine and indomethacin. The relaxation induced in the iliac and carotid vasculature persisted after bilateral nephrectomy. In vitro, the vasorelaxing effect of diuretics in isolated rat kidneys perfused in an open circuit was studied after vascular tone had been re-established by a continuous perfusion of PGF2 alpha. Furosemide, piretanide and ozolinone induced a concentration-dependent decrease in renal tone (EC50 = 0.47 x 10(-4) mol/l, 1.03 x 10(-4) mol/l and 2.07 x 10(-4) mol/l respectively) in Wistar rats. A similar response to piretanide was found in spontaneously hypertensive stroke-prone rats (EC50 = 0.32 x 10(-4) mol/l) and in their normotensive controls (EC50 = 0.74 x 10(-4) mol/l). Our results show that loop diuretics induce a direct relaxation in the renal, iliac and carotid vasculature. This vascular effect, which appears at relatively high concentrations of the drugs, is prostaglandin independent and persists after bilateral nephrectomy.

Effects of one-hour and one-week treatment with ramipril on plasma and renal brush border angiotensin converting enzyme in the rat

Prolonged treatment with an angiotensin converting enzyme inhibitor produces an induction of plasma angiotensin converting enzyme. Induction of angiotensin converting enzyme in tissues during prolonged treatment with an angiotensin converting enzyme inhibitor is less well documented. We compared the effects of 1 h and 1 week treatment with ramipril (0.1, 0.3, 1 mg/kg) on angiotensin converting enzyme activity in the plasma, renal cortex and renal brush border membrane of Wistar rats. As an increase in activity could be masked by the inhibition due to the presence of ramiprilat which is the active form of ramipril, we eliminated the ramiprilat present in renal cortex homogenates with EGTA during brush border preparation. The 1-h treatment with ramipril induced a dose-dependent inhibition of plasma and renal cortex angiotensin converting enzyme activity. The 1-week treatment with ramipril produced an increase in plasma angiotensin converting enzyme activity, whereas renal cortex angiotensin converting enzyme activity decreased. The decrease in angiotensin converting enzyme activity persisted in the brush border membrane after elimination of residual ramiprilat with EGTA. Our results show that prolonged ramipril treatment produces opposite responses in plasma and renal cortex angiotensin converting enzyme activity, suggesting that plasma and epithelial angiotensin converting enzymes are subject to specific local regulatory factors.

In vitro vascular reactivity of the rat utero-feto-placental unit

OBJECTIVE

To evaluate the vascular reactivity to vasoconstrictor drugs and the local role of angiotensin I-converting enzyme in the rat utero-feto-placental unit.

METHODS

The experiments were carried out in vitro on a new model of the isolated perfused uterine horn from 19 nonpregnant and 16 pregnant rats.

RESULTS

Norepinephrine, angiotensin II, and angiotensin I induced concentration-dependent vasoconstriction in non-pregnant uteri (50% effective concentration = 271 +/- 63, 9.9 +/- 3.7, and 1.7 +/- 0.8 x 10(-9) mol/L, respectively; n = 4-5, mean +/- standard error of the mean). In pregnant uteri, the maximum vasoconstrictor effects of norepinephrine (increase in perfusion pressure 132 +/- 6 versus 186 +/- 20 mmHg in pregnant and nonpregnant, respectively) and angiotensin II (37 +/- 9 versus 89 +/- 4 mmHg), but not angiotensin I, were significantly lower. The vasoconstrictor effect of angiotensin I was inhibited by saralasin, an antagonist of the angiotensin II receptors, and by ramiprilat, a converting-enzyme inhibitor.

CONCLUSION

The isolated perfused rat utero-feto-placental unit is a useful experimental model for studying uterine vascular reactivity during pregnancy. Our in vitro results confirm vascular refractoriness to norepinephrine and angiotensin II during pregnancy and demonstrate local angiotensin II synthesis in the rat uterine vascular bed.

[Plasma renin activity and angiotensin converting enzyme of renal brush borders]

The present experiment was undertaken to examine the relationship between plasma renin activity and the concentration of angiotensin converting enzyme (ACE) in plasma and renal brush border of Wistar Kyoto rats. Different experimental models known to have opposite effects on plasma renin activity were used: changes in salt intake, the deoxycorticosterone acetate (DOCA) and DOCA-salt models and the two-kidneys one clip (2K1C) model. Two weeks after the start of these experimental series, the rats were killed. At this time, blood pressure did not differ from control group, even in the 2K1C and DOCA-salt groups. As expected, PRAs were highest in the 2K1C and depleted salt groups and lowest in the DOCA, DOCA-salt and high salt groups. No relationship between this wide variation in PRA and change of ACE activity in both plasma and renal brush border could be observed. In the plasma, ACE activity in sodium-depleted rats was slightly decreased whereas no change occurred in the other models. In the kidney, DOCA treatment led to increased ACE activity in the brush border only if the animals were maintained on a high salt intake. DOCA or NaCl alone failed to have this effect. In the 2K1C model, the clipped kidneys exhibited increased brush border ACE activity whereas the unclipped kidneys did not show any significant variation in ACE activity, when compared to sham operated rats. In summary, on one hand these findings show that variations in ACE activity were linked neither to hypertension nor to changes in PRA.(ABSTRACT TRUNCATED AT 250 WORDS)

[Changing of renal endothelium-dependent vascular reactivity by cyclosporin A]

Clinical use of the immunosuppressant cyclosporine A (CSA) is hampered by its nephrotoxicity. The renal vascular resistance is increased, may be as a consequence of a deleterious effect of the drug on the vascular endothelial cell function. The renal effects of a subchronic treatment with CSA (50 mg/kg/d, sc, 18 days), or olive oil vehicule (1 ml/kg), were studied in normotensive male Wistar rats. Creatinine clearance was measured on 24 h urine collection before the right kidney of the animals was isolated and perfused in an open circuit at 6 ml/min with Tyrode's solution. Renal vasodilator responses to acetylcholine (ACH, 10(-10) to 10(-7) M) and sodium nitroprusside (NP, 3 x 10(-9) to 3 x 10(-6) M) were studied after reestablishment of a renal vascular tone by a continuous perfusion of noradrenaline (NA, 10(-7) M). ACH was more potent than NP to induce renal vasodilation (EC50 = 0.57 +/- 0.05 x 10(-9) M, n = 8, vs 3.42 +/- 0.29 x 10(-8) M, n = 5), but both drugs reversed the NA-induced vasoconstriction by near 90%. L-NAME (3 x 10(-5) M) had no effect on NP-induced renal relaxation but suppressed responses to low concentrations of ACH and decreased by half its Emax (47 +/- 17%).(ABSTRACT TRUNCATED AT 250 WORDS)

[Captopril test for detecting renal artery stenosis: changes in plasma renin concentration]

The aim of this study was to demonstrate the diagnostic value of changes in active renin concentration during the captopril test (measurements of plasmatic active renin concentrations, before 12.5 or 37.5 mg of captopril p.o., and 30 and 90 minutes after) in order to screen a significant renal artery stenosis. After a renal angiography, 88 hypertensive patients suspected of renovascular hypertension were classified according to the percentage of stenosis in the main renal artery: class I (< 30% - n = 50), II (30 to < 75% - n = 21), III (75 to < 90% - n = 8) and IV (90 to 100% - n = 11). The results of the captopril test were compared to those of renal angiography. The active renin before the test (basal AR), the greater increase in active renin after captopril (max AR), the difference between max AR and basal AR (DIF) and the active renin relative change after the test (RC) were compared in the 4 classes (ANOVA). There were no differences in diastolic blood pressure (> or = 90 mmHg) natriuresis (100 mmol/24 h in mean) between these different classes. The basal AR, the max AR, the DIF and the RC significantly differed between the 4 classes. They were greater in class III and IV than in class I. The positive criteria for the captopril test were max AR, DIF and RC. The positivity thresholds were max AR > or = 70 ng/l, DIF > or = 50 ng/l and RC > or = 165% (upper limit in the class I 95% confidence interval for each criterion).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin converting enzyme variability in hypertensive and normotensive rats

Recent data have revealed biological and genetic variability in normotensive Wistar-Kyoto rats, which are considered to be the most appropriate control strain for spontaneously hypertensive rats. To investigate the possibility that angiotensin converting enzyme activity could be affected by this variability, we measured plasma and tissue (lung, heart, renal cortex, renal medulla, and adrenal gland) angiotensin converting enzyme activity in spontaneously hypertensive rats and normotensive Wistar-Kyoto rats from three commercial suppliers in France: Iffa-Credo, Janvier, and Charles River Laboratories. Angiotensin converting enzyme activity was measured in vitro with a fluorometric assay using carbobenzoxy-Phe-His-Leu as substrate. Angiotensin converting enzyme activity in both rat strains varied considerably from one supplier to another, and therefore, comparisons of spontaneously hypertensive rats and Wistar-Kyoto rats from the different suppliers produced conflicting results. For Wistar-Kyoto rats, angiotensin converting enzyme activity in the plasma, heart, kidney, and adrenal glands was highest in rats from Iffa-Credo and lowest in rats from Charles River. For spontaneously hypertensive rats, angiotensin converting enzyme activity in the plasma and tissues was highest in rats from Janvier, whereas no difference could be observed between rats from Iffa-Credo and Charles River. These data confirm the problem of how to interpret and compare studies that use spontaneously hypertensive and Wistar-Kyoto rat strains.

Renal dopamine excretion in healthy volunteers after oral ingestion of L-dopa

L-Dopa is converted to dopamine by aromatic-L-amino acid decarboxylase (AADC). In the kidney, proximal tubular epithelial cells are rich in AADC and urinary free dopamine excretion is a marker for endorenal extraneuronal dopamine synthesis. The urinary free dopamine excretion was analysed in a double-blind cross-over study after oral ingestion of L-Dopa or a placebo in five healthy volunteers. The drug ingestions were separated by one week's wash-out. Since in a preliminary study, two volunteers ingesting a single L-Dopa dose of 500 mg with breakfast experienced nausea, the five volunteers of the present study were given 300 mg L-Dopa (50 mg at 9 am with breakfast, 100 mg before lunch and 150 mg before dinner) without any adverse effects. L-Dopa induced an increase in 24-h urinary dopamine excretion (HPLC with electrochemical detection). Free urinary dopamine (1900 micrograms/24 h) accounted for 0.8% of the daily oral L-Dopa dose and represented 10% of total urinary dopamine excretion. L-Dopa treatment had no significant effect on mean ambulatory arterial blood pressure and heart rate measured from 9 am to 6 pm (Spacelabs) or on 24 h urinary water and sodium excretion.

In vitro stability of the inhibition of serum converting enzyme by fosinopril

With captopril, it has been shown that an erroneous measurement of serum angiotensin converting enzyme (ACE) can be induced by the dissociation of the inhibitor-ACE complex during long-term storage. We have studied the possible dissociation of the fosinopril-ACE complex during the storage of serum samples from healthy male volunteers given a single dose of fosinopril. Serum samples were collected from 5 volunteers, 5 min before, then 4 and 24 h after a unique oral dose of 10 mg fosinopril. ACE activity was measured by a colorimetric and a fluorimetric assay during the hour following the sampling (day 0) and after 21 or 61 days of storage at -20 or -196 degrees C. The degree of ACE inhibition measured in vitro in fresh serum samples differed according to the technique used. Fosinopril has a long-lasting effect with 80% inhibition 24 hours after drug administration. Storage at -20 and -196 degrees C induced a significant decrease in the degree of inhibition measured with the colorimetric method. With the fluorimetric method, a decrease in ACE inhibition was only observed after storage at -20 degrees C but not at -196 degrees C.

The effects of muzolimine and urine from muzolimine-treated rats on Na+K+Cl- cotransport in Madin-Darby canine kidney cells

Muzolimine is a loop diuretic with an original chemical structure devoid of the acidic or sulfonamide group known to be necessary for an interaction with Na+K+Cl- cotransport. We studied the effects of urine from muzolimine-treated rats on the Na+K+Cl- cotransport-dependent 86Rb influx in MDCK cells. Na+K+Cl- cotransport was inhibited by urine obtained 15 min (42% inhibition) and 60 min (49% inhibition) after muzolimine injection (50 mumol/kg i.v.). Muzolimine itself was not detectable in the urine. Probenecid (100 mumol/kg i.v.) suppressed both the diuretic effect of muzolimine and the inhibition of Na+K+Cl- cotransport by urine from muzolimine-treated rats. These results suggest that the diuretic effect of muzolimine is due to the metabolism of muzolimine into an active compound which inhibits Na+K+Cl- cotransport after its secretion into the tubular lumen via a proximal pathway. The direct effect of muzolimine on Na+K+Cl- cotransport in MDCK cells was also tested: surprisingly, the inhibition of 86Rb influx was significant in the presence of muzolimine (IC50 = 1.44 microM). We show that this effect was due to the metabolism of muzolimine by these cells into an active compound.

Effects of dopamine prodrugs and fenoldopam on glomerular hyperfiltration in streptozotocin-induced diabetes in rats

The effects of dopamine (DA) prodrugs (L-dopa and gludopa) and of a D1-selective agonist (fenoldopam) on glomerular hyperfiltration were studied in the early stage of diabetes in rats. Wistar rats received one injection of streptozotocin (STZ) and were treated 1 week later with L-dopa (2 x 10 mg/kg/day, s.c.), gludopa (2 x 3 or 2 x 10 mg/kg/day, s.c.), or fenoldopam (2 x 0.3 or 2 x 1 mg/kg/day, s.c.). Their renal functions were compared with those of untreated diabetic and nondiabetic control rats. STZ injection led to hyperglycemia that was kept moderate (20-25 mmol/L) by daily insulin therapy (2-4 U of NPH insulin). Within 2 weeks, glomerular hyperfiltration (polyfructosan clearance) developed in diabetic rats (30% increase vs. nondiabetic control). A rise in renal plasma flow (PAH clearance) was sometimes observed. One week of treatment with either L-dopa, gludopa, or fenoldopam normalized the glomerular filtration rate and decreased filtration fraction. These corrections occurred despite similar metabolic disturbance and kidney hypertrophy. Gludopa was less well tolerated by diabetic rats than L-dopa. Results with L-dopa showed that the normalization of glomerular hyperfiltration was linked to DA synthesis and stimulation of D1 receptors, since it was reversed by carbidopa, a dopa decarboxylase inhibitor, and by SCH 23390, a D1-selective antagonist. These data show that DA prodrugs and a D1 agonist can suppress diabetic glomerular hyperfiltration in the very early course of the disease in rats.

[Changing factors of the activity of angiotensin converting enzyme of renal brush border in rats]

In the kidney, angiotensin I-converting enzyme (ACE) is present in the vascular endothelial cells and in the brush border of epithelial cells of the proximal tubule. In spite of this well-known distribution of ACE, little is known of its regulation. In order to elucidate the possible mechanisms of control for brush border ACE, the effects of dexamethasone (DM), (40 micrograms s.c. per day, for 7 days) and triiodothyronine (T3) 0.5 mg/kg s.c. per day, for 10 days) were investigated in male Wistar rats. Plasma and brush border ACE activities were measured by fluorimetry in the presence of an artificial substrate Cbz-Phe-His-Leu and brush border ACE was characterized with a binding assay using 3H-ramiprilat, a specific radiolabelled ACE inhibitor. DM elicited a significant decrease in plasma ACE activity (from 0.46 +/- 0.03 to 0.28 +/- 0.02 nmol His-Leu/min/mg protein) but did not alter enzyme activity in the brush border: 47.12 +/- 5.12 nmol His-Leu/min/mg protein (control, n = 6) and 47.78 +/- 5.63 (DM, n = 6). Administering T3 produced a marked increase in the brush border ACE activity (from 42.87 +/- 4.9 to 81.41 +/- 11.7 nmol His-Leu/min/mg protein). Similarly, the maximum number of 3H-ramiprilat-binding sites increased in the brush border, indicating a good correlation between ACE activity and the quantity of 3H-ramiprilat bound. Thus, the variation in tissue ACE activity corresponded to a change in the enzyme concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

[Do renal vascular D2 receptors exist?]

Two dopamine receptors are present on the renal vasculature: post-synaptic D1-receptors and neuronal D2-receptors. The existence of postsynaptic vascular D2-receptors is now under discussion. The aim of this study was to characterize in vitro the renal vascular response to bromocriptine, a D2 preferential agonist. Bromocriptine (10(-7) to 3.10(-5) M) induced a concentration dependent relaxation (EC50 = 1.4 +/- 0.1 x 10(-6) M, m +/- SEM, n = 5) on the isolated perfused rat kidney whose vascular tone had been previously increased by 25% with prostaglandin F2 alpha and adrenoceptors blocked (phenoxybenzamine 10(-5) M, sotalol 10(-5) M). Response to bromocriptine was comparable to that induced by dopamine on terms of EC50 and Emax (87 +/- 3% reversion of the increase in renal vascular resistance induced by prostaglandin F2 alpha). Nevertheless, unlike response to dopamine, bromocriptine-induced relaxation was not antagonized by the selective D1-receptor antagonist, SCH 23390 (3 x 10(-9) M) but was inhibited by selective D2-receptor antagonists, domperidone (10(-8) M) and DO 710 (3 x 10(-8) M). To account for renal vasodilatation, an interaction of bromocriptine with 5-HT receptors was excluded. Indeed, neither 8-OHDPAT, 5-methoxytryptamine nor 5-HT were able to induce any renal vasodilatation on the isolated perfused rat kidney and domperidone is devoid of antagonist activity on 5-HT receptors. The present results suggest that bromocriptine-induced vasodilatation on the rat renal vascular bed was linked to an interaction with vascular postsynaptic D2-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)