Angiotensin AT1 receptor antagonist irbesartan decreases lesion size, chemokine expression, and macrophage accumulation in apolipoprotein E-deficient mice.

Recent data suggest that angiotensin II AT1 receptor antagonists may be beneficial in the treatment of atherosclerosis. To clarify how AT1 receptor antagonists reduce atherosclerosis, the effect of irbesartan on atherosclerotic lesion development was determined in low-fat, chow-fed apolipoprotein (Apo) E-deficient mice. Irbesartan (50 mg/kg per day) strongly decreased lesion development after a 12-week treatment period (lesion size: irbesartan treated, 20,524 +/- 4,200 microm(2) vs. control, 99,600 +/- 14,500; 79.4% inhibition, p < 0.001). This effect was not due to an effect of irbesartan on lipoprotein levels because irbesartan slightly increased total cholesterol levels and decreased the ratio of Apo A-I relative to Apo B levels. Immunochemical analysis of the atherosclerotic lesions using the mac3 monoclonal antibody showed the presence of macrophages in the lesions of control mice, whereas sections from irbesartan-treated animals only showed occasional labeling in the lesion area. These data suggest that irbesartan inhibits monocyte/macrophage influx into the vessel wall. Therefore, expression levels of monocyte chemoattractant protein-1 (MCP-1), as well as other chemokines involved in macrophage infiltration into the lesion area, were measured in the aortic sinus of control and irbesartan-treated animals. Irbesartan treatment strongly decreased MCP-1 mRNA levels as well as MCP-1 immunostaining in the lesion area. This effect of irbesartan on MCP-1 occurred without an effect on CCR2, the receptor of MCP-1. Expression of macrophage inflammatory protein (MIP)-1alpha, another CC chemokine expressed in atherosclerotic lesions, was also reduced after irbesartan treatment, without effect on CCR3 and CCR5, the receptors of MIP-1alpha. Concomitantly, the expression of the angiogenic chemokines KC and MIP-2, which are functionally related to interleukin-8, were downregulated, whereas their shared receptor CXCR2 was upregulated. These data suggest that inhibition of the inflammatory component of lesion progression plays an important role in the inhibitory effect of AT1 receptor antagonists on atherosclerotic lesion formation.

Selective vasopressin, angiotensin II, or dual receptor blockade with developing congestive heart failure.

With developing congestive heart failure (CHF), activation of the vasopressin V(1a) and angiotensin II type 1 (AT(1)) receptors can occur. In the present study, we examined the direct effects of V(1a) receptor blockade (V(1a) block), selective AT(1) receptor blockade (AT(1) block), and dual V(1a)/AT(1) receptor blockade (dual block) with respect to left ventricular (LV) function and contractility during the progression of CHF. LV and myocyte functions were examined in pigs with pacing CHF (rapid pacing, 240 beats/min, 3 weeks, n = 10), pacing CHF with concomitant V(1a) block (SR49059, 60 mg/kg, n = 8), pacing CHF with concomitant AT(1) block (irbesartan, 30 mg/kg, n = 7), or pacing CHF with dual block (n = 7). LV end-diastolic dimension and peak wall stress were reduced in all receptor blockade groups compared with CHF values. However, LV fractional shortening was increased only in the dual block group compared with CHF values (29 +/- 3 versus 21 +/- 2, P <.05). Basal LV myocyte percent shortening increased in the dual block group compared with CHF values (3.44 +/- 0.23 versus 2.88 +/- 0.11, P <. 05). Although V(1a) or AT(1) block reduced LV loading conditions, only dual block resulted in improved LV and myocyte shortening.

Aquaretic and hormonal effects of a vasopressin V(2) receptor antagonist after acute and long-term treatment in rats.

A single oral administration of 1-[4-(N-tert-butylcarbamoyl)-2-methoxybenzene sulfonyl]-5-ethoxy-3-spiro-[4-(2-morpholinoethoxy)cyclohexane]indo l-2 -one SR121463 (0.3-3 mg/kg), a vasopressin non-peptide V(2) receptor antagonist, to rats induced dose-dependent aquaresis which was accompanied by Na(+), K(+), aldosterone and arginine vasopressin excretion over 6 h after dosing. However, no solute excretion was observed over 24 h. As a result of aquaresis, hemoconcentration and increases in plasma angiotensin II and adenocorticotrophin hormone were seen with 3 mg/kg at 2 h after dosing. Chronic treatment with SR121463 (3 mg/kg/dayx28 days) induced a marked aquaresis associated with aldosterone and vasopressin excretion. After a week of treatment, urine volume and aldosterone excretion were reduced ( approximately 40%) and then stabilised, while urine vasopressin excretion remained almost constant throughout the study. There were no changes in arterial pressure, plasma osmolality, plasma sodium concentration, or in number and affinity of liver vasopressin V(1A) and kidney V(2) receptors 24 h after the last treatment. These results indicate that SR121463 is a potent aquaretic agent and might be useful for the chronic management of water-retaining diseases in humans.

Nitric oxide, but not vasopressin V2 receptor-mediated vasodilation, modulates vasopressin-induced renal vasoconstriction in rats.

The renal vascular response to vasopressin and its modulation were evaluated in vivo by infusing the peptide directly into the renal artery of anaesthetized rats. The intra-renal artery (i.r.a) infusion of vasopressin induced a dose-dependent decrease in renal blood flow. Vasoconstriction was obvious at a dose of 3 ng/kg per min and reached a maximum at 100 ng/kg per min. The dose required for a half-maximal response (ED50) was 24+/-4 ng/kg per min (mean+/-SEM, n=8), corresponding to an estimated concentration in renal arterial blood required for a half-maximal response (EC50) of 1.9+/-0.6 nM. Thiobutabarbitone anaesthesia markedly increased plasma vasopressin concentration. This increase was prevented partially by hypotonic hydration of the rats without any change in the renal vascular response to exogenous vasopressin. Vasopressin-induced vasoconstriction dose/response curves were similar in homozygous and heterozygous Brattleboro rats. Infusion of desmopressin (1-1000 ng/kg per min, i.r.a.), a vasopressin V2 receptor-selective agonist, failed to induce renal vasodilation or vasoconstriction. In the presence of SR 49059 (1 mg/kg i.v.), a vasopressin V1A receptor antagonist that completely abolished the vasopressin-induced renal vasoconstriction, desmopressin again failed to induce vasodilation. Inhibition of nitric oxide synthase by N(omega)-nitro-L-arginine (L-NNA, 100 microg/kg for 10 min and 7.5 microg/kg per min, i.r.a.) enhanced vasopressin-induced renal vasoconstriction (EC50 0.6+/-0.1 nM, P<0.05). In contrast, cyclooxygenase blockade by indomethacin (5 mg/kg, i.v.) neither modified the vasopressin-induced decrease in renal blood flow nor altered the potentiation of vasoconstriction by L-NNA. These results show that the constrictor response of the rat renal vascular bed in vivo is observed only with high local concentrations of vasopressin. This hyporeactivity in vivo was not explained by an anaesthesia-elicited increase in endogenous vasopressin, nor by a modulatory effect linked to V2 receptor activation or prostanoid release. In contrast, NO release contributed to the attenuation of vasopressin-induced renal vasoconstriction.

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.

Effects of long-term angiotensin II AT1 receptor blockade on survival, hemodynamics and cardiac remodeling in chronic heart failure in rats.

OBJECTIVE: The beneficial effect of chronic angiotensin I converting enzyme (ACE) inhibition on survival has for long been established in the rat post-infarction model of chronic heart failure (CHF) and has subsequently been confirmed in humans. This study investigates in rats whether chronic angiotensin II AT1 receptor blockade shares with ACE inhibition the same beneficial effect. METHODS: Rats we subjected to coronary artery ligation and, from 7 days later, orally treated for 7.5 months with placebo or irbesartan (5 or 50 mg/kg/day). RESULTS: Irbesartan dose-dependently increased survival (placebo: 27%, low dose: 52%, high dose: 82%, sham-ligated: 100%; high dose vs placebo: P < 0.001 and vs low dose: P < 0.05; low dose vs placebo: P = 0.11). Irbesartan also dose-dependently decreased urinary cyclic GMP excretion throughout the study. At 7.5 months, it dose-dependently decreased left ventricular (LV) end diastolic pressure. normalized LV pressure maximal rate of rise (dP/dt) and cardiac index values and improved LV and right ventricular regional blood flows (radioactive microspheres) and resistances. At 7.5 months, irbesartan markedly decreased myocardial hypertrophy but had almost no effect on LV dilatation and subendocardial fibrosis. CONCLUSIONS: Long-term angiotensin II AT1 receptor blockade with irbesartan strongly and dose-dependently increases survival in the rat model of coronary ligation-induced CHF. This effect is due to the combination of the beneficial effects that the drug exerts on systemic and coronary hemodynamics, on cardiac pump function and vs cardiac hypertrophy development. Long-term AT1 receptor blockade might thus prove useful and prolong survival in human CHF.

Evaluation of the ability of irbesartan to cross the blood-brain barrier following acute intragastric treatment.

The present study evaluated in functional tests the ability of the angiotensin AT1 receptor antagonist irbesartan, 2-n-butyl-3-[(2'-(1H-tetrazol-5-yl)-biphenyl-4-yl)methyl]-1,3-d iaza-spiro[4,4]non-1-en-4-one, in comparison to losartan, 2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'(1H-tetrazol-5-yl) bi-phenyl-4-yl)methyl]imidazole, to cross the blood-brain barrier following acute intragastric administration. Two tests were used: the dipsogenic response to intracerebroventricular injection of angiotensin II, and Na+ intake in response to adrenalectomy. In normotensive rats, irbesartan reduced the dipsogenic response to angiotensin II, 10 pmol per rat, at the dose of 90 mg/kg, but not at lower doses. Losartan significantly reduced angiotensin II-induced drinking at 30 mg/kg, but not at a lower dose. In spontaneously hypertensive rats, irbesartan reduced the response to angiotensin II at 50 mg/kg, but not at lower doses, while losartan significantly inhibited angiotensin II-induced drinking even at 10 mg/kg. In adrenalectomized rats, the intake of 2% NaCl was inhibited by the intragastric administration of losartan 30 or 50 mg/kg, while irbesartan did not reduce it in doses up to 50 mg/kg. The results of the present study consistently indicate that after acute intragastric administration, the ability of irbesartan to cross the blood-brain barrier is lower than that of losartan.

Effects of irbesartan (SR47436/BMS-186295) on angiotensin II-induced pressor responses in the pithed rat: potential mechanisms of action.

The effects of two new non-peptide angiotensin receptor antagonists, irbesartan (SR 47436/BMS-186295, (2-n-butyl-4-spirocyclopentane-1-[((2'-tetrazol-5-yl)bipheny l-4-yl)methyl]2 - imidazolin-5-one) and SR 47155A (2-n-butyl-4-spirocyclopentane-1-[((2'-carboxy)biphenyl-4-yl)methy l]2- imidazolin-5-one, trifluoroacetate), on angiotensin II-induced pressor responses were studied in the pithed rat in comparison to losartan, EXP 3174 and [Sar1,Val5,Ala8]angiotensin II. SR 47155A (1-10 mg/kg i.v.) and losartan (1-10 mg/kg i.v.) shifted dose dependently the dose-response curve of angiotensin II to the right without affecting the maximal response. SR 47436 (0.3-10 mg/kg i.v.), EXP 3174 (0.03-1 mg/kg i.v.) and [Sar1,Val5,Ala8]angiotensin II (0.03-1 mg/kg i.v.) induced, at least at high doses, a non-parallel shift to the right of the angiotensin II dose-response curve and this was associated with a reduction of the maximal response. During a 70 min period, the effect of [Sar1,Val5,Ala8]angiotensin II (1 mg/kg i.v.) on the angiotensin II (0.3 microgram/kg i.v.)-induced pressor response was shown to be reversible, the effect of SR 47155A (10 mg/kg i.v.) was partially reversible and the effect of SR 47436 (3 mg/kg i.v.), EXP 3174 (1 mg/kg i.v.) or losartan (6 mg/kg i.v.) was not reversed at the end of this 70 min period. Administration of SR 47155A (10 mg/kg i.v.) before SR 47436 (1-10 mg/kg i.v.) reversed the reduced angiotensin II-maximal response induced by SR 47436. Administration of SR 47436 (10 mg/kg i.v.) before SR 47155A (1-10 mg/kg i.v.) prevented the full development of the pressor response as observed in the absence of SR 47436. In the pithed rat, SR 47436 (30 mg/kg i.v.) and losartan (30 mg/kg i.v.) reduced the change in diastolic blood pressure induced by electrical stimulation of the spinal cord only at low stimulation rates. Taken together these results indicate that SR 47436, under in vivo conditions, is a potent non-peptide angiotensin receptor antagonist. The type of antagonism (partially insurmountable but selective) can be explained by different theoretical models which are discussed.

Are vasopressin peripheral V1 receptors involved in the development of malignant hypertension and stroke in SHR-SPs?

The aim of this study was to determine whether activation of vasopressin (AVP) peripheral V1 receptors is involved in the development of malignant hypertension, stroke, and end-organ damage in stroke-prone spontaneously hypertensive rats (SHR-SPs). For this purpose, young salt-loaded SHR-SPs were treated orally daily from their 5th to 34th week of age, by a selective AVP V1 receptor antagonist, SR 49059, used in a dose (30 mg/kg) that achieved complete peripheral V1 receptor blockade. Untreated SHR-SPs served as controls. SR 49059 slightly and transiently (8th to 10th week of age) limited the rise in blood pressure, but thereafter systolic blood pressure values were similar in the two groups of SHR-SPs. Stroke-related mortality was not significantly different in SR 49059-treated and in control animals (65% vs 65% at 30 weeks, 65% vs 83% at 34 weeks). SR 49059 did not prevent the increases in fluid intake, diuresis and proteinuria seen in controls. Histological examination of the brain, kidneys and heart revealed that the development of fibrinoid necrosis and arterial thickening was not prevented by SR 49059, nor was that of malignant nephroangiosclerosis and of myocardial infarction and fibrosis. These data strongly suggest that AVP peripheral V1 receptor activation is not involved in the pathological processes that develop in SHR-SPs.

Efficacy of SR 47436 (BMS-186295), a non-peptide angiotensin AT1 receptor antagonist in hypertensive rat models.

The efficacy of SR 47436 (BMS-186295), 2-n-butyl-3-[(2'-(1H-tetrazol-5-yl)- biphenyl-4-yl)methyl]-1,3-diaza-spiro[4,4]non-1-en-4-one, a non-peptide angiotensin AT1 receptor antagonist, was characterized in various conscious hypertensive rat models. In spontaneously hypertensive rats, single intravenous or oral doses of SR 47436 induced mild to modest antihypertensive effects. No tolerance of the antihypertensive effect was observed when the oral treatment was extended to 15 days. SR 47436 was highly effective to lower blood pressure in high renin-dependent hypertensive models such as two-kidney, one-clip renal hypertensive rats and renal artery-ligated hypertensive rats. In this last model, intravenous or oral administration of the angiotensin II antagonist produced a dose-dependent decrease in blood pressure. When injected after the maximal effective dose, enalapril did not induce any further decrease in blood pressure. Furthermore, the antihypertensive effect elicited after a single oral dose (10 mg/kg) was long-lasting (at least 24 h). The simultaneous blunting effect of the angiotensin II-induced blood pressure increase indicated clearly that the antihypertensive effect was due to the blockade of vascular angiotensin AT1 receptors. As expected, the angiotensin AT1 receptor antagonist did not show any efficacy in deoxycorticosterone acetate hypertensive rats, with a suppressed renin-angiotensin system. In genetic and renal hypertensive rats, the antihypertensive effect induced after acute dosing of SR 47436 was similar to that observed after losartan and enalapril. A reflex tachycardia accompanied the antihypertensive effect only after intravenous treatment with either SR 47436 or losartan. These results show that this angiotensin II antagonist, SR 47436, is an effective and long-lasting antihypertensive agent in rats.

A pharmacodynamic study of SR 47436, a selective AT1 receptor antagonist, on blood pressure in conscious cynomolgus monkeys.

1. Conscious normotensive cynomolgus monkeys were chronically instrumented for the measurement of arterial blood pressure and heart rate to investigate the relationships between the plasma concentration, suppression of the pressor response to angiotensin II (AII), compensatory increase in plasma AII, and hypotensive effect obtained after a single oral dose of SR 47436, a potent and specific nonpeptide AT1 receptor antagonist. As blood sampling could influence the hypotensive effect of SR 47436 through activation of the renin angiotensin system (RAS), drug effects were studied in groups of animals with or without blood samplings. 2. SR 47436 at 10 mg kg-1 induced a hypotensive effect which was not greater following a second dose of 30 mg kg-1, indicating that a maximal hypotensive effect had already been obtained. 3. A single oral dose of SR 47436 (10 mg kg-1) caused a sustained hypotension and a marked inhibition of the AII-induced pressor response, lasting for up to 28 h. These effects of SR 47436 are consistent with good oral bioavailability and a slow elimination of the drug (t 1/2 approximately 20 h), and were accompanied by a sustained increase in plasma AII concentration. Taken together, both the hypotensive response and the compensatory increase in AII indicated that vascular and juxtaglomerular AII receptors were blocked. 4. Although a fair correlation between individual plasma drug concentrations and inhibition of AII-induced pressor response was observed, neither the hypotensive effect nor the compensatory increase in AII correlated with the plasma drug levels. 5. Basal arterial pressure and AII-induced pressor response were not affected by blood samplings. 6. These results suggest that SR 47436 is an effective and long lasting AT1 receptor antagonist with a potent hypotensive action in normotensive cynomolgus monkeys. It may be an efficacious blocker of the RAS in man and suitable for once-a-day dosing.

Effect of SR 47436, a novel angiotensin II AT1 receptor antagonist, on human vascular smooth muscle cells in vitro.

Proliferation of smooth muscle cells within the intima plays a key role in vascular occlusive disorders such as atherosclerosis and restenosis following balloon angioplasty. Among the factors that may be important in the development of vascular lesions, several authors have reported that the local angiotensin system participates in modulating the proliferation of smooth muscle cells after arterial injury. This study was therefore designed to characterize the antagonistic properties and to investigate the antiproliferative effect of a newly developed non-peptide angiotensin II AT1 receptor antagonist, SR 47436. This compound is a potent and competitive antagonist of the binding of [125I]angiotensin II to its receptor on cultured human aortic smooth muscle cells, exhibiting an IC50 value of 1.7 +/- 0.6 nM. SR 47436 was 10-fold more potent than DuP 753 (Losartan) (IC50 = 20.8 +/- 3.7 nM). In these same cells, SR 47436 potently inhibited the angiotensin II-induced [Ca2+]i increase (IC50 = 0.53 +/- 0.13 vs. 7.4 +/- 1.3 nM for DuP 753). Angiotensin II is a potent mitogen for human aortic smooth muscle cells in culture, exhibiting a maximum proliferative response at 1 microM. SR 47436 and Losartan prevented angiotensin II-induced proliferation of these cells in a dose-dependent manner (IC50 = 0.32 +/- 0.09 and 0.71 +/- 0.08 microM, respectively). SR 47436 displayed a marked in vitro inhibition of serum-induced smooth muscle cell proliferation (IC50 = 5.5 +/- 0.8 microM). A selective AT2 receptor antagonist, PD 123177 did not affect angiotensin II-induced responses in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological study of SR 47436, a non-peptide angiotensin II AT1-receptor antagonist, in conscious monkeys.

OBJECTIVE: The hypotensive and hormonal responses of an AT1-subtype angiotensin II receptor antagonist, SR 47436, were investigated and compared with those of DuP 753 (losartan), the leading AT1-receptor antagonist, and captopril and enalapril, two major angiotensin converting enzyme (ACE) inhibitors, in conscious, sodium-replete and sodium-depleted non-human primates. DESIGN AND METHODS: Blood pressure and heart rate were measured in conscious, chronically instrumented sodium-replete (n = 3-5) and sodium-depleted (n = 4) cynomolgus monkeys (Macaca fascicularis). Plasma renin activity (PRA), active renin and angiotensin II plasma concentrations were determined. RESULTS: SR 47436 induced a dose- and time-related fall in blood pressure in sodium-depleted monkeys; the blood pressure-lowering effect was obtained at a range of doses from one-third to one-tenth the equihypotensive dose of DuP 753 after intravenous and oral administrations. The hypotensive effect obtained with SR 47436 was similar to that of captopril and was sustained in sodium-replete monkeys, although it was weaker and less long-lasting than that of enalaprilat. In both sodium-depleted and sodium-replete monkeys the AT1 antagonist and ACE inhibitors caused similar increases in PRA and active renin. However, although angiotensin II levels increased after SR 47436 or DuP 753 treatment, they decreased after treatment with enalaprilat. Modest decreases in the heart rate sometimes accompanied the hypotension, irrespective of the compound tested. CONCLUSION: These data demonstrate that the AT1 antagonist SR 47436 is an effective hypotensive agent in both sodium-replete and sodium-depleted monkeys, with an intrinsic potency three to 10 times that of DuP 753 and similar to that of ACE inhibitors.

Characterization of cardiac angiotensin AT1 receptors by [3H]SR 47436.

[3H]SR 47436, a selective and potent novel non-peptide antagonist of angiotensin receptors, was used to characterize the cardiac angiotensin AT1 receptors. In neonatal rat heart cells, Scatchard analysis showed a single class of high affinity binding sites (Kd = 0.24 nM, Bmax = 28 fmol/mg protein). The binding was saturable, reversible and prevented by angiotensin II and the AT1 subtype receptor antagonist DuP 753 whilst unaffected by the AT2 receptor antagonist PD123177. In the same cells, angiotensin II induced a twofold increase in the intracellular free Ca2+ concentration ([Ca2+]i), with a half-maximal effect (EC50) at 14 nM. This increase was prevented by SR 47436 (IC50 = 1.03 nM) and by the AT1 receptor antagonist DuP 753, but at higher concentrations (IC50 = 15.6 nM) and was unaffected by PD123177. These data directly demonstrate the presence of cardiac AT1 receptors in rat neonatal cardiomyocytes and confirm the involvement of AT1 receptors in cardiac Ca2+ homeostasis.

Pharmacological characterization of SR 47436, a new nonpeptide AT1 subtype angiotensin II receptor antagonist.

SR 47436, 2-n-butyl-3-[(2'-(1H-tetrazol-5-yl)-biphenyl-4-yl) methyl]-1,3-diaza-spiro[4,4]non-1-en-4-one, is a new potent and selective AT1 angiotensin II (AII) receptor antagonist. It competitively inhibited [125I]AII binding to AT1 subtype receptors in rat liver membranes (IC50 = 1.7 nM) and did not interact with AT2 subtypes in rat adrenal cortical membranes. In rabbit aorta, SR 47436 inhibited contractions induced by 10 nM AII (IC50 = 4.0 nM) and shifted AII contractile response curves to the right in a parallel fashion, without total recovery of the maximal response. The potency of SR 47436 was higher than that of the lead compound, 2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'-(1H-tetrazol-5- yl)biphenyl-4-yl)methyl]imidazole (DuP 753) (rat liver binding: IC50 = 16 nM; rabbit aorta: IC50 = 26 nM), and equivalent to saralasin (IC50 = 1.8 and 2.7 nM, respectively). The high specificity of SR 47436 was demonstrated by its lack of activity (IC50 > 10 microM) on various other receptors, ionic channels and antiports and rabbit aorta contracted by norepinephrine and KCl, and its lack of inhibition of renin and converting enzyme. In conscious rats, SR 47436 as well as DuP 753 (0.1 to 3 mg/kg, i.v., and 0.3 to 30 mg/kg, p.o.) antagonized the AII-pressor response in a dose-related manner. In conscious dogs, SR 47436 (1-10 mg/kg, p.o.) was a more potent antagonist of the AII pressor response than DuP 753. In conscious chronically implanted cynomolgus monkeys, SR 47436 antagonized the AII-pressor response at 1 mg/kg (89% i.v. and 66% p.o.) much more strongly than DuP 753 at 10 mg/kg (83% i.v. and 20% p.o.).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of a pseudo-tetrapeptide as renin inhibitor on blood pressure and renin-angiotensin system of sodium-repleted and sodium-depleted hypertensive patients.

The blood pressure and renin-angiotensin system effects of the new renin inhibitor, SR 43845 ([N-(pyridyl-3-propionyl)-phenylalanyl- histidyl-(3S,4S) ACHPA-isoleucylamino]-2-methyl-2-dihydroxy-1,3-propane), were studied in 12 hypertensive patients on a normal sodium intake who received a 30-min infusion of intravenous SR 43845 at one of 3 doses: 30, 100 or 300 micrograms/kg (4 patients per group). Eight further patients were infused with the 300 micrograms/kg dose 24 h after 80 mg furosemide orally. In sodium-repleted patients, the 30, 100 and 300 micrograms/kg doses induced a rapid fall in diastolic blood pressure (DBP) which culminated at 4.5, 7.5 and 3.9 mmHg, respectively. Salt depletion increased the renin inhibitor-induced fall in DBP to 10.8 mmHg. DBP was back to baseline at 60 min after starting the lowest dose and 180 min after starting the highest dose. Heart rate did not change. In four of the sodium-depleted patients, 50 mg captopril was given orally at T = 180 min, when blood pressure had returned to baseline. The decrease in BP (8.8 mmHg) was similar to that initially obtained with the renin inhibitor (10.1 mmHg). Plasma angiotensin (Ang) I was dose-dependently reduced by 62, 93 and 92% of baseline values 10 min after the start of the infusion in sodium-repleted patients, and by 90% in sodium-depleted patients; it returned to baseline in both situations between 180 and 360 min. Plasma Ang II levels changed in parallel with those of plasma Ang I.(ABSTRACT TRUNCATED AT 250 WORDS)

[A new method for determination of renin inhibitors]. / Une nouvelle méthode de dosage des inhibiteurs de rénine.

To determine the concentration of renin inhibitors in plasma or other biological fluids, we developed an original approach to the already existing methods, such as HPLC or radio-inhibitor binding and enzyme inhibitor assays. We made an antigen-antibody complex by linking human renin (0.8 nM) to a specific monoclonal antibody fixed to magnetic spheres (3E8-magnogel). A binding technique with 3H-43845 (4 nM) was applied to this preparation to assess the association and dissociation kinetics of SR 43845, a highly potent and specific renin inhibitor. Standard curves were built and CI50 was 0.53 +/- 0.07 nM (n = 5). One of the application of this method is the biochemical characterization of renin inhibitors. We close several various chemical structure renin inhibitors having the inhibiting activity of 0.01 to 10,000 nM (CI50 human PRA). Preliminary results show a good correlation (r = 0.97; n = 12) with those obtained in plasma. In other respects, this new assay was applied to determine SR 43845 plasma concentrations in human pharmacokinetic studies and in primate pharmacological studies. The limit of detection was 0.09 ng/ml. Finally, it is now possible to perform a relationship between plasma concentrations of renin inhibitor and blood pressure changes or other biochemical parameters changes to allow a better understanding to the renin-angiotension system.

Effects of a renin inhibitor, SR 43845, and of captopril on blood pressure and plasma active renin in conscious sodium-replete macaca.

The effects of the renin inhibitor, SR 43845 (IC50 = 10(-11) mol/l human and primate plasma renin) and of the angiotensin converting enzyme (ACE) inhibitor captopril on blood pressure and plasma active renin were investigated in conscious, chronically instrumented, sodium-replete macaca (cynomolgus monkeys). Perfusion of SR 43845 at 0.33, 3.3, 33, 100 and 200 micrograms/kg per min for 30 min elicited a dose-related decrease in blood pressure with a notable effect on plasma renin activity (PRA; 90% inhibition), beginning at a dose of 0.33 micrograms/kg per min. The maximal reduction in blood pressure of 22 +/- 2 mmHg (from 110 +/- 5 mmHg) was achieved at 100 micrograms/kg per min and a higher dose (200 micrograms/kg per min) induced no further reduction. Plasma levels of active renin were also significantly increased (to 104%, from 102 +/- 14 pg/ml) at the lower dose. Captopril, tested at 33 micrograms/kg per min under the same experimental conditions, lowered blood pressure in a similar manner and with the same intensity as the renin inhibitor at an equal dose (by 14 +/- 1 mmHg, from 114 +/- 4 mmHg). However, a dose six times as high only influenced the decrease of blood pressure slightly (by 16 +/- 2 mmHg, from 103 +/- 5 mmHg). For the same hypotensive effect, the plasma renin concentration was significantly higher with the renin than with the ACE inhibitor. The recovery of pre-infusion blood pressure was both time- and dose-dependent, the basal value being almost restored after 5 h with both inhibitors, although the initial plasma renin levels were not completely recovered. A comparison of the maximal hypotensive effects and the plasma active renin concentrations elicited by the renin and the ACE inhibitors suggests that there are no major differences between the two types of inhibition and that renin inhibition is slightly more efficient.

[Increase in plasma levels of active and inactive renin after inhibition of renin activity by SR 42128 in conscious Macaca monkeys]. / Augmentation des taux plasmatiques de rénine active et inactive après inhibition de l'activité rénine par le SR 42128 chez le macaque vigile.

Plasma active renin (PAR), plasma inactive renin (PIR), and plasma renin activity (PRA) were determined after intravenous bolus injection of the renin inhibitor SR 42128, in sodium repleted and sodium depleted macacas. The kit renin of Pasteur Diagnostics allows determination of PAR after renin inhibition by SR 42128. PAR and total plasmatic renin (TPR) were determined before and after treatment of plasma using trypsin. IR = TPR-PAR. ARP was measured by RIA of angiotensin I. Sodium depletion induced a dramatic increase of PAR (1,678 + 11.5 pg/ml compared to 94.4 + 11.5, n = 6). PIR rose from 322.1 + 34.3 pg/ml to 1,137 + 206 (n = 6). In sodium repleted macacas, SR 42128 (3 mg/kg and 9 mg/kg) induced a PRA inhibition of 90 to 100 p. 100, for 4 h post-injection. PAR increased to reach maximal level after 90 min and remained constant up to 4 h post-injection (increase of 420 p. 100 at 3 mg/kg and 620 p. 100 at 9 mg/kg). PIR increased more slowly for 4 h (maximum increase of 250 p. 100). PRA was also inhibited in sodium depleted macacas by SR 42128 at the doses of 3 mg/kg and 9 mg/kg ARP was inhibited. PIR increased more slowly, but significantly at 9 mg/kg. We conclude that the activity of SR 42128 on PAR and PIR levels is the sole consequence of the inhibition of the Renin Angiotensin system.