Renal vascular reactivity to vasopressin in rats with diabetes mellitus.

We evaluated how renal vascular reactivity to vasopressin changes when nitric oxide (NO) synthesis varies, as has been reported to occur in the course of insulin-dependent diabetes mellitus. Renal vasoconstrictor responses to vasopressin were obtained in young and older Sprague-Dawley control rats (3 and 10 months old) and in age-matched diabetic rats that had been treated with streptozotocin (60 mg/kg i.v.) at the age of 2 months. In young rats, vasopressin (3-1000 ng/kg/min i.v.) induced in vivo a dose-dependent decrease in renal blood flow, which was diminished in streptozotocin diabetic rats (P<0.05). Similarly, in in vitro perfused kidneys, the concentration-response curve for vasopressin (0.03-10 nM) was shifted 3-fold to the right in kidneys isolated from young diabetic rats (P<0.05). This shift was abolished in the presence of an inhibitor of nitric oxide synthesis, N(G)-nitro-L-arginine (100 microM), in the perfusate. In 10-month-old rats, the in vivo renal vasoconstrictor dose-response curve to vasopressin was shifted 10-fold to the left as compared to that for young rats (P<0.001). This shift was similar in both control and diabetic rats. In conclusion, the present study documented the existence of hyporesponsiveness to vasopressin in the early stage of diabetes, possibly related to nitric oxide overproduction. In contrast, renal vascular hyperreactivity to vasopressin occurs with aging, whether the rats are diabetic or not.

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.

Electrophysiological effects of dronedarone (SR 33589), a noniodinated amiodarone derivative in the canine heart: comparison with amiodarone.

The electrophysiological effects of dronedarone, a new nonionidated analogue of amiodarone were studied after chronic and acute administration in dog Purkinje fibres, papillary muscle and isolated ventricular myocytes, and compared with those of amiodarone by applying conventional microelectrode and patch-clamp techniques. Chronic treatment with dronedarone (2x25 mg(-1) kg(-1) day p.o. for 4 weeks), unlike chronic administration of amiodarone (50 mg(-1) kg(-1) day p.o. for 4 weeks), did not lengthen significantly the QTc interval of the electrocardiogram or the action potential duration (APD) in papillary muscle. After chronic oral treatment with dronedarone a small, but significant use-dependent V(max) block was noticed, while after chronic amiodarone administration a strong use-dependent V(max) depression was observed. Acute superfusion of dronedarone (10 microM), similar to that of amiodarone (10 microM), moderately lengthened APD in papillary muscle (at 1 Hz from 239.6+/-5.3 to 248.6+/-5.3 ms, n=13, P<0.05), but shortened it in Purkinje fibres (at 1 Hz from 309.6+/-11.8 to 287.1+/-10.8 ms, n=7, P<0.05). Both dronedarone (10 microM) and amiodarone (10 microM) superfusion reduced the incidence of early and delayed afterdepolarizations evoked by 1 microM dofetilide and 0.2 microM strophantidine in Purkinje fibres. In patch-clamp experiments 10 microM dronedarone markedly reduced the L-type calcium current (76.5+/-0.7 %, n=6, P<0.05) and the rapid component of the delayed rectifier potassium current (97+/-1.2 %, n=5, P<0.05) in ventricular myocytes. It is concluded that after acute administration dronedarone exhibits effects on cardiac electrical activity similar to those of amiodarone, but it lacks the 'amiodarone like' chronic electrophysiological characteristics.

High concentrations of oxytocin cause vasoconstriction by activating vasopressin V1A receptors in the isolated perfused rat kidney.

The aim of this study was to evaluate the renal vascular effects of oxytocin in Sprague-Dawley rats and in Brattleboro heterozygous or homozygous rats, the latter being genetically deficient in vasopressin synthesis. Studies were performed in vitro, in the isolated kidney perfused in an open circuit with a Tyrode's solution. Oxytocin induced a concentration-dependent renal vasoconstriction in Sprague-Dawley rats, at rather high concentrations (EC50=170+/-39 nM, mean +/- SEM, n=6) with a maximum response amounting to 44% of that elicited by vasopressin (increase in renal vascular resistance: 11.5+/-0.9 mmHg min ml(-1) vs. 26.2+/-2.2 mmHg min ml(-1)). Oxytocin-evoked renal vasoconstriction was abolished by SR 49059, a selective vasopressin V1A receptor antagonist (10 nM), but not by d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr-(NH2)9] vasotocin, an oxytocin receptor antagonist (10 nM). In the presence of SR 49059, oxytocin did not induce renal vasorelaxation. Oxytocin induced renal vasoconstriction in Brattleboro homozygotes and heterozygotes (EC50=59+/-12 nM and 262+/-110 nM; Emax=7.8+/-1.1 mmHg min ml(-1) and 6.9+/-0.4 mmHg min ml(-1), n=5 respectively) with characteristics similar as observed in Sprague-Dawley rats concerning partial agonist activity, low potency and antagonism by SR 49059. Responsiveness to vasopressin did not differ in Brattleboro homozygotes and heterozygotes (EC50 approximately 0.25 nM) and was similar as we reported in Sprague-Dawley rats. These findings indicate that high concentrations of oxytocin induce renal vasoconstriction in the rat by activating vasopressin V1A receptors. The low agonist activity makes it unlikely that oxytocin can substitute functionally for vasopressin at the renal vascular V1A receptor in Brattleboro homozygous rats which are deficient in endogenous vasopressin.

Inhibitory effects of dronedarone on muscarinic K+ current in guinea pig atrial cells.

Dronedarone (SR33589), an amiodarone-like noniodinated antiarrhythmic agent, is undergoing clinical trials in atrial fibrillation. Because vagal activation plays a role in the pathophysiology of supraventricular arrhythmias, we have assessed the ability of dronedarone (0.01, 0.1, and 1 microM), compared with amiodarone (0.1, 1, and 10 microM) to inhibit the muscarinic acetylcholine receptor-operated K+ current (I(K(ACh))) in single cells isolated from guinea pig atria (patch-clamp technique). I(K(ACh)) was activated by extracellular application of carbachol (10 microM) or by intracellular loading with GTP-gamma-S (100 microM). Dronedarone and amiodarone reduced the carbachol-induced I(K(ACh)) with an IC50 (concentration required for 50% inhibition) slightly above 10 nM and 1 microM, respectively. Dronedarone also inhibited the GTP-gamma-S induced K+ current by 28% and 58% at 0.01 and 0.1 microM, respectively. These data suggest that dronedarone inhibits I(K(ACh)) by depressing the function of K(ACh) channel itself or associated GTP-binding proteins. Compared with amiodarone, dronedarone is approximately 100 times more potent on I(K(ACh)) and seems more selective in inhibiting I(K(ACh)) with respect to its antagonism of other inward and outward currents reported in the literature. This relative high potency of dronedarone to reduce I(K(ACh)) may be involved, at least in part, in the antiarrhythmic action of dronedarone against atrial fibrillation.

Effects of angiotensin II AT1-receptor blockade on coronary dynamics, function, and structure in postischemic heart failure in rats.

Angiotensin II AT1-receptor blockers (AT1-s) prolong survival in experimental postischemic (coronary artery ligation) heart failure (CHF) in rats. The goal of this study was to investigate whether potential beneficial effects of short- and/or long-term treatment with AT1-s on coronary dynamics, function, and structure develop along with the drug-induced survival prolongation in this model. Coronary blood flow was measured (fluorescent microspheres) in conscious sham, untreated, and irbesartan-treated (50 mg/kg daily for 6 weeks or 6 months, starting 8 days after surgery) CHF rats at baseline and at maximal vasodilatation induced by dipyridamole, and coronary dilatation reserve (CDR) was calculated as the ratio of maximal to baseline coronary flow. Coronary endothelial function was assessed in vitro by measuring the coronary relaxant responses to acetylcholine in the three groups of animals. Finally, cardiac hypertrophy and pericoronary fibrosis also were investigated. In CHF rats, left (LV) and right (RV) ventricular CDR were markedly depressed at both 7 weeks and 6 months after ligation, whereas coronary endothelial function was significantly impaired only after 6 months. Short-term AT1-receptor blockade with irbesartan did not prevent CDR deterioration at 7 weeks, nor did it significantly oppose cardiac hypertrophy and pericoronary fibrosis development. Prolonged AT1-receptor blockade prevented both RV CDR deterioration and coronary endothelial function impairment. It also limited significantly the increase in LV end diastolic pressure and the development of cardiac hypertrophy and pericoronary fibrosis. In conclusion, in postischemic CHF in rats, alterations of CDR precede those of coronary endothelial function. Long-, but not short-term AT1-receptor blockade prevents endothelial function degradation, opposes RV CDR impairment, prevents pericoronary fibrosis development, and improves systemic hemodynamics. These effects of AT1-s on coronary dynamics, function, and structure (i.e., on myocardial perfusion) may contribute to the drug-induced survival prolongation in this model.

Hemodynamic and antiadrenergic effects of dronedarone and amiodarone in animals with a healed myocardial infarction.

The hemodynamic and antiadrenergic effects of dronedarone, a noniodinated compound structurally related to amiodarone, were compared with those of amiodarone after prolonged oral administration, both at rest and during sympathetic stimulation in conscious dogs with a healed myocardial infarction. All dogs (n = 6) randomly received orally dronedarone (10 and 30 mg/kg), amiodarone (10 and 30 mg/kg), and placebo twice daily for 7 days, with a 3-week washout between consecutive treatments. Heart rate (HR), mean arterial pressure (MBP), positive rate of increase of left ventricular pressure (+LVdP/dt), echocardiographically assessed left ventricular ejection fraction (LVEF), and fractional shortening (FS), as well as chronotropic response to isoproterenol and exercise-induced sympathetic stimulation were evaluated under baseline and posttreatment conditions. Resting values of LVEF, FS, +LVdP/dt, and MBP remained unchanged whatever the drug and the dosing regimen, whereas resting HR was significantly and dose-dependently lowered after dronedarone and to a lesser extent after amiodarone. Both dronedarone and amiodarone significantly reduced the exercise-induced tachycardia and, at the highest dose, decreased the isoproterenol-induced tachycardia. Thus, dronedarone and amiodarone displayed a similar level of antiadrenergic effect and did not impair the resting left ventricular function. Consequently, dronedarone might be particularly suitable for the treatment and prevention of various clinical arrhythmias, without compromising the left ventricular function.

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.

Cellular and in vivo electrophysiological effects of dronedarone in normal and postmyocardial infarcted rats.

We studied the effects of dronedarone (SR 33589) on the action potentials, membrane ionic currents, and arrhythmic activity in control rats and in rats after myocardial infarction, a model known to develop anomalous electrical activity. Dronedarone increased action potential duration in normal hearts. It had little effect on the action potentials that were already prolonged in the postmyocardial infarcted (PMI) rats. Particularly, dronedarone reduced the late sustained K(+) current, I(K) (or Isus) by 69%. Dronedarone induced only a tonic block of I(K). Similar relative inhibitions of I(K) by dronedarone were obtained in young, sham, and PMI rats, even if I(K) was less in sham than in young and further reduced in PMI rats. The EC(50) values were 0.78 and 0.85 microM in sham and PMI rats. Dronedarone induced a weak increase in the fast transient outward current, I(to). Time-to-peak and inactivation time constant of I(to) were decreased by dronedarone that also induced a marked slowing of I(to) recovery from inactivation. Similar effects were observed on the reduced I(to) recorded in PMI rats. Holter monitoring study in control, unthetered animals showed that dronedarone had no proarrhythmic effect. On rats, which after myocardial infarction exhibited ventricular premature beats, dronedarone significantly decreased beat occurrence during the 7-day treatment; this effect was sustained for two more weeks. Thus, dronedarone exerts antiarrhythmic effects on PMI rat heart. Its effects are attributable for the most part to the inhibition of outward K(+) currents and the increase in effective refractory period.

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.

[Modulation by nitric oxide of vasopressin induced renal vasoconstriction varies with perfusate viscosity in the isolated rat kidney]. / La modulation par le monoxyde d'azote de la vasoconstriction rénale induite par la vasopressine varie avec la viscosité du perfusat sur le rein isolé perfusé de rat.

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.

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.

Characterization of SR 121463A, a highly potent and selective, orally active vasopressin V2 receptor antagonist.

SR 121463A, a potent and selective, orally active, nonpeptide vasopressin V2 receptor antagonist, has been characterized in several in vitro and in vivo models. This compound displayed highly competitive and selective affinity for V2 receptors in rat, bovine and human kidney (0.6 < or = Ki [nM] < or = 4.1). In this latter preparation, SR 121463A potently antagonized arginine vasopressin (AVP)-stimulated adenylyl cyclase activity (Ki = 0.26+/-0.04 nM) without any intrinsic agonistic effect. In autoradiographic experiments performed in rat kidney sections, SR 121463A displaced [3H]AVP labeling especially in the medullo-papillary region and confirmed that it is a suitable tool for mapping V2 receptors. In comparison, the nonpeptide V2 antagonist, OPC-31260, showed much lower affinity for animal and human renal V2 receptors and lower efficacy to inhibit vasopressin-stimulated adenylyl cyclase (Ki in the 10 nanomolar range). Moreover, OPC-31260 exhibited a poor V2 selectivity profile and can be considered as a V2/V1a ligand. In normally hydrated conscious rats, SR 121463A induced powerful aquaresis after intravenous (0.003-0.3 mg/kg) or oral (0.03-10 mg/kg) administration. The effect was dose-dependent and lasted about 6 hours at the dose of 3 mg/kg p.o. OPC-31260 had a similar aquaretic profile but with markedly lower oral efficacy. The action of SR 121463A was purely aquaretic with no changes in urine Na+ and K+ excretions unlike that of known diuretic agents such as furosemide or hydrochlorothiazide. In addition, no antidiuretic properties have been detected with SR 121463A in vasopressin-deficient Brattleboro rats. Thus, SR 121463A is the most potent and selective, orally active V2 antagonist yet described and could be a powerful tool for exploring V2 receptors and the therapeutical usefulness of V2 blocker aquaretic agents in water-retaining diseases.

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.

Study of SR 142801, a new potent non-peptide NK3 receptor antagonist on cardiovascular responses in conscious guinea-pig.

1. The cardiovascular responses to intravenous (i.v.) injection of natural tachykinins, substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and selective tachykinin (NK) receptor agonists, [Sar9, Met(O2)11]SP, [beta Ala8]NKA(4-10), [MePhe7]NKB and senktide were assessed in conscious, freely moving, guinea-pigs. 2. SP and [Sar9, Met(O2)11]SP (1-1000 pmol kg-1) induced dose-dependent decreases in mean arterial blood pressure (MAP) accompanied by increases in heart rate (HR). NKA evoked only weak hypotensive effects at high doses (3000 pmol kg-1) whereas [beta Ala8]NKA(4-10) (1-3000 pmol kg-1) had no effects. By contrast, NKB [MePhe7]NKB (1-10,000 pmol kg-1) and senktide (1-1000 pmol kg-1), produced dose-related hypertensive effects with the following rank order of potency: senktide > [MePhe7]NKB > NKB. Bradycardia occurred simultaneously with the increases in arterial pressure. 3. The pressor response to intravenous injection of senktide (300 pmol kg-1) was partially reduced by pretreatment with prazosin (0.71 mumol kg-1), or clonidine (0.38 mumol kg-1) and was completely inhibited by the combination of the two compounds. Atropine (1.5 mumol kg-1) suppressed the decrease in HR induced by senktide without altering the blood pressure response. These findings suggest that the blood pressure response to senktide is an indirect effect mediated by noradrenaline released from sympathetic nerve endings, whereas the bradycardia is of vagal reflex origin. 4. SR 142801, ((S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl) piperidin-3-yl) propyl)-4-phenyl-piperidin-4-yl)-N-methylacetamide), a potent and specific non-peptide NK3 receptor antagonist dose-dependently (0.46-4.6 mumol kg-1, i.v.; 4.6-46 mumol kg-1, p.o.) inhibited the cardiovascular effects of senktide and displayed a long-lasting inhibitory effect after oral administration. By contrast, SR 142806 (4.6 mumol kg-1, i.v.), the (R)-enantiomer of SR 142801 had no effect on the responses to senktide. SR 142801 at a high dose (15 mumol kg-1, i.v.) was inactive toward the [Sar9, Met(O2)11]SP-induced hypotension. 5. SR 142801 did not modify MAP in conscious guinea-pigs both after i.v. (4.6 and 15 mumol kg-1) and oral (46 and 150 mumol kg-1) administration, showing a lack of agonistic properties. However, a slight reduction in HR was observed only after i.v. injection. 6. In conclusion, these results show evident differences in the functional role of tachykinin receptors in the peripheral control of the cardiovascular system. Furthermore, a clear pressor effect of senktide, which was selectively blocked by SR 142801, was observed in conscious guinea-pigs. Hence, this antagonist appears suitable for investigating the functional role of NK3 receptors.

[Arg8]vasopressin-induced responses of the human isolated coronary artery: effects of non-peptide receptor antagonists.

Contractions induced by [Arg8]vasopressin (vasopressin) and the effect of nonpeptide vasopressin receptor antagonists were studied in the human isolated coronary artery. Vasopressin induced contraction of coronary artery segments with a high pD2 (9.25) but a low Emax (11.8% of the response to 100 mM K+). This response was not affected by removal of the endothelium. Contraction was antagonized by the vasopressin V1 receptor antagonist 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) (pA2: 9.76). OPC-31260 ([5-dimethylamino-1-(4-(2-methylbenzoylamino)benzoyl)-2,3,4,5-tetr ahydro-1H- benzazepine]: vasopressin V2 receptor antagonist) and OPC-21268 (1-(1-[4-(3-acetylaminopropoxy) benzoyl]-4-piperidyl)-3,4- dihydro-2(1H)-quinolinone: reported vasopressin V1 receptor antagonist) were less potent antagonists of vasopressin-induced contractions (pA2: 7.31 and 5.6, respectively). The antagonist potency order (SR 49059 > OPC-31260 > OPC-21268) corresponds to the reported affinity order for the human cloned vasopressin V1 receptor. Therefore, the vasopressin V1 receptor antagonist SR 49059, but not OPC-21268, appears to be an appropriate tool to investigate further the role of vasopressin in pathological processes involving coronary vasoconstriction in humans.

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.