The role of Ca2+ in the control of renin release from dog renal cortical slices

Using a continuous superfusion system of dog renal cortical slices, we studied the role of Ca(2+) in the intracellular control mechanism for renin release. The calcium ionophore A23187 (10 microM) produced a significant decrease in renin release. This effect was abolished in the absence of extracellular Ca(2+). Moreover, pretreatment with the calmodulin inhibitor W-7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, 20 microM) completely prevented the inhibitory effect of A23187 (10 microM). The beta-adrenoceptor agonist isoproterenol (1, 10 and 100 microM) produced a concentration-dependent increase in renin release. Pretreatment with W-7 (20 microM) potentiated the stimulation of renin release induced by isoproterenol (1 microM). These results suggest that A23187-induced inhibition of renin release is mediated by the activation of calmodulin via an increase in intracellular Ca(2+) and beta-adrenoceptor-stimulated renin release is modulated by intracellular Ca(2+) mobilization.

Effect of conivaptan, a combined vasopressin V(1a) and V(2) receptor antagonist, on vasopressin-induced cardiac and haemodynamic changes in anaesthetised dogs

The neurohormonal factor arginine vasopressin (AVP) produces potent systemic vasoconstriction as well as water retention in the kidneys via the V(1a) and V(2) receptors, respectively. Therefore, AVP may be considered as an aggravating factor of cardiac failure. In the present study, the effects of intravenous (i.v.) infusion of AVP on cardiovascular parameters and the effect of conivaptan (YM087, 4'-(2-methyl-1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)-2-phenylbenzanilide monohydrochloride), a vasopressin V(1a)/V(2) receptor antagonist, on AVP-induced cardiac and haemodynamic changes were investigated in pentobarbitone-anaesthetised dogs. The i.v. infusion of AVP (0.12-4mUkg(-1)min(-1)) dose-dependently produced decreases in the cardiac contractility indicator LV dP/dt(max) and cardiac output (CO) and increases in left ventricular end-diastolic pressure (LVEDP) and total peripheral resistance (TPR). These changes accurately mimic the cardiovascular symptoms of congestive heart failure. The i.v. bolus injection of conivaptan (0.1mgkg(-1)) rapidly attenuated the AVP (4mUkg(-1)min(-1))-induced decrease in CO and reversed the AVP-induced elevation in both LVEDP and TPR. In conclusion, i.v. infusion of AVP produced cardiac dysfunction and vasoconstriction in pentobarbitone-anaesthetised dogs. Conivaptan demonstrated the ability to dramatically improve the impaired cardiovascular parameters induced by AVP. The results suggest the potential usefulness of conivaptan in treating congestive heart failure.

Effect of YM471, a nonpeptide AVP receptor antagonist, on human coronary artery smooth muscle cells

The antagonistic properties of YM471, a potent nonpeptide vasopressin (AVP) V(1A) and V(2) receptor antagonist, were characterized using human coronary artery smooth muscle cells (CASMC). YM471 potently inhibited specific binding of 3H-AVP to V(1A) receptors on human CASMC, exhibiting a K(i) value of 0.49 nM. Furthermore, YM471 inhibited the AVP-induced increase in intracellular free Ca(2+) concentration with an IC(50) value of 1.42 nM, but exerted no agonistic activity on CASMC. Additionally, while AVP concentration-dependently induced hyperplasia and hypertrophy in CASMC, YM471 prevented these AVP-induced growth effects, exhibiting IC(50) values of 0.93 and 2.64 nM, respectively. These results indicate that YM471 has high affinity for V(1A) receptors on, and high potency in inhibiting AVP-induced physiologic responses of, human CASMC.

Effect of YM471, an orally active non-peptide arginine vasopressin receptor antagonist, on human vascular smooth muscle cells

OBJECTIVE

To investigate the effects of YM471, a non-peptide arginine vasopressin (AVP) V1A and V2 receptor antagonist, on the AVP-induced growth responses in human vascular smooth muscle cells (VSMCs).

METHODS

Binding of YM471 to V1A receptors on VSMCs was measured using [3H]AVP. Intracellular free Ca2+ concentration was measured by fura 2 fluorescence. Mitogen-activated protein (MAP) kinase activity was determined using the p42/p44 MAP kinase specific peptide and [gamma- 32P]ATP as substrates. The effect of AVP on hyperplasia and hypertrophy of VSMCs was determined by cell number and protein content measurements.

RESULTS

YM471 potently and concentration-dependently inhibited the specific binding of [ 3H]AVP to V1A receptors on VSMCs, exhibiting an inhibition constant (Ki ) of 0.35 nmol/l. YM471 inhibited the AVP-induced increase in intracellular free Ca concentration with an 50% inhibition concentration (IC50 ) of 2.01 nmol/l and inhibited the activation of MAP kinase with an IC50 of 6.11 nmol/l. In addition, AVP concentration-dependently induced hyperplasia and hypertrophy in VSMCs, but YM471 prevented these AVP-induced growth effects, exhibiting IC50 values of 2.31 and 0.23 nmol/l, respectively.

CONCLUSIONS

These results indicate that YM471 has high affinity for V receptors on, and potently inhibits AVP-induced physiologic responses of, human VSMCs.

Effect of the vasopressin receptor antagonist conivaptan in rats with heart failure following myocardial infarction

Myocardial infarction often induces congestive heart failure accompanied by a significant increase in plasma vasopressin concentration. To delineate the role of vasopressin in the pathogenesis of congestive heart failure, the acute hemodynamic and aquaretic effects of conivaptan (YM087, 4'-(2-methyl-1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)-2-phenylbenzanilide monohydrochloride), a combined vasopressin V(1A) and V(2) receptor antagonist, were assessed in rats with heart failure induced by myocardial infarction. Left coronary artery ligation resulted in decreased left ventricular systolic pressure and first derivatives of left ventricular developed pressure, as well as increased left ventricular end-diastolic pressure, lung and right ventricular weight. Single oral administration of conivaptan (0.3 to 3.0 mg/kg) dose-dependently increased urine volume and decreased urine osmolality in heart failure rats. Furthermore, conivaptan (3.0 mg/kg) attenuated the changes in left ventricular end-diastolic pressure, lung and right ventricular weight induced by heart failure while reducing blood pressure. These results show that vasopressin plays a significant role in elevating vascular tone through vasopressin V(1A) receptors and plays a major role in retaining free water through vasopressin V(2) receptors in this model of congestive heart failure. Additionally, conivaptan, with its dual vasopressin V(1A) and V(2) receptor-inhibiting properties, could exert a beneficial effect on cardiac function in the congestive heart failure rat model.

Pharmacological characterization of YM471, a novel potent vasopressin V(1A) and V(2) receptor antagonist

The pharmacologic profile of YM471 ((Z)-4'-[4,4-difluoro-5-[2-(4-dimethylaminopiperidino)-2-oxoethylidene]-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl]-2-phenylbenzanilide monohydrochloride), a novel potent vasopressin V(1A) and V(2) receptor antagonist, was investigated using several in vitro and in vivo techniques. YM471 showed high affinity for rat vasopressin V(1A) and V(2) receptors, exhibiting K(i) values of 0.16 and 0.77 nM, respectively. In contrast, YM471 exhibited much lower affinity for rat vasopressin V(1B) and oxytocin receptors, with K(i) values of 10.5 microM and 31.0 nM, respectively. In conscious rats, oral administration of YM471 (0.1-3.0 mg/kg) produced dose-dependent inhibition of the pressor response caused by exogenous vasopressin and increased urine excretion and decreased urine osmolality; this effect lasted more than 8 h. In all biological assays used, YM471 exhibited no agonistic activity. These results demonstrate that YM471 exerts potent and long-lasting antagonistic activity on both vasopressin V(1A) and V(2) receptors, and that this compound may be a useful tool for clarifying the physiologic and pathophysiologic roles of vasopressin and the therapeutic usefulness of the vasopressin receptor antagonist.

Effects of YM471, a nonpeptide AVP V(1A) and V(2) receptor antagonist, on human AVP receptor subtypes expressed in CHO cells and oxytocin receptors in human uterine smooth muscle cells

YM471, (Z)-4'-[4,4-difluoro-5-[2-(4-dimethylaminopiperidino)-2-oxoethylidene]-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl]-2-phenylbenzanilide monohydrochloride, is a newly synthesized potent vasopressin (AVP) receptor antagonist. Its effects on binding to and signal transduction by cloned human AVP receptors (V(1A), V(1B) and V(2)) stably expressed in Chinese hamster ovary (CHO) cells, and oxytocin receptors in human uterine smooth muscle cells (USMC) were studied. YM471 potently inhibited specific [(3)H]-AVP binding to V(1A) and V(2) receptors with K(i) values of 0.62 nM and 1.19 nM, respectively. In contrast, YM471 exhibited much lower affinity for V(1B) and oxytocin receptors with K(i) values of 16.4 microM and 31.6 nM, respectively. In CHO cells expressing V(1A) receptors, YM471 potently inhibited AVP-induced intracellular Ca(2+) concentration ([Ca(2+)](i)) increase, exhibiting an IC(50) value of 0.56 nM. However, in human USMC expressing oxytocin receptors, YM471 exhibited much lower potency in inhibiting oxytocin-induced [Ca(2+)](i) increase (IC(50)=193 nM), and did not affect AVP-induced [Ca(2+)](i) increase in CHO cells expressing V(1B) receptors. Furthermore, in CHO cells expressing V(2) receptors, YM471 potently inhibited the production of cyclic AMP stimulated by AVP with an IC(50) value of 1.88 nM. In all assays, YM471 showed no agonistic activity. These results demonstrate that YM471 is a potent, nonpeptide human V(1A) and V(2) receptor antagonist which will be a valuable tool in defining the physiologic and pharmacologic actions of AVP.

Norepinephrine release is increased in the hibernating heart, studied in a chronic canine model of myocardial hibernation

We examined the change in cardiac sympathetic function in the hibernating heart. To induce hibernating hearts in dogs, we placed a nylon tube via the carotid artery in the left circumflex artery (LCx) and obstructed the LCx flow. The plasma norepinephrine (NE) and epinephrine (E) concentrations in the coronary sinus and the aorta were measured before and 1 week after the tube placement to evaluate the catecholamine release from the heart. The wall motion was followed by echocardiography and. 1 week after the tube placement, regional myocardial blood flow (RBF) was measured using colored microspheres. Also. the restorability of myocardial dysfunction was examined in other dogs by extracting the LCx tube 1 week after the placement. Finally, the heart was removed for pathological observation and dogs showing myocardial infarction were excluded. One week after placing the tube, wall thickening was reduced in the LCx area, but was not in the left anterior descending (LAD) area. Compared with the LAD area, RBF in the LCx area was decreased in the endocardium (p < 0.05), but was not in the epicardium. In other dogs, the reduced wall thickening in the LCx area was restored to normal levels 1 or 2 weeks after the tube extraction. Thereby, our dogs with the tube placed were considered to be models of myocardial hibernation. The plasma NE and E concentrations were not significantly changed by placing the tube, but NE release from the heart was increased after the tube placement (p < 0.05). E uptake from the heart did not differ. Therefore, it is suggested that NE release is increased in the hibernating heart and may contribute to its mechanism.

Highly potent and orally active non-peptide arginine vasopressin antagonists for both V1A and V2 receptors: synthesis and pharmacological properties of 4'-[(4,4-difluoro-5-methylidene-2,3,4,5-tetrahydro-1H-1-benzoazepin-1-y l)carbonyl]-2-phenylbenzanilide derivatives

A series of compounds structurally related to 4'-[(4,4-difluoro-5-methylidene-2,3,4,5-tetrahydro-1H-1-benzoaz epin-1-yl) carbonyl]-2-phenylbenzanilide were synthesized and evaluated for arginine vasopressin (AVP) antagonistic activity. Compounds with a (Z)-olefin geometry at the 5-position of benzoazepine possessed potent affinity for both the V1A and V2 receptors. Further study has shown that one of these derivatives, (Z)-4'-(¿4,4-difluoro-5-[(4-dimethylaminopiperidino)carbonylmet hylene]-2,3,4,5-tetrahydro-1H-1-benzoazepin-1-yI¿carbonyl)2- phenylbenzanilide monohydrochloride (29, YM-35471), exhibits exceptionally potent affinity for both of V1A and V2 receptors, even when administered orally. The synthesis and pharmacological properties of this compound are detailed in this paper.

Nonpeptide arginine vasopressin antagonists for both V1A and V2 receptors: synthesis and pharmacological properties of 4-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)benzanili de derivatives and 4'-(5,6-dihydro-4H-thiazolo[5,4-d][1]benzoazepine-6-carbonyl)benzanilid e derivatives

Arginine vasopressin (AVP) has a dual action mainly in the periphery, i.e., vasoconstriction and water reabsorption via V1A and V2 receptors; it may play a role in a number of diseases, including congestive heart failure (CHF), hypertension, renal disease, edema, and hyponatremia. We have attempted to develop a new series of orally active AVP antagonists for both V1A and V2 receptors based on the hypothesis that the blockade of both V1A and V2 receptors might be beneficial to CHF patients. In this report, a series of compounds structurally related to 4'-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6- carbonyl)benzanilide and 4'-(5,6-dihydro-4H- thiazolo[5,4-d][1]benzoazepine-6-carbonyl)benzanilide were synthesized and examined for AVP antagonist activity for both V1A and V2 receptors. As a result, it was found that the 4'-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbon yl)-2- phenylbenzanilide derivatives showed potent binding affinity for both V1A and V2 receptors. Especially, 4'-(2-methyl-1,4,5,6- tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)-2-phe nylbenzanilide monohydrochloride (18, YM087 = conivaptan hydrochloride) exhibited potent binding affinity and AVP antagonist activity, after intravenous administration, for both V1A and V2 receptors. Furthermore, YM087 exhibited the most potent oral activity for the V2 receptor. Details of the synthesis and pharmacological properties of this series are presented.

Pharmacologic characterization of the oxytocin receptor in human uterine smooth muscle cells

[(3)H]-oxytocin was used to characterize the oxytocin receptor found in human uterine smooth muscle cells (USMC). Specific binding of [(3)H]-oxytocin to USMC plasma membranes was dependent upon time, temperature and membrane protein concentration. Scatchard plot analysis of equilibrium binding data revealed the existence of a single class of high-affinity binding sites with an apparent equilibrium dissociation constant (K(d)) of 0.76 nM and a maximum receptor density (B(max)) of 153 fmol mg(-1) protein. The Hill coefficient (n(H)) did not differ significantly from unity, suggesting binding to homogenous, non-interacting receptor populations. Competitive inhibition of [(3)H]-oxytocin binding showed that oxytocin and vasopressin (AVP) receptor agonists and antagonists displaced [(3)H]-oxytocin in a concentration-dependent manner. The order of potencies for peptide agonists and antagonists was: oxytocin>[Asu(1,6)]-oxytocin>AVP= atosiban>d(CH(2))(5)Tyr(Me)AVP>[Thr(4),Gly(7)]-oxytocin>dDAVP, and for nonpeptide antagonists was: L-371257>YM087>SR 49059>OPC-21268>SR 121463A>OPC-31260. Oxytocin significantly induced concentration-dependent increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) and hyperplasia in USMC. The oxytocin receptor antagonists, atosiban and L-371257, potently and concentration-dependently inhibited oxytocin-induced [Ca(2+)](i) increase and hyperplasia. In contrast, the V(1A) receptor selective antagonist, SR 49059, and the V(2) receptor selective antagonist, SR 121463A, did not potently inhibit oxytocin-induced [Ca(2+)](i) increase and hyperplasia. The potency order of antagonists in inhibiting oxytocin-induced [Ca(2+)](i) increase and hyperplasia was similar to that observed in radioligand binding assays. In conclusion, these data provide evidence that the high-affinity [(3)H]-oxytocin binding site found in human USMC is a functional oxytocin receptor coupled to [Ca(2+)](i) increase and cell growth. Thus human USMC may prove to be a valuable tool in further investigation of the physiologic and pathophysiologic roles of oxytocin in the uterus. British Journal of Pharmacology (2000) 129, 131 - 139

Characterization of rodent liver and kidney AVP receptors: pharmacologic evidence for species differences

Radioligand binding studies with [3H]vasopressin (AVP) were used to determine the affinities of AVP receptor agonists and antagonists for mouse liver and kidney plasma membrane preparations. Both membrane preparations exhibited one class of high-affinity binding site. AVP ligand binding inhibition studies confirmed that mouse liver binding sites belong to the V1A subtype while kidney binding sites belong to the V2 receptor subtype. The affinity of each ligand for mouse V1A receptors was very similar to that for rat V1A receptors, showing differences in Ki values of less than 3-fold. In contrast, several peptide (d(CH2)5Tyr(Me)AVP) and nonpeptide (OPC-21268 and SR 49059) ligands had different affinities for mouse and rat kidney V2 receptors, with differences in Ki values ranging from 14- to 17-fold. These results indicate that mouse and rat kidney V2 receptors show significant pharmacologic differences.

[Pharmacology of conivaptan hydrochloride (YM087), a novel vasopressin V1A/V2 receptor antagonist]

Pharmacology of conivaptan hydrochloride (YM087) was investigated in in vitro and in vivo studies. In radioligand binding study, YM087 showed high affinity for both V1A and V2 receptors in animal and human species. Affinity of YM087 for V1A and V2 receptors was comparable to that of vasopressin (AVP). In functional antagonistic activity study, YM087 concentration-dependently inhibited AVP-induced intracellular Ca2+ elevation via human V1A receptors and AVP-stimulated cAMP accumulation via human V2 receptors. Intravenous administration of YM087 dose-dependently inhibited AVP-induced pressor responses and produced a dose-dependent aquaresis in rats and dogs. Oral administration of YM087 showed a potent and long-lasting antagonistic activity on V1A and V2 receptors. YM087 was effective in dogs with heart failure and in heart failure rats with hyponatremia and edema. These results reveal that YM087 is the first orally active V1A/V2 receptor antagonist and suggest that YM087 may be useful in the treatment of congestive heart failure and hyponatremia.

Comparison of vasopressin binding sites in human uterine and vascular smooth muscle cells

Several studies indicate that oxytocin and vasopressin receptors in the human uterus are heterogeneous. We have investigated whether oxytocin and vasopressin bind to separate receptors or one class of receptors in human uterine smooth muscle cells. [3H]d(CH2)5Tyr(Me)AVP, the vasopressin V1A receptor selective radioligand, was used for comparison of vasopressin binding sites in human uterine and vascular smooth muscle cell membranes. Both membrane preparations exhibited one class of high-affinity binding sites with Kd values of 6.44 and 0.47 nM, Bmax values of 166 and 34.8 fmol/mg protein for uterine and vascular smooth muscle cells, respectively. In vascular preparations, the selective vasopressin V1A receptor antagonist, SR 49059 ((2S) 1-[(2R 3S)-(5-chloro-3-(2-chlorophenyl)- -(3.4-dimethoxybenzenesulfonyl)-3-hydroxy-2,3-dihydro-1H-indole-2- carbonyl]-pyrrolidine-2-carboxamide), showed high affinity with Ki value of 0.98 nM, confirming that these receptors belong to the vasopressin V1A receptor subtype. On the contrary, in uterine preparations, binding of [3H]d(CH2)5Tyr(Me)AVP was more effectively displaced by oxytocin and the oxytocin receptor selective antagonist, L-371257, (1-[1-[4-[ N-Acetyl-4-piperidinyl)oxy]2-methoxybenzoyl]piperidin-4-yl]- 4H-3,1-benzoxazin-2(1H)-one), than vasopressin and SR 49059, suggesting that binding may be due to cross-reaction with the oxytocin receptors. These results suggest that human uterine smooth muscle cells express only a high density of oxytocin receptors.

Cardiovascular and renal effects of conivaptan hydrochloride (YM087), a vasopressin V1A and V2 receptor antagonist, in dogs with pacing-induced congestive heart failure

The systemic hemodynamic and renal responses to conivaptan hydrochloride (YM087; 4'-(2-methyl-1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine -6-carbonyl)-2-phenylbenzanilide monohydrochloride), a vasopressin V1A and V2 receptor antagonist, were determined in pentobarbital-anesthetized dogs after 2 to 3 weeks of rapid right ventricular pacing. Congestive heart failure, characterized by decreases in first derivative of left ventricular pressure (left ventricular d P/dt(max)) and cardiac output, and increases in left ventricular end-diastolic pressure and total peripheral vascular resistance, was induced by chronic rapid right ventricular pacing at 260-280 beats/min. Intravenous administration of conivaptan (0.1 mg/kg) significantly increased left ventricular dP/dt(max) and cardiac output and significantly decreased left ventricular end-diastolic pressure and total peripheral vascular resistance. Conivaptan also increased urine flow and reduced urine osmolality by markedly increasing free water clearance. These results indicate that conivaptan produced hemodynamic improvement and marked aquaresis in dogs with congestive heart failure. Therefore, conivaptan may find clinical use in treating patients with congestive heart failure.

Pharmacological profile of orally administered YM087, a vasopressin antagonist, in conscious rats

1. YM087 is a newly synthesized non-peptide arginine vasopressin (AVP) antagonist that shows high affinity for both V1A and V2 receptors. In the present study, the V1A and V2 receptor antagonist effects of orally administered YM087 were assessed in conscious rats. 2. In conscious rats, orally administered YM087 (0.1, 0.3 and 1.0 mg/kg) did not affect basal blood pressure, but YM087 dose-dependently inhibited 30 mU/kg, i.v., AVP-induced pressor responses. This inhibition lasted for over 8 h following the oral administration of the highest dose of YM087 (1 mg/kg). 3. In rats deprived of water and food for 16-18 h, oral administration of YM087 (0.1, 0.3, 1 and 3 mg/kg) dose-dependently increased urine volume and reduced urine osmolality, with associated increases in urinary sodium and potassium excretion. However, these increases in electrolyte excretion were lower than those seen at comparable diuretic doses of furosemide (3, 10, 30 and 100 mg/kg, p.o.). 4. Oral administration of YM087 (0.3, 1 and 3 mg/kg) produced a dose-dependent increase in urine volume in rats allowed free access to water, with the diuretic effect peaking 2-4 h post-dosing at all dose levels. The diuretic effect of YM087 was sustained 8-10 h after a dose of 3 mg/kg; this is in contrast with the transient diuresis seen after furosemide (100 mg/kg, p.o.) dosing. 5. The present results demonstrate that YM087 is an orally active AVP antagonist with potent and long-lasting effects. YM087 suppressed V1A receptor-mediated pressor responses to AVP with minimal effects on basal haemodynamics and exerted a diuretic effect without increased electrolyte excretion by inhibiting V2 receptor-mediated water reabsorption.

Nonpeptide arginine vasopressin antagonists for both V1A and V2 receptors: synthesis and pharmacological properties of 4'-[5-(substituted methylidene)-2,3,4,5-tetrahydro-1H-1-ben zoazepine-1-carbonyl]benzanilide and 4'-[5-(substituted methyl)-2,3-dihydro-1H-1-benzoazepine-1- carbonyl]benzanilide derivatives

Arginine vasopressin (AVP) has a dual action, i.e. vasoconstriction and water reabsorption via V1A and V2 receptors, and may play a role in a number of diseases, including congestive heart failure (CHF), hypertension, renal disease, edema, and hyponatremia. We have attempted to develop a new series of AVP antagonists for both V1A and V2 receptors based on the hypothesis that the blockade of both V1A and V2 receptors might be beneficial to CHF patients. In this report, a series of compounds structurally related to 4'-[5-(substituted methylidene)-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl ]benzanilide (exo-olefin isomer) and 4'-[5-(substituted methyl)-2,3-dihydro-1H-1-benzoazepine-1-carbonyl]benzanilide (endo-olefin isomer) were synthesized and examined to have AVP antagonist activity for both V1A and V2 receptors. As a result, it was found that the (E)-exo-olefin isomers showed more potent binding affinity compared with endo-olefin isomers. Among these (E)-exo-olefin isomers, (E)-N-methyl-{1-[4-(2-methylbenzoylamino)benzoyl]-2,3,4,5-tetrahyd ro-1H-1 -benzoazepin-5-ylidene}acetamide (14) exhibited the most potent binding affinity and (E)-N-methyl-(1-{4-[2-(4-methylphenyl)benzoylamino]benzoyl}-2,3,4,5- tetrahydro-1H-1-benzoazepin-5-ylidene)acetamide (20) exhibited a high AVP antagonist activity for both V1A and V2 receptors after intravenous administration. Details of the synthesis and pharmacological properties of this series are presented.

Vasopressin increases vascular endothelial growth factor secretion from human vascular smooth muscle cells

Vascular endothelial growth factor (VEGF) is a potent and specific mitogen of vascular endothelial cells which promotes neovascularization in vitro. To determine whether vasopressin induces VEGF secretion in human vascular smooth muscle cells, we performed enzyme-linked immunosorbent assays. Vasopressin potently induced a time-dependent and concentration-dependent (maximal, 10(-7) M) increase in VEGF secretion by human vascular smooth muscle cells that was maximal after 24 h. Furthermore, vasopressin also concentration-dependently caused mitogenic effect, as reflected by total protein content of cells per culture well. These vasopressin-induced VEGF secretion increase and mitogenic effect of these cells were potently inhibited by vasopressin V1A receptor antagonists, confirming this is a vasopressin V1A receptor-mediated event. These results indicate that vasopressin increases VEGF secretion in human vascular smooth muscle cells, the magnitude of VEGF secretion being temporally related to the mitogenic effect of vascular smooth muscle cells and the potency of the growth-promoting stimulus. Vasopressin-induced VEGF secretion by proliferating vascular smooth muscle cells could act as a paracrine hormone to powerfully influence the permeability and growth of the overlying vascular endothelium, vasopressin play a more fundamental role in the regulation of vascular function than has previously been recognized.

AVP-induced mitogenic responses of Chinese hamster ovary cells expressing human V1A or V1B receptors

Arginine vasopressin (AVP) induces cell proliferation and hypertrophy; however, the human receptor subtype and the intracellular signaling pathways responsible for this mitogenic activity remain unclear. Experiments were conducted to determine which AVP receptor is linked to mitogen-activated protein (MAP) kinase activation and the mitogenic effect seen in Chinese hamster ovary (CHO) cells expressing human V1A or V1B receptors. Adding AVP to CHO cells transfected with human V1A or V1B cDNA significantly and concentration-dependently induced activation of MAP kinase and increased DNA synthesis, as measured by [3H]thymidine incorporation. These effects were inhibited by AVP receptor antagonists and the potency order of antagonists in vitro was similar to that observed in radioligand binding assays. These results suggest that AVP induces the MAP kinase cascade leading to cell proliferation through either human V1A or V1B receptors, and that these cloned, expressed AVP receptors may prove an invaluable tool for probing the physiologic and pathophysiologic effects of AVP.

Pharmacological characterization of the human vasopressin receptor subtypes stably expressed in Chinese hamster ovary cells

Three subtypes of human (h) arginine vasopressin (AVP) receptors, hV1A, hV1B and hV2, were stably expressed in Chinese hamster ovary (CHO) cells and characterized by [3H]-AVP binding studies. In addition, the coupling of the expressed receptor protein to a variety of signal transduction pathways was investigated. Scatchard analysis of saturation isotherms for the specific binding of [3H]-AVP to membranes, prepared from CHO cells transfected with hV1A, hV1B and hV2 receptors, yielded an apparent equilibrium dissociation constant (Kd) of 0.39, 0.25 and 1.21 nM and a maximum receptor density (Bmax) of 1580 fmol mg(-1) protein, 5230 fmol mg(-1) protein and 7020 fmol mg(-1) protein, respectively. Hill coefficients did not differ significantly from unity, suggesting binding to homogenous, non-interacting receptor populations. Pharmacological characterization of the transfected human AVP receptors was undertaken by measuring the relative ability of nonpeptide AVP receptor antagonists, YM087, OPC-21268, OPC-31260, SR 49059 and SR 121463A, to inhibit binding of [3H]-AVP. At hV1A receptors, the relative order of potency was SR49059>YM087>OPC-31260>SR 121463A> >OPC-21268 and at hV2 receptors, YM087=SR 121463A>OPC-31260>SR 49059> >OPC-21268. In contrast, the relative order of potency, at hV1B receptors, was SR 49059> >SR 121463A=YM087=OPC-31260=OPC-21268. In CHO cells expressing either hV1A or hV1B receptors, AVP caused a concentration-dependent increase in intracellular Ca2+ concentration ([Ca2+]i) with an EC50 value of 1.13 nM and 0.90 nM, respectively. In contrast, stimulation of CHO cells expressing hV2 receptors resulted in an accumulation of cyclic AMP with an EC50 value of 2.22 nM. The potency order of antagonists in inhibiting AVP-induced [Ca2+]i or cyclic AMP response was similar to that observed in radioligand binding assays. In conclusion, we have characterized the pharmacology of human cloned V1A, V1B and V2 receptors and used these to determine the affinity, selectivity and potency of nonpeptide AVP receptor antagonists. Thus they may prove to be a valuable tool in further examination of the physiological and pathophysiological roles of AVP.

Effect of YM435, a dopamine DA1 receptor agonist, in a canine model of ischemic acute renal failure

1. The effects of (-)-(S)-4-(3,4-dihydroxyphenyl)- 1,2,3,4-tetrahydroisoquinoline-7,8-diol monohydrochloride monohydrate (YM435), a dopamine DA1 receptor agonist, were evaluated in a canine model of ischemic acute renal failure (ARF). 2. ARF was induced by clamping the left renal artery for 1 hr and subsequent reperfusion of the left kidney in anesthetized uninephrectomized dogs. 3. After 1-hr complete renal artery occlusion, an intravenous infusion of either YM435 (0.3 microg/kg/ min) or 0.9% saline (vehicle) was begun and continued for 1 hr. 4. In the vehicle group, renal ischemia markedly decreased glomerular filtration rate, urine flow and urinary sodium excretion. The YM435 group was characterized by significant recoveries in glomerular filtration rate, urine flow, and urinary sodium excretion as compared with the vehicle group. 5. These results indicate that YM435 can facilitate recovery in glomerular filtration rate, urine flow, and urinary sodium excretion in a canine model of ARF induced by ischemia. YM435 may be useful in the preservation of renal function in ischemia-induced ARF.

Nonpeptide arginine vasopressin antagonists for both V1A and V2 receptors: synthesis and pharmacological properties of 2-phenyl-4'-(2,3,4,5-tetrahydro-1H-1,5-benzodiazepine-1-carbonyl) benzanilide derivatives

A series of compounds structurally related to 2-phenyl-4'-(2,3,4,5-tetrahydro-1H-1,5-benzodiazepine-1-carbonyl) benzanilide was synthesized and demonstrated to have arginine vasopressin (AVP) antagonist activity for both V1A and V2 receptors. The introduction of a hydrophilic substituent group into the 5-position of the benzodiazepine ring resulted in an increase in oral availability. Especially, the (3-pyridyl)methyl (31b), the 2-(4-methyl-1,4-diazepan-1-yl)-2-oxoethyl (32i), and the 2-(4-methylpiperazin-1-yl)ethyl (33g) derivatives exhibited high antagonist activities and high oral availability. Details of the synthesis and pharmacological properties of this series are presented.

Characterization of vasopressin receptor in rat lung

This study characterized rat lung membrane arginine vasopressin (AVP) receptors in detail. Specific binding of [3H]AVP to rat lung membranes was dependent upon time, temperature and membrane protein concentration. Scatchard plot analysis of equilibrium binding data revealed the existence of a single class of high-affinity binding sites with a Kd of 0.45 nM and a Bmax of 76.6 fmol/mg protein. Competitive inhibition of [3H]AVP binding showed that neurohypophysial hormones as well as their synthetic analogues displaced [3H]AVP in a concentration-dependent manner. The order of potencies for the native peptides was: AVP > lysine vasopressin = arginine vasotocin > oxytocin. Furthermore, potent V1A receptor antagonists, d(CH2)5Tyr(Me)AVP and dPTyr(Me)AVP, showed high affinity for lung membranes. In contrast, the V2 receptor agonist, dDAVP, and the specific oxytocin receptor agonist, [Thr4,Gly7]oxytocin, did not affect AVP binding. These results suggest that the lung contains the V1A receptor subtype. The lung membrane AVP receptor characterized in this study may play an important role in mediating the physiological effects of AVP in the lung.

Effect of YM435, a novel dopamine DA1 receptor agonist, in a canine model of acute congestive heart failure

1. The effects of YM435, a dopamine DA1 receptor agonist, were evaluated in a canine model of acute congestive heart failure. 2. The model was induced in open-chest anesthetized dogs by left anterior descending coronary artery ligation, volume loading, and intravenous infusion of angiotensin II. This resulted in a moderate and stable congestive heart failure characterized by reduction in cardiac output and increases in left ventricular end-diastolic pressure and total peripheral vascular resistance. 3. Intravenous infusion of YM435 (1 microgram/kg/min) significantly decreased left ventricular end-diastolic pressure, total peripheral vascular resistance and mean blood pressure and significantly increased cardiac output and renal blood flow in this model. 4. These results indicate that intravenous infusion of YM435 can improve hemodynamics and cardiac function in a canine model of acute congestive heart failure. YM435 may be a useful therapeutic agent for the treatment of congestive heart failure.