Effects of OPC-21268, an orally effective vasopressin V1 receptor antagonist in humans

Inhibitory effect of vasopressin receptor antagonist OPC-31260 on experimental brain oedema induced by global cerebral ischaemia

The effects of the non-peptide vasopressin V(2) receptor antagonist 5-dimethylamino-1-[4-(2-methylbenzoylamino)benzoyl]-2,3,4,5-tetrahydro-1H-benzazepine hydrochloride (OPC-31260) on the cerebral oedema induced by general cerebral hypoxia were studied in rats. The general cerebral hypoxia was produced by bilateral common carotid ligation in Sprague-Dawley rats of the CFY strain. By 6 h after the ligation, half of the rats had died, but the survival rate was significantly higher following OPC-31260 administration. Electron microscopic examinations revealed typical ischaemic changes after the carotid ligation. The carotid ligation increased the brain contents of water and Na(+) and enhanced the plasma vasopressin level. The increased brain water and Na(+) accumulation was prevented by OPC-31260 administration, but the plasma vasopressin level was further enhanced by OPC-31260. These results demonstrate the important role of vasopressin in the development of the disturbances in brain water and electrolyte balance in response to general cerebral hypoxia. The carotid ligation-induced cerebral oedema was significantly reduced following oral OPC-31260 administration. The protective mechanism exerted by OPC-31260 stems from its influence on the renal vasopressin V(2) receptors. These observations might suggest an effective approach to the treatment of global hypoxia-induced cerebral oedema in humans.

Oxytocin, vasopressin, and autism: is there a connection?

Autism is a poorly understood developmental disorder characterized by social impairment, communication deficits, and compulsive behavior. The authors review evidence from animal studies demonstrating that the nonapeptides, oxytocin and vasopressin, have unique effects on the normal expression of species-typical social behavior, communication, and rituals. Based on this evidence, they hypothesize that an abnormality in oxytocin or vasopressin neurotransmission may account for several features of autism. As autism appears to be a genetic disorder, mutations in the various peptide, peptide receptor, or lineage-specific developmental genes could lead to altered oxytocin or vasopressin neurotransmission. Many of these genes have been cloned and sequenced, and several polymorphisms have been identified. Recent gene targeting studies that alter expression of either the peptides or their receptors in the rodent brain partially support the autism hypothesis. While previous experience suggests caution in hypothesizing a cause or suggesting a treatment for autism, the available preclinical evidence with oxytocin and vasopressin recommends the need for clinical studies using gene scanning, pharmacological and neurobiological approaches.

Treatment of brain edema with a nonpeptide arginine vasopressin V1 receptor antagonist OPC-21268 in rats

OBJECTIVE

Recent experimental evidence suggests that centrally released arginine vasopressin plays a significant role in brain capillary water permeability as well as in pathogenesis of vasogenic brain edema. The purpose of this study was to examine the effects of orally administered OPC-21268, a nonpeptide arginine vasopressin V1 receptor antagonist, on cold-induced brain edema in rats.

METHODS

Cold brain injury was induced for 1 minute in 140 rats. Treatment with OPC-21268, at dosages of 100 mg (n = 20), 200 mg (n = 20), and 300 mg/kg (n = 15), or with saline (n = 17) was started 1 hour after the induction of cold injury and was continued every 8 hours for 24 hours. Two percent Evans blue in saline (1 ml/kg) was administered intravenously before cold injury in another group of rats, 15 of which were saline-treated and 55 of which were OPC-21268-treated at the above dosages. After 24 hours, brain tissue water and electrolytes, brain tissue swelling, blood-brain barrier permeability to Evans blue, and plasma electrolytes and osmolality were determined.

RESULTS

Compared with the saline-treated group, OPC-21268 treatment at the dosages of 200 and 300 mg/kg significantly reduced brain water content in both hemispheres (P<0.01). Swelling of the traumatized hemispheres was also significantly reduced at 200 and 300 mg/kg dosages (P<0.05). Brain tissue sodium content was significantly reduced at the dosage of 300 mg/kg (P<0.05). Blood-brain barrier permeability to Evans blue was significantly decreased in a dose-dependent manner compared with the saline-treated group (P<0.01). No significant changes were observed in other parameters.

CONCLUSION

Our results indicate that OPC-21268 predominantly exerts a protective effect in areas where the maximum amount of blood-brain barrier breakdown occurs, and it is effective in the treatment of cold-induced vasogenic brain edema.

Effects of SR 49059, a new orally active and specific vasopressin V1 receptor antagonist, on vasopressin-induced vasoconstriction in humans

We have evaluated the efficacy of SR 49059, a new orally active and specific vasopressin V1 receptor antagonist (arginine-vasopressin [AVP]), in the blockade of the vascular effects of exogenous AVP in healthy subjects. In preliminary experiments, two procedures to measure the V1 vascular effects of AVP were assessed. First, the AVP-induced changes in skin blood flow were investigated by the injection of increasing doses of AVP intradermally, with or without a previous local vasodilation with calcitonin gene-related peptide (CGRP). In a second protocol, AVP was infused intra-arterially, and the changes in radial artery diameter and blood flow were measured. The intradermal injection of AVP caused significant decreases in skin blood flow, and the use of CGRP increased the sensitivity of the method by a factor of 10(2) to 10(3). AVP infused intra-arterially caused dose-dependent decreases in the radial artery diameter and blood flow. In the main study, the potency and efficacy of SR 49059 to block the AVP-induced changes in skin blood flow were assessed in 12 healthy men with a double-blind, triple crossover study design. The subjects were randomized to receive a placebo orally and 30 mg and 300 mg of the antagonist at a 1-week interval. The subjects were then further randomized to evaluate the efficacy of the same doses of the antagonist to block the vasoconstriction of the radial artery induced by an intra-arterial infusion of AVP. SR 49059 inhibits, dose-dependently and significantly, the AVP-induced changes in skin blood flow, with a peak effect occurring between 2 and 6 hours after injection. In addition, the 300-mg dose of SR 49059 completely blocked the vasoconstriction of the radial artery induced by AVP. In conclusion, skin blood-flow measurement, after intradermal injection of AVP on a skin area vasodilated with CGRP, is an effective method to investigate the V1 vascular effect of AVP in humans. SR 49059 is a potent and specific antagonist of V1 receptors, which blocks the AVP-induced vasoconstriction.

Receptor subtype for vasopressin-induced release of nitric oxide from rat kidney

The vasopressin receptor subtype that causes nitric oxide (NO) release remains controversial. To elucidate this receptor-ligand interaction, we examined the effects of vasopressin receptor antagonists on vasopressin-induced release of NO from isolated perfused rat kidneys by using a sensitive chemiluminescence assay. Vasopressin increased renal perfusion pressure and NO signals in the perfusate in a dose-dependent manner. N omega-Monomethyl-L-arginine abolished this increase in NO release; however, a similar increase in renal perfusion pressure induced by prostaglandin F2 alpha was not associated with the increase in NO release. OPC-21268, a V1 receptor antagonist, significantly reduced the vasopressin-evoked renal vasoconstriction and NO release, whereas OPC-31260, a V2 receptor antagonist, had no effects. Moreover, desmopressin, a selective V2 receptor agonist, did not increase the NO signal. NO release by vasopressin was markedly attenuated in deoxycorticosterone acetate (DOCA)-salt hypertensive rat kidneys compared with control kidneys (10(-10) mol/L vasopressin: +0.8 +/- 0.3 versus +6.9 +/- 1.4 fmol/min per gram kidney, DOCA versus control; P < .001). Histochemical analysis for renal NO synthase revealed a substantial attenuation of the staining of endothelial NO synthase in DOCA-salt rats. These results directly demonstrate that vasopressin stimulates NO release via the endothelial V1 receptor in the rat kidney.

Role of vasopressin in neurocardiogenic responses to hemorrhage in conscious rats

Vasovagal reflexes, such as hypotension and bradycardia, are induced by rapid hemorrhage and mimic neurocardiogenic reflexes in mammals. We examined the role of vasopressin in the neurocardiogenic responses to mild, rapid hemorrhage (1 mL/100 g for 30 seconds) and severe hemorrhage (1 mL/100 g body wt for 30 seconds repeated three times at 11-minute intervals) in homozygous Brattleboro and Long-Evans rats. Mild, rapid hemorrhage induced severe bradycardia and hypotension only in Long-Evans rats. Exogenous vasopressin (1.85 pmol/kg per minute for 1 hour) restored both the bradycardic and hypotensive responses in Brattleboro rats. DDAVP, a vasopressin V2-receptor agonist (0.19 pmol/kg per minute for 24 hours), did not affect the cardiovascular responses to hemorrhage in Brattleboro rats, although it maintained urine production within normal limits. However, OPC-31260 (21.6 mumol/kg IV), a vasopressin V2-receptor antagonist, attenuated both the hypotensive and bradycardic responses to hemorrhage in Long-Evans rats. A vasopressin V1-receptor antagonist attenuated bradycardia and delayed the recovery of arterial pressure after hemorrhage but did not affect the hypotension that occurred immediately after hemorrhage in Long-Evans rats. Methylatropine also attenuated both the bradycardic and hypotensive responses induced by hemorrhage, but propranolol had no effect on the cardiovascular responses to hemorrhage in Long-Evans rats. The recovery of arterial pressure after repeated hemorrhage was less adequate in Brattleboro rats than in Long-Evans rats. Our results suggest that the neurocardiogenic responses to hemorrhage, especially hypotension, may be related to vasodilation induced by a V2-receptor-mediated mechanism and by the vagal reflex, both of which are substantiated by the existence of vasopressin. The coexistence of V1- and V2-receptor mechanisms may be necessary for the hypotensive response to hemorrhage. We found that a V2-receptor antagonist attenuated the hypotension mediated by the so-called neurocardiogenic reflex.

Improved skin blood flow and cutaneous temperature in the foot of a patient with arteriosclerosis obliterans by vasopressin V1 antagonist (OPC21268). A case report

A seventy-four-year-old woman with arteriosclerosis obliterans, diabetes mellitus, and hypertension was admitted for the treatment of intermittent claudication and coldness and pain in the right lower extremity. After the administration of a vasopressin V1 antagonist, OPC21268, the symptoms were markedly improved. Furthermore, blood flow in the dorsalis pedis artery and the cutaneous temperature in the right foot increased in response to acute and chronic administration of OPC21268. OPC21268 may be a new useful therapeutic tool for the treatment of arteriosclerosis obliterans.

OPC-21268 antagonizes arginine vasopressin-induced vasoconstrictor response in the spinally-anesthetized dog

We studied the antagonistic actions of OPC-21268 (1-(1-[4-(3-acetylaminopropoxy)-benzoyl]-4-piperidyl)-3,4-dihydro- 2(1H)-quinolinone) on the arginine vasopressin (AVP)-induced vasoconstrictor response in the spinally-anesthetized dog. OPC-21268 at doses of 0.3, 1.0 and 3.0 mg/kg, i.v. produced a rightward parallel shift of the dose-response curves for AVP in a dose-dependent manner. The doses of OPC-21268 were similar to those that inhibited the AVP-induced vasoconstrictor response in the rat. This observation suggests that OPC-21268 acts as a V1-AVP-receptor antagonist in peripheral resistance vessels in dogs as well as in rats.

Beyond ACE inhibition: new developments in drug therapy for hypertension

The growing list of vasoactive substances known to be involved in blood pressure control provides new targets for antihypertensive drugs. Currently under development are alternative strategies for blockade of the renin-angiotensin system (e.g., renin inhibition and angiotensin II receptor antagonism) that may have fewer side effects than angiotensin-converting-enzyme inhibition, and antagonists to other vasocontrictor peptides, such as endothelin and vasopressin. Novel strategies to enhance the effects of endogenous vasodilators, such as natriuretic peptides and nitric oxide, are also being explored.

Effect of nonpeptide vasopressin receptor antagonists on developing, and established DOCA-salt hypertension in rats

Efficacy of orally available, selective vasopressin V1 and V2 receptor antagonists on the developing and established stage of DOCA-salt hypertension was investigated. Twenty-nine Wistar rats were heminephrectomized, and administered DOCA (50 mg/kg; intraperitoneally twice a week) and salt (5% NaCl diet) from week 0 to the end of study. Group 1 rats were served as control. Group 2 and 5 rats were given a V1 antagonist, and groups 3 and 6 rats were given a V2 antagonist, while groups 4 and 7 rats received both V1 and V2 antagonists. Each drug was started to groups 2, 3 and 4 at week 0, and to groups 5, 6 and 7 at week 4. Significant amelioration of the increase in blood pressure was observed in groups 3 and 4 at week 10, and a reduction in blood pressure occurred in groups 6 and 7 at week 10. Otherwise, a V1 antagonist alone slightly attenuated blood pressure rise in the group 2 without significance, and failed to lower blood pressure of the group 5 during the study. These results suggest that both V1 and V2 agonisms are involved in an increase in blood pressure at the developing stage of DOCA-salt hypertension, and that V2 agonism, but not V1 plays a major role in the maintenance of high blood pressure at the established stage.

Effects of L-arginine on impaired acetylcholine-induced and ischemic vasodilation of the forearm in patients with heart failure

BACKGROUND

Endothelium-dependent vasodilation in response to acetylcholine (ACh) and ischemic vasodilation during reactive hyperemia are attenuated in the forearm of patients with heart failure (HF). It has been shown that L-arginine augments endothelium-dependent vasodilation in healthy subjects. Thus, the aim of the present study was to determine if L-arginine improves endothelium-dependent and ischemic vasodilation in the forearm in HF.

METHODS AND RESULTS

Forearm blood flow was measured by a strain-gauge plethysmograph in 20 patients with HF and in 24 age-matched control subjects (C). Resting forearm vascular resistance (FVR) was significantly higher in HF than in C (37 +/- 4 versus 22 +/- 2 U, P < .01). Intra-arterial infusions of ACh or sodium nitroprusside (SNP) at graded doses progressively decreased FVR in HF as well as in C. The magnitude of ACh-induced vasodilation was attenuated in HF (P < .01), whereas SNP-induced vasodilation was similar between the two groups. The minimal FVR during reactive hyperemia after 10 minutes of arterial occlusion was significantly higher in HF (n = 12) than in C (n = 12) (3.2 +/- 0.4 versus 2.1 +/- 0.1 U, P < .05). L-Arginine significantly augmented maximal vasodilation evoked with ACh and decreased minimal FVR during reactive hyperemia in HF (P < .01) but not in C. L-Arginine did not affect SNP-induced vasodilation in HF or C.

CONCLUSIONS

Our results suggest that defective endothelial function may contribute to impaired ischemic vasodilator capacity in HF.

Blood pressure-lowering effect of an orally active vasopressin V1 receptor antagonist in mineralocorticoid hypertension in the rat

We studied the contribution of vasopressin to the maintenance of high blood pressure in deoxycorticosterone acetate (DOCA)-salt hypertension in the rat using the nonpeptide orally effective vasopressin V1 receptor antagonist OPC-21268. Binding kinetic studies demonstrated that oral OPC-21268 (30 mg/kg) acted as a competitive antagonist at the vasopressin V1 receptor in DOCA-salt and salt control rats. Basal mean intra-arterial blood pressure was 140 +/- 4 mm Hg (n = 12) in DOCA-salt rats compared with 111 +/- 2 mm Hg in salt control rats (n = 18). Acute oral OPC-21268 (30 mg/kg) significantly (P < .01) reduced mean intra-arterial pressure in DOCA-salt hypertension, with an average maximal decrease of 24 +/- 3 mm Hg occurring at 2.5 +/- 0.7 hours after dosing. Systolic blood pressure (tail-cuff) in DOCA-salt rats was 178 +/- 2 mm Hg. Chronic oral OPC-21268 (30 mg/kg) twice daily for 7 days significantly (P < .01) reduced systolic blood pressure in DOCA-salt hypertension, with an average maximal decrease of 27 +/- 5 mm Hg. The antihypertensive effect was reversed 5 days after treatment with OPC-21268 was stopped. In water control rats basal systolic pressure (120 +/- 1 mm Hg, n = 20) was unchanged by chronic oral OPC-21268 (30 mg/kg twice daily for 7 days), and this was confirmed by direct measurement of mean intra-arterial pressure. After chronic oral OPC-21268 (30 mg/kg twice daily for 7 days) hepatic V1 receptor binding was significantly reduced for up to 10 hours (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Human internal mammary artery responses to non-peptide vasopressin antagonists

1. OPC-21268 and OPC-31260 are newly developed orally active non-peptide vasopressin (AVP) V1 and V2 receptor antagonists, respectively. The effects of the two compounds on human vessels have not been studied. 2. The effects of the two compounds on AVP-induced contraction of human internal mammary arteries (IMA) were investigated. Their effects were compared with the peptide V1 and V2 antagonists d(CH2)5Sar7AVP (SAVP) and d(CH2)5D-Ileu2Ileu4AVP (Ileu2Ileu4AVP), respectively. 3. The V1 antagonist OPC-21268 failed to antagonize AVP-induced contraction at low concentrations and potentiated the contraction at higher concentration (3 x 10(-7) mol/L, P < 0.05). It also caused a mild direct contractile effect on IMA. In contrast, the peptide V1 antagonist SAVP potently inhibited the AVP-induced contraction, indicating that functionally constrictor V1 receptors exist in IMA. Both the nonpeptide and peptide V2 antagonists OPC-31260 (3 x 10(-6) mol/L) and Ileu2Ileu4AVP significantly antagonized the AVP-induced contraction (P < 0.01). 4. The AVP-induced contraction was reversed by high concentrations of OPC-31260 (10(-6) mol/L-3 x 10(-5) mol/L) but not by OPC-21268 (up to 3 x 10(-5) mol/L). 5. These studies indicate that, in human IMA, OPC-21268 is a partial V1 receptor agonist with no V1 receptor antagonist activity, while OPC-31260 is a V1 receptor antagonist. The results also indicate that Ileu2Ileu4AVP may be a V1 receptor antagonist in humans.

OPC-21268, a vasopressin V1 antagonist, produces hypotension in spontaneously hypertensive rats

We studied the hypotensive effects of OPC-21268, an orally effective nonpeptide vasopressin V1 receptor antagonist, in spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP). OPC-21268 was given intravenously to conscious, freely moving SHR and SHRSP. We used young and aged animals to examine the contribution of vasopressin to the development and maintenance of hypertension in both types of rats. In SHR, hypertension was fully established at 38 weeks of age, and intravenous injection of OPC-21268 produced slight hypotensive effects at either 38 or 70 weeks of age. In SHRSP, hypertension developed at 25 weeks of age, and blood pressure was sustained at a high level (approximately 250 mm Hg systolic blood pressure) thereafter. Intravenous administration of OPC-21268 did not cause hypotensive effects in young rats at 15 weeks, but at 25 weeks a significant decrease in blood pressure was observed. Furthermore, in the malignant state of SHRSP (35 to 41 weeks), OPC-21268 significantly decreased mean blood pressure by 32.4 +/- 7.9 mm Hg (mean +/- SEM) at 3 mg/kg IV, and the decrease was dose dependent (0.3 to 3.0 mg/kg). Plasma vasopressin concentrations were increased in a more malignant phase of SHRSP at 45 weeks of age, whereas at other ages of SHRSP or in SHR, plasma vasopressin levels were not increased. These results suggest that vasopressin plays an important role through V1 receptors in the maintenance of hypertension, at least in the malignant phase of SHRSP, and OPC-21268 may be therapeutically useful in the treatment of some types of hypertension.

Vasodilatory effect of arginine vasopressin is mediated by nitric oxide in human forearm vessels

Arginine vasopressin (AVP) causes biphasic changes in vascular resistance in human forearms; vasoconstriction at lower doses and vasodilation at higher doses. Vasoconstriction is mediated by the V1 receptor. However, the mechanism of AVP-induced vasodilation is not known. We investigated whether AVP-induced vasodilation is mediated by nitric oxide (NO) in human forearms by examining the effects of L-arginine (a precursor of NO) and NG-monomethyl-L-arginine (L-NMMA, a blocker of NO synthase) on AVP-induced vasodilation. AVP was infused intraarterially at doses of 0.05, 0.1, 0.2, 0.5, and 1.0 ng/kg per min (n = 8). The lower doses of AVP (< or = 0.1 ng/kg per min) increased, whereas the higher doses of AVP (> or = 0.5 ng/kg per min) decreased forearm vascular resistance (FVR) (P < 0.01). Intraarterially infused L-arginine at 10 mg/min did not alter arterial pressure, baseline FVR, or heart rate. L-arginine did not alter the magnitude of AVP-induced vasoconstriction at the lower doses, but L-arginine augmented the magnitude of AVP-induced vasodilation at doses of 0.2 (P < 0.05), 0.5 (P < 0.01), and 1.0 (P < 0.05) ng/kg per min. In another group (n = 6), intraarterially infused L-NMMA (4 mumol/min for 5 min) increased baseline FVR without systemic effects, and inhibited acetylcholine-induced vasodilation (P < 0.01). L-NMMA at this dose inhibited AVP-induced vasodilation (P < 0.01) but did not affect vasoconstriction. L-arginine reversed the inhibitory effect of L-NMMA. Our results suggest that the vasodilatory effect of AVP may be mediated by NO in human forearms.

Biochemical and pharmacological properties of SR 49059, a new, potent, nonpeptide antagonist of rat and human vasopressin V1a receptors

SR 49059, a new potent and selective orally active, nonpeptide vasopressin (AVP) antagonist has been characterized in several in vitro and in vivo models. SR 49059 showed high affinity for V1a receptors from rat liver (Ki = 1.6 +/- 0.2) and human platelets, adrenals, and myometrium (Ki ranging from 1.1 to 6.3 nM). The previously described nonpeptide V1 antagonist, OPC-21268, was almost inactive in human tissues at concentrations up to 100 microM. SR 49059 exhibited much lower affinity (two orders of magnitude or more) for AVP V2 (bovine and human), V1b (human), and oxytocin (rat and human) receptors and had no measurable affinity for a great number of other receptors. In vitro, AVP-induced contraction of rat caudal artery was competitively antagonized by SR 49059 (pA2 = 9.42). Furthermore, SR 49059 inhibited AVP-induced human platelet aggregation with an IC50 value of 3.7 +/- 0.4 nM, while OPC-21268 was inactive up to 20 microM. In vivo, SR 49059 inhibited the pressor response to exogenous AVP in pithed rats (intravenous) and in conscious normotensive rats (intravenous and per os) with a long duration of action (> 8 h at 10 mg/kg p.o). In all the biological assays used, SR 49059 was devoid of any intrinsic agonistic activity. Thus, SR 49059 is the most potent and selective nonpeptide AVP V1a antagonist described so far, with marked affinity, selectivity, and efficacy toward both animal and human receptors. With this original profile, SR 49059 constitutes a powerful tool for exploring the therapeutical usefulness of a selective V1a antagonist.

Role of AVP in the regulation of vascular tonus and blood pressure in patients with chronic renal failure

This study was undertaken to estimate the role of AVP in the regulation of vascular tonus and blood pressure, at first, during hemodialysis hypotension and, secondly, in hypertensive patients with chronic renal failure (CRF). Study 1: among 12 patients with hemodialysis (HD) hypotension showing similar metabolic and endocrine changes except plasma AVP during HD, 6 who showed an increase in plasma AVP after HD were hemodynamically examined during HD. Gradual decreases in mean BP and cardiac index, and increases in systemic vascular resistance (SVR) and plasma AVP, with a slight time-delay, were observed and thereafter BP inversely showed a slight increase at the end of HD, whereas no significant change in HR was found throughout HD. However, the % change in SVR had a positive correlation with % change in plasma AVP levels (P < 0.01, r = 0.559), but not with that in plasma renin activity or plasma norepinephrine levels. Study 2: oral administration of 100 mg of AVP.V1-receptor antagonist, OPC21268, which completely inhibited the vasoconstriction induced by the exogenously administered AVP, did not show any changes in BP and HR of seven hypertensive CRF patients. However, OPC21268 results in a marked decrease in BP of one hypertensive CRF patient with congestive heart failure (CHF) and nephrotic syndrome. Therefore, in some patients with HD hypotension showing impaired SNS and RAS, AVP may play an important role in the maintenance of BP during HD, predominantly via its peripheral vasoconstrictive action. On the other hand, AVP might not aggressively participate in hypertension of CRF patients, even with relatively high levels of plasma AVP.(ABSTRACT TRUNCATED AT 250 WORDS)