J M Stephenson

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)

Regulation of vasopressin receptors in deoxycorticosterone acetate-salt hypertension.

Since arginine vasopressin may play a role in mineralocorticoid hypertension, we examined the effects of deoxycorticosterone acetate (DOCA)-salt on vasopressin V1 and V2 receptor binding and their second messengers, inositol phosphate and adenylate cyclase, respectively, in liver and kidney to determine whether altered vasopressin receptor binding is pathogenetic in mineralocorticoid hypertension. The mean arterial blood pressure of mineralocorticoid (DOCA-salt)-treated rats (163 +/- 1 mm Hg) was increased compared with control salt-treated rats (salt) (122 +/- 1 mm Hg) and water-treated rats (120 +/- 1 mm Hg; p less than 0.001). Mineralocorticoid treatment also increased plasma sodium, osmolality, and vasopressin concentration (p less than 0.001). In the hypertensive animals, there was a reduction in hepatic V1 (DOCA-salt, 91 +/- 12; salt, 132 +/- 13; and water, 145 +/- 13 fmol/mg protein; p less than 0.05) and renal V2 receptor binding density (DOCA-salt, 53 +/- 5; salt, 93 +/- 9; and water, 95 +/- 9 fmol/mg protein; p less than 0.01), although receptor affinities remained unaltered. In contrast, the density of renal V1 receptors was increased by mineralocorticoid treatment (DOCA-salt, 24 +/- 2; salt, 16 +/- 2; water, 18 +/- 1 fmol/mg protein; p less than 0.05), although the affinity was unchanged. Downregulation of V2 receptors was associated with a decrease in maximum cyclic adenosine monophosphate levels (DOCA-salt, 19 +/- 4; salt, 49 +/- 6; water, 53 +/- 9 pmol.mg protein-1.10 min-1; p less than 0.05), whereas changes in V1 receptor levels were not associated with changes in maximum inositol phosphate levels.(ABSTRACT TRUNCATED AT 250 WORDS)

[3H]desGly-NH29-d(CH2)5[D-Ileu2,Ileu4]AVP: An AVP V2 receptor antagonist radioligand

Binding characteristics of the selective V2 antagonist radioligand [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP to rat kidney were determined. Binding was specific, saturable and reversible. The peptide bound to a single class of high-affinity binding sites with Bmax 69.4 +/- 6.8 fmol/mg protein and KD 2.8 +/- 0.3 nM. AVP and other related peptides displaced [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP binding. The order of potency of inhibition was desamino-D-AVP greater than AVP greater than d(CH2)5[D-Ileu2,Ileu4]AVP greater than oxytocin greater than d(CH2)5[Tyr(Me)2]AVP greater than d(CH2)5[sarcosine7]AVP, which is typical of a selective V2 radioligand. Autoradiographic localization of [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP binding sites in kidney showed dense binding in the inner and outer medulla with less binding in the cortex, which is consistent with known renal V2 receptor distribution.

Vasopressin and a nonpeptide antidiuretic hormone receptor antagonist (OPC-31260).

The development of nonpeptide orally active AVP analogues has provided a new tool with which to assess the physiological and pathophysiological role of vasopressin (AVP). We have previously characterised the nonpeptide vasopressin V1 receptor antagonist OPC-21268, and now report the in vitro characterisation of the nonpeptide V2 receptor antagonist OPC-31260 in the rat. OPC-31260 caused a concentration-dependent displacement of the selective AVP V2 receptor antagonist radioligand, [3H]desGly-NH2(9)[d(CH2)5, D-Ile2,Ile4]AVP from V2 receptors in rat kidney medulla membranes. The concentration of OPC-31260 that displaced 50% of specific AVP binding (IC50) was 20 +/- 2 nmol/l for renal V2 receptors. OPC-31260 also caused a concentration-dependent displacement of the selective AVP V1 receptor antagonist radioligand, [125I]-[d(CH2)5,sarcosine7]AVP from V1 receptors in both rat liver and kidney medulla membranes. The IC50 was 500 +/- 30 nmol/l for both renal and liver V1 receptors. After oral administration to rats, OPC-31260 was an effective inhibitor of AVP at renal V2 and liver V1 receptors in a time-dependent manner. In vitro binding kinetic studies showed that OPC-31260 was a competitive antagonist at both the renal V2 receptor and the hepatic V1 receptor. OPC-31260 is a nonpeptide, orally effective competitive inhibitor of AVP with a V2:V1 receptor selectivity ratio of 25:1 indicating relative V2 receptor selectivity.

EFFECTS OF AN ORALLY ACTIVE VASOPRESSIN V1 RECEPTOR ANTAGONIST

1. This paper reports on the in vitro and in vivo characteristics of a non‐peptide vasopressin V1 receptor antagonist 1‐{1‐[4‐(3‐acetylaminopropoxy)benzoyl]‐4‐piperidyl}‐3,4‐dihydro‐2(1H)‐quinolinone (OPC‐21268).

EFFECTS OF ANTI‐EMETICS ON WATER EXCRETION IN HUMANS

1. The anti‐emetic drug metoclopramide has been shown to stimulate secretion of the antidiuretic hormone arginine vasopressin. Since metoclopramide is used to treat nausea, which is another potent stimulus to vasopressin secretion, the aim of this study was to determine whether metoclopramide might limit free water excretion and so cause hyponatraemia.