THE ROLE OF VASOPRESSIN IN ESSENTIAL-HYPERTENSION - PLASMA-LEVELS ANDEFFECTS OF THE V-1 RECEPTOR ANTAGONIST OPC-21268 DURING DIFFERENT DIETARY-SODIUM INTAKES

To study the role of vasopressin (VP) in essential hypertension, we ex amined plasma levels of VP and blood pressure (BP) response to an oral ly active V-1 receptor antagonist, OPC-21268, in hypertensive patients on diets with different sodium contents. Plasma VP was determined in 12 normotensive subjects and 12 patients with mild essential hypertens ion on a regular sodium diet, and in eight hypertensive patients on a high sodium (250 mmol/day) and a low sodium (25 mmol/day) diet. BP res ponse was examined for 4 h after single oral administration of OPC-212 68 (100 mg) or placebo in eight patients on the regular diet, and in s ix patients on the high and low sodium diets. In four patients on the regular diet, the effects of OPC-21268 on the baroreflex control of he art rate were also examined with intravenous injections of methoxamine . Plasma VP did not differ between the normotensive and hypertensive s ubjects. Levels of VP in the plasma was higher in the high sodium than in the low sodium period, but the difference was not significant. BP and heart rate did not change significantly after administration of OP C-21268 or placebo under either condition. OPC-21268 also failed to lo wer BP in salt-sensitive patients on the high sodium diet. The barorec eptor reflex sensitivity was not modified by the administration of OPC -21268. Our results suggest that VP does not play an important role in mild essential hypertension through its action on the V-1 receptors r egardless of dietary sodium intake. (C) 1997 American Journal of Hyper tension, Ltd.