V-2-RECEPTOR BLOCKADE ENHANCES PRESSOR-RESPONSE TO VASOPRESSIN - GENDER DIFFERENCE

The present study was performed to determine if the attenuated presser response to vasopressin in conscious non-estrous female rats is due i n part to an enhanced V-2-like receptor vasodilator action. In male ra ts, infusion of vasopressin at a rate of 1 ng . min(-1). kg body weigh t(-1) (wt) resulted in an increase in mean arterial blood pressure (MA BP) of about 20 mm Hg. Thirty minutes after beginning the infusion of vasopressin, the iv bolus injection of a non-peptide V-2-receptor anta gonist, OPC-31260 (2 mg . kg body wt(-1)), resulted in a further gradu al increase in MABP of approximately 8 mm Hg in the next 60 min (p < 0 .05). Thus, the presser response to vasopressin was greater in OPC-312 60-treated than in vehicle-treated male rats (p < 0.01). The presser r esponse to vasopressin 30 min after the start of its infusion was lowe r (about 8 mm Hg) in non-estrous female rats than in males. During the next 60 min of vasopressin infusion, there was a small further increa se (p < 0.05) in MABP in the females given either OPC-31260 or its sal ine vehicle. In contrast to the male rats, however, there was no diffe rence in MABP between the OPC-31260 and vehicle treated females. Thus, the present study has provided additional evidence for a V-2-like rec eptor related vasodilator effect in male rats. However, since female r ats do not appear to express a V-2-receptor mediated vasodilator respo nse, the sexually dimorphic presser response to vasopressin cannot be due to a gender difference in V-2-receptor vasodilator activity.