ENHANCED PRESSER RESPONSE IN SPONTANEOUSLY HYPERTENSIVE RATS INDUCED BY STIMULATION OF VASOPRESSIN-V-1 RECEPTORS

To elucidate the effect of the arginine vasopressin (AVP) system in vivo, especially V-1 and V-2 activity, on blood pressure, we measured the acute changes in blood pressure and heart rate after AVP, OPC-21268 (a V-1 receptor antagonist), and OPC-31260 (a V-2 receptor antagonist) were injected intravenously in anesthetized spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats at the age of 15 weeks. Compared with the control period, single injection of AVP 5 ng/kg significantly increased systolic blood pressure in WKY rats without a concomitant increase in heart rate, but there was no significant increase in blood pressure in SHR. In contrast, single injection of either OPC-21268 3 mg/kg or OPC-31260 3 mg/kg did not affect blood pressure or heart rate in either SHR or WKY rats. Injection of AVP after the administration of OPC-31260 induced a greater increase in blood pressure in SHR than in WKY rats, whereas injection of AVP after the administration of OPC-21268 did not induce any clear increase in blood pressure in SHR or WKY rats. These results suggest that SHR have enhanced presser activity mediated by V-1 receptors and that this increase may be due to an increase in their number. In conclusion, enhancement of V-1 activity may contribute to the development of high blood pressure in SHR.