Antihypertensive effect of vasopressin withdrawal in young and adult spontaneously hypertensive rats.

Abstract

The extent to which age influences the effect of prolonged intravenous infusion and withdrawal of arginine vasopressin (AVP) on blood pressure was investigated in spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto controls (WKY) of 6-, 10-, 14-, 18-, and 22-week age groups. The pressor response to AVP (20 ng/kg/min for 3 hours) was relatively well maintained in WKY but showed an age-dependent tachyphylaxis in SHR. After cessation of the infusion, arterial pressure of SHR fell in all age groups. In contrast, withdrawal of AVP in WKY resulted in little or no hypotensive response. Thus, a withdrawal-induced antihypertensive phenomenon (WAP) to AVP was specific to SHR. The magnitude of the WAP was significantly correlated with the level of initial blood pressure in SHR (r = -0.81, p less than 0.001). The magnitude of the tachyphylaxis during the AVP infusion was also correlated with the level of initial blood pressure in SHR (r = -0.66, p less than 0.001). Accordingly, a significant correlation was found between the magnitude of the WAP and the degree of tachyphylaxis to the pressor activity of AVP in SHR (r = 0.69, p less than 0.001). The significance of this is unknown, but it might mean that a common underlying mechanism existed in the expression of the tachyphylactic phenomenon and the WAP in SHR. Finally, an apparent enhancement in the baroreceptor reflex sensitivity was observed in both SHR and WKY during the infusion of AVP, but the magnitude of this enhancement appeared to be greater in SHR than in WKY.(ABSTRACT TRUNCATED AT 250 WORDS)