Reflex control of vasopressin during hemorrhage in hypertensive rabbits

Hypertensive (HT) rabbits have impaired reflex control of heart rate and vascular tone, which is, at least in part, related to dysfunctional baroreceptors. We hypothesized that reflex control of vasopressin (AVP) would also be impaired in the HT rabbit. To test this, we compared hemorrhage-induced increases in AVP between conscious normotensive (NT) and HT rabbits. The hemorrhage-induced rise in AVP was found to be significantly (P < 0.05) attenuated in the HT rabbits. We tested a second hypothesis, that the observed impairment was related to arterial baroreceptor function, by hemorrhaging the same rabbits after reversible cardiac denervation. Under these conditions, only the arterial baroreceptors would be expected to contribute to reflex control of AVP. Impairment was still evident after cardiac denervation; that is, the hemorrhage-induced rise in AVP was significantly (P < 0.01) attenuated in the cardiac-denervated HT rabbits compared with NT rabbits. Thus impairment was, at least in part, related to arterial baroreceptors. Previously, we showed in NT rabbits that AVP only contributed to maintenance of arterial pressure (during hemorrhage), after the autonomic nervous system (ANS) had been blocked. Thus, in the present study, we compared the maintenance of arterial pressure during hemorrhage between NT and HT rabbits after ANS blockade. Blood pressure maintenance was significantly attenuated in the HT rabbits (P < 0.05). In addition, for a given fall in pressure, significantly less AVP (P < 0.05) was released in the ANS-blocked HT rabbits as compared with NT rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)