Cardiac baroreflex sensitivities in conscious, unrestrained, Long Evans and Brattleboro rats.

Cardiac baroreflex sensitivity (BRS; i.e. the slope of the line relating change in pulse interval to change in systemic arterial pressure) was assessed in response to an increase in mean blood pressure (MBP) evoked by methoxamine or a decrease evoked by sodium nitroprusside. Measurements were made in Long Evans (i.e. control) and in Brattleboro (i.e. vasopressin (AVP)-deficient) rats, following acute and chronic intravascular catheterization, and in water-replete and water-deprived states (the latter designed to reduce plasma volume and activate AVP-dependent mechanisms (in Long Evans rats]. There were no differences between the corresponding values for cardiac BRS in Long Evans and Brattleboro rats. Furthermore, water deprivation caused no significant changes in cardiac BRS in either strain. These results do not support the claim that absence of endogenous AVP in Brattleboro rats is associated with marked impairment of cardiac BRS, and indicate that chronic changes in circulating AVP do not cause systematic changes in cardiac BRS.