VASCULAR TONE INFLUENCES ARTERIAL-PRESSURE LABILITY AFTER SINOAORTIC DEAFFERENTATION

Sinoaortic deafferentation (SAD) results in increased variability of arterial pressure. The purpose of this study was to investigate the contribution of nonneurogenic, peripheral vasomotor mechanisms to this arterial pressure lability. In rats with SAD, ganglionic blockade combined with either captopril or a V1-vasopressin receptor antagonist reduced the high lability. Under these conditions, continuous infusions of phenylephrine and the endogenous vasoconstrictors angiotensin II, epinephrine, and vasopressin increased lability, suggesting that the level of vascular tone is important for maintaining lability. Hemodynamic changes in individual vascular beds did not correlate with pressure lability; however, the sum of the changes in resistance, an estimate of changes in total peripheral resistance, was significantly correlated. These results suggest that 1) direct actions of endogenous vasoconstrictors can induce marked variations of arterial pressure, presumably by sustaining a high background of vascular tone, and 2) variations in resistance of individual vascular beds do not account for the lability of arterial pressure evoked by infusion of vasoconstrictors. We conclude that vascular tone of neural and/or humoral origin is critical for the generation of fluctuations in arterial pressure associated with deafferentation of baroreceptors.