Mechanisms Mediating Regional Vascular Responses to Stimulation of Adenosine A 1 Receptors in the Nucleus of the Solitary Tract (NTS)

Our previous studies showed that stimulation of NTS adenosine A 1 receptors exerts variable, counteracting effects on the iliac vascular bed: activation of the adrenal medulla and β‐adrenergic vasodilation vs. vasoconstriction mediated by sympathetic nerves and vasopressin (McClure et al. Am J Physiol Heart Circ Physiol 289 : –H2542; 2005 ; FASEB 20 : , 2006). Vasopressin and β‐adrenergic receptors are differentially expressed in various vascular beds. Therefore we investigated the role of these humoral factors in NTS A 1 receptor mediated regional vascular responses. We compared the responses of iliac vs. mesenteric and renal vascular conductance (IVC, MVC and RVC, respectively) in 4 groups of chloralose/urethane anesthetized rats: intact (INT), following β‐adrenergic blockade (βX), bilateral adrenalectomy (ADX) and vasopressin V 1 receptor blockade (VX). In INT, typical biphasic responses were observed: early vasodilation (tended: IVC=RVC>MVC) followed by vasoconstriction. Both ADX and βX abolished the vasodilation (to a greater extent in βX). VX abolished/reversed iliac and mesenteric but not renal vasoconstrictor responses. We conclude that β‐adrenergic and vasopressinergic mechanisms differentially contribute to regional vascular responses evoked by stimulation of NTS adenosine A 1 receptors. NIH HL‐67814