NTS A2a purinoceptor activation elicits hindlimb vasodilation primarily via a β-adrenergic mechanism
American Journal of Physiology. Heart and Circulatory Physiology
NTS A 2a purinoceptor activation elicits hindlimb vasodilation primarily via a ␤-adrenergic mechanism. Am J Physiol Heart Circ Physiol 278: H1775-H1782, 2000.-Previously, we have shown that activation of adenosine A 2a receptors in the subpostremal nucleus tractus solitarii (NTS) via microinjection of the selective A 2a receptor agonist CGS-21680 elicits potent, dose-dependent decreases in mean arterial pressure and preferential, marked hindlimb vasodilation. Although A 2a receptor activation
... ceptor activation does not change lumbar sympathetic nerve activity, it does markedly enhance the preganglionic adrenal sympathetic nerve activity, which will increase epinephrine release and could subsequently elicit hindlimb vasodilation via activation of ␤ 2 -adrenergic receptors. Therefore we investigated whether this hindlimb vasodilation was due to neural or humoral mechanisms. In chloralose-urethan-anesthetized male Sprague-Dawley rats, we monitored cardiovascular responses to stimulation of NTS adenosine A 2a receptors (CGS-21680, 20 pmol/50 nl) in the intact control animals; after pretreatment with propranolol (2 mg/kg iv), a ␤-adrenergic antagonist; after bilateral lumbar sympathectomy; after bilateral adrenalectomy; and after combined bilateral lumbar sympathectomy and adrenalectomy. After ␤-adrenergic blockade, stimulation of NTS adenosine A 2a receptors produced a pressor response and a hindlimb vasoconstriction. Lumbar sympathectomy reduced the vasodilation seen in the intact animals by ϳ40%, and adrenalectomy reduced it by ϳ80%. The combined sympathectomy and adrenalectomy virtually abolished the hindlimb vasodilation evoked by NTS A 2a receptor activation. We conclude that the preferential, marked hindlimb vasodilation produced by stimulation of NTS adenosine A 2a receptors is mediated by both the efferent sympathetic nerves directed to the hindlimb and the adrenal glands via primarily a ␤-adrenergic mechanism. adrenal gland; sympathetic nervous system; epinephrine; adenosine; purines; nucleus tractus solitarii The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.