Pre-and Postganglionic Sympathetic Nerve Activity during Induced Hypotension with Adenosine or Sodium Nitroprusside in the Anesthetized Rat

Abstract

The aim of this study was to examine the effects of adenosine (AD)-induced hypotension on preganglionic adrenal (aSNA) and postganglionic renal (rSNA) sympathetic nerve activity. rSNA (n = 10) and aSNA (n = 6) were recorded together with mean arterial pressure (MAP) and heart rate (HR) in chloralose-anesthetized, artificially ventilated rats. In each experiment, hypotension was induced by equihypotensive doses of AD (0.03-2.0 mg.kg-1.min-1) and sodium nitroprusside (SNP) (1-10 micrograms.kg-1.min-1). SNP induced a progressive reflex tachycardia and a reflex increase in rSNA to levels 159 +/- 35% above control at a MAP reduction of 55% of the normotensive control value. Equipotent doses of AD induced a decrease in HR and significantly less pronounced reflex increase in rSNA. The maximal increase in rSNA with AD was 55 +/- 19% at a MAP reduction of 30%. At higher infusions rates of AD, rSNA progressively declined toward the normotensive control values. However, AD elicited a progressive increase in preganglionic aSNA that was not significantly different from the increase seen during SNP infusion. It is concluded that AD-induced hypotension is associated with a suppression of postganglionic sympathetic nerve activity caused by an inhibition of ganglionic neurotransmission.