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

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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·mm−1) and sodium nitroprusside (SNP) (1–10 μg·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 ADinduced 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 ganglionicneurotransmission.