Influence of capsaicin-induced denervation on neurogenic and humoral control of arterial pressure.

(1) The influence of capsaicin-sensitive afferent neurones on the regulation of blood pressure by reflex noradrenergic responses and by activation of the renin-angiotensin system was investigated in the rat anaesthetized with pentobarbital. (2) Lowering the pressure in the carotid sinus through unilateral carotid occlusion caused a reflex rise in mean systemic blood pressure which was less marked in capsaicin-pretreated rats than in controls, although an equal drop in mean pressure in the carotid sinus region was observed in both groups. Occlusion of the second carotid artery caused an additional increase in mean systemic blood pressure which was identical in the two groups. (3) Pharmacological blockade of the renin-angiotensin-system with captopril induced a more pronounced hypotonia in capsaicin-pretreated than in control rats. Yet, this difference was based on the impaired noradrenergic counterregulation in capsaicin-pretreated rats, because both groups showed identical responses to captopril following guanethidine-induced adrenergic blockade. (4) Plasma renin activity was increased by a factor of 2 following guanethidine treatment of awake animals. It reached levels 5-7 times higher than those observed in awake animals during pentobarbital anaesthesia. This anaesthesia-induced increase in plasma renin activity was not altered by guanethidine pretreatment. There was no difference in plasma renin activity between controls and capsaicin-pretreated rats under all the conditions tested. (5) These results show that the immediate reflex adjustment of blood pressure is impaired in the capsaicin-pretreated rat, possibly because of an impairment of sensors for low perfusion pressure in the carotid sinus. On the other hand, the renin-angiotension-system remains unimpaired after neonatal capsaicin-pretreatment.