Reduced hypotensive effect of clonidine after lesions of the nucleus tractus solitarii in rats.

Bilateral electrolytic lesion of the area of the nucleus tractus solitarii (NTS) in rats produced a sustained increase in blood pressure and reduced the hypotensive response to a single dose of clonidine (30 mug/kg, i.v.). The same dose of clonidine evoked a much larger drop in blood pressure in another group of rats in which an equialent increase in blood pressure was produced by bilateral section of the vagosympathetic trunks and occlusion of both carotid arteries. It is concluded that the dorsal part of the medulla oblongata in the area of NTS is an important link in the hypotensive action of clonidine.