The sensitivity of alpha-adrenoceptors in nucleus tractus solitarii, anterior hypothalamus and hippocampus of spontaneous and renal hypertensive rats.

The responsiveness of the endogenous type II inhibitor of protein kinases to clonidine was used as an index of the reactivity of alpha 2-adrenoceptors in the brain. The stimulation of postsynaptic alpha 2-adrenoceptors by clonidine resulted in a dose-dependent decrease in type II inhibitor activity. In the nucleus tractus solitarii and anterior hypothalamus of spontaneously hypertensive rats (SHR) and renal hypertensive rats (RHR) the clonidine-induced decrease in type II inhibitor activity was markedly reduced. In contrast, clonidine was equipotent in reducing type II inhibitor activity in the hippocampus of those rats and in control normotensive animals. In addition to that, in SHR and RHR the hypothermic activity of clonidine was not reduced. Thus, it seems that in experimental hypertension the decrease of the reactivity of alpha 2-adrenoceptors occurs in the brain structures responsible for the blood pressure regulation.