Evidence that endogenous catecholamines are involved in alpha 2-adrenoceptor-mediated modulation of the aortic baroreceptor reflex in the nucleus tractus solitarii of the rat.

Microinjections of alpha-methylnoradrenaline and tyramine into the rat nucleus tractus solitarii (NTS) potentiated the depressor and bradycardiac responses to aortic nerve stimulation whereas yohimbine injected similarly inhibited them. NTS pretreatment with yohimbine inhibited the baroreflex potentiation effects of alpha-methylnoradrenaline and tyramine whereas intraventricular pretreatment with 6-hydroxydopamine inhibited only that of tyramine. These results provide evidence that endogenous catecholamines in the rat NTS are involved in alpha 2 adrenoceptor-mediated modulation of the aortic baroreceptor reflex.