Centrally induced hypotension and bradycardia after administration of alpha-methylnoradrenaline into the area of the nucleus tractus solitarii of the rat.

1 In anaesthetized rats, bilateral injections of alpha-methylnoradrenaline, noradrenaline or adrenaline into the area of the nucleus tractus solitarii (NTS) of the brain stem caused dose-dependent decreases of systemic arterial blood pressure and heart rate. The effects of alpha-methylnoradrenaline were most pronounced and lasted longest. 2 The cardiovascular effects of alpha-methylnoradrenaline appeared to be restricted to the medio-caudal part of the NTS. 3 Prior administration of the alpha-adrenoceptor blocking agent, phentolamine, reversed the fall in blood pressure and heart rate induced by alpha-methylnoradrenaline into an increase. 4 Systemic administration of atropine combined with vagotomy potentiated the inhibitory effects of alpha-methylnoradrenaline on the cardiovascular system.