The roles of alpha 2-adrenoceptors in the nucleus reticularis gigantocellularis and vagal mechanism in the cardiovascular suppressive effects of guanabenz in the rat.

In pentobarbital-anesthetized rats, pretreatment with yohimbine (10 micrograms), which was microinjected into the bilateral nucleus reticularis gigantocellularis (NRGC), significantly antagonized the reduction in arterial pressure, and the force and rate of heart contraction normally promoted by systemic administration of guanabenz (10 micrograms/kg, i.v.). At the same time, the vasodepressive as well as negative inotropic and chronotropic effects of direct application of guanabenz (500 ng) into the NRGC were attenuated by bilateral cervical vagotomy or atropine sulfate (1 mg/kg, i.v.). We conclude that guanabenz may promote antihypertension by activating the alpha 2-adrenoceptors in the NRGC, which in turn elicits cardiovascular suppression by at least facilitating the vagal outflows to the heart.