Chemical stimulation of the nucleus of the solitary tract and the resulting blood pressure response.

The cardiovascular effects of catecholamines and related substances after local application into the nucleus tractus solitarii (NTS) of the medulla oblongata of urethane anesthetized rats are summarized. The catecholamines in the nanomolar dose range appear to activate stereospecifically receptor sites in the NTS, resulting in a decrease in blood pressure. Bradycardia occurs after bilateral administration of higher doses. The type of catecholaminergic receptors involved is discussed on the basis of the effects of different catecholamine receptor stimulating agents and pharmacological blockade. Both alpha-methylnoradrenaline and alpha-methyladrenaline are active and it is concluded that they both may contribute to the antihypertensive action of alpha-methyldopa. It is probable that an alpha-type of receptor mediates these hypotensive effects in the NTS. The nature of this receptor needs further characterization.