Further studies on vasopressin-induced pressor responses to kainic acid injected into the nucleus tractus solitarii of the rat.

Kainic acid, an analogue of L-glutamate, was microinjected into the nucleus tractus solitarii of cordotomized rats. Kainic acid (30 ng) injected bilaterally into the nucleus elicited hypertension. The pressor response to kainic acid was restricted to sites in the intermediate one-third of the nucleus tractus solitarii. Plasma vasopressin levels were markedly increased during the kainic acid-induced pressor response. Intravenous injection of atropine sulphate or mecamylamine, or intraventricular injection of captopril did not affect the pressor response. It is concluded that in cordotomized rats the pressor response to kainic acid injected into the nucleus tractus solitarii is mainly mediated via increased release of vasopressin. It seems unlikely that the central cholinergic and angiotensin mechanisms are mainly responsible for the response to kainic acid.