Role of noradrenaline and serotonin in the central control of blood pressure in normotensive and spontaneously hypertensive rats

Abstract

Noradrenaline and alpha-methylnoradrenaline applied to the area of the nucleus tractus solitarii of the medulla oblongata decreased arterial blood pressure and heart rate of anesthetized normotensive rats. Alpha-Methylnoradrenaline was more effective than noradrenaline. Prior administration of the alpha-adrenergic blocking agent phentolamine at the same site prevented the central inhibitory action of the two catecholamines and even reversed the effect on blood pressure. The hypotensive responses evoked by electrical stimulation or alpha-methylnoradrenaline application were found to have a common distribution of the most effective site, comprising the middle-caudal part of the nucleus tractus solitarii at the obex level. Bilateral electrolytic lesions of this area caused an immediate and severe hypertension. The data suggest that the area of the nucleus tractus solitarii is a site of action of hypotensive drugs which may act by noradrenergic receptor stimulation in the brain. In addition brain serotonin may also play an inhibitory role as indicated by the association of elevated blood pressure and brainstem serotonin depletion during treatment with para-chorophenylalanine of normotensive and genetic hypertensive rats.