%0 Journal Article %A Akira Ito %A Saul M. Schanberg %T MAINTENANCE OF TONIC VASOMOTOR ACTIVITY BY ALPHA AND BETA ADRENERGIC MECHANISMS IN MEDULLARY CARDIOVASCULAR CENTERS %D 1974 %J Journal of Pharmacology and Experimental Therapeutics %P 392-404 %V 189 %N 2 %X A dose-related decrease in blood pressure and heart rate occurred in vagotomized rats after intracisternal (i.e.) injection of phentolamine, an alpha adrenergic antagonist. The site of action of these effects was determined to be localized to the central nervous system. The depressor response was reversed by alpha adrenergic agonist, norepinephrine or phenylephrine, and augmented by the beta adrenergic agonist, isoproterenol. These agonists, however, had no effect on the phentolamine-induced bradycardia. Phenoxybenzamine, an irreversible alpha adrenergic antagonist, administered i.e. also caused a decrease in blood pressure and heart rate but these effects were not reversed by norepinephrine. The i.e. injection of norepinephrine without antagonist pretreatment caused a transient increase in blood pressure while isoproterenol caused a decrease. A beta adrenergic antagonist, propranolol, administered i.e. caused a pressor response in small doses and a depressor response in large doses but only a dose-related decrease in heart rate. The propranolol-induced pressor response was reversed by isoproterenol and enhanced by norepinephrine. Data from sequential transections of the brain stem and from direct application of phenylephrine, norepinephrine or isoproterenol on the brain stem surface after transections suggest that the pressor response elicited by alpha adrenergic agonists originates in a region of the medulla localized between the inferior cerebellar peduncle and the caudal end of the obex. The beta adrenergic depressor response, however, appears less localized and to originate from a more diffuse region. These results suggest that alpha adrenergic pressor and beta adrenergic depressor mechanisms are involved reciprocally in tonic blood pressure control mechanisms located in the medulla oblongata of rats. Although the i.e. administration of phentolamine or propranolol also depresses heart rate, the data do not suggest a simple adrenergic mechanism. These studies show clearly that receptor mechanisms for heart rate control in the central nervous system are different from those involved in the regulation of blood pressure. © 1974 by The Williams & Wilkins Co. %U https://jpet.aspetjournals.org/content/jpet/189/2/392.full.pdf