Antagonistic Effects of Alpha and Beta-adrenergically Coded Hypothalamic Neurones on Consummatory Behaviour in the Rat

Abstract

IN the past 5 years, we have demonstrated the diametrically opposite effects of alpha-adrenergic and beta-adrenergic amines on water balance in the albino rat. Isoproterenol, a beta-adrenergic agonist, when injected subcutaneously in single doses of 0.05–5.25 mg/kg body weight, produced in animals sated with water a copious drinking and simultaneous inhibition of the urine flow lasting about 3 h. In contrast with this paradoxical phenomenon, the administration of metaraminol, an alpha-adrenergic agonist, induced a water depleting reaction. Rats subcutaneously injected with 0.63–10.0 mg/kg body weight of metaraminol excreted large volumes of dilute urine but made no immediate efforts towards recouping this massive water loss by drinking. Both the water depleting and water sparing response could be obviated readily by treating the rats with equimolecular quantities of either alpha or beta-adrenergic blocking agents before administration of the respective agonist. These findings seemed to be consistent with the existence of central nervous system circuits of water regulation which are chemically coded to respond in antagonistic fashion to selective alpha or beta-adrenergic stimulation¹.