Antidiuretic Effects of Alpha- and Beta-Adrenoceptor Agonists Microinjected into the Hypothalamic Supraoptic Nucleus in a Water-Loaded and Ethanol-Anesthetized Rat

Abstract

Effects of catecholamines microinjected into the supraoptic nucleus in the hypothalamus on urine outflow in rats which were loaded with water and anesthetized with ethanol were studied. L-Norepinephrine, L-epinephrine and L-isoproterenol induced potent antidiuresis, showing similar time courses to each other. The ED50 values for L-norepinephrine, L-epinephrine and L-isoproterenol were approx. 25, 20 and 5 nmol, respectively. The D-isomer of isoproterenol demonstrated no significant antidiuretic activity. The effect of L-norepinephrine was inhibited strongly by preinjection of alpha- and beta-adrenoceptor antagonists. The effect of DL-isoproterenol was inhibited strongly by beta-adrenoceptor antagonists, but not affected by alpha-adrenoceptor antagonist. Among the three catecholamines, only L-epinephrine induced a tachyphylaxis in the antidiuretic effect. Visceral functions other than urine outflow such as blood pressure, respiration rate, heart rate and rectal temperature were not significantly changed by microinjecting antidiuretic doses of the catecholamines. The results demonstrated that stimulation of alpha- and beta-adrenoceptors in the supraoptic nucleus induced a potent antidiuretic effect.