Antidiuretic effects of alpha- and beta-adrenoceptor agonists microinjected into the hypothalamic paraventricular nucleus in a water-loaded and ethanol-anesthetized rat

Abstract

Effects of catecholamines microinjected into the paraventricular nucleus in the hypothalamus on urine outflow in a rat which was loaded with water and anesthetized with ethanol were studied. L-Norepinephrine, L-epinephrine and L-isoproterenol induced potent antidiuresis with similar time courses to each other. The ED50 values for L-norepinephrine, L-epinephrine and L-isoproterenol were approximately 5, 10 and 5 nmol, respectively. The D-isomer of isoproterenol demonstrated no significant antidiuretic activity. The effect of L-norepinephrine was inhibited strongly by premicroinjection 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. Premicroinjection of a muscarinic antagonist, atropine, partially inhibited anti-diuretic effects induced by L-norepinephrine and DL-isoproterenol. Visceral functions other than urine outflow such as mean blood pressure, respiration rate, heart rate and rectal temperature were not significantly altered when the urine outflow decreased down to 20-30% of the control by microinjection of L-norepinephrine and DL-isoproterenol. The results demonstrated that stimulation of alpha- and beta-adrenoceptor in the paraventricular nucleus induced potent antidiuretic effects, partial inhibition of which by atropine suggested a possible presynaptic facilitation of the release of ACh by the stimulation of the adrenoceptors.