Effects of Yohimbine and Tolazoline on Isoproterenol and Angiotensin 2-Induced Water Intake in Rats
Subcutaneous administration of the alpha(sub 2)-adrenoreceptor antagonists, yohimbine and tolazoline, at doses up to 1000 micro-g/kg, had no effect on water intake of female rats. However, when these compounds were administered SC in combination with either the beta-adrenoreceptor agonist, isoproterenol (10 to 25 micro-g/kg, SC), or with angiotensin 2 (200 micro-g/kg, SC). water intake was enhanced. In contrast, intraventricular administration of either tolazoline (10 and 20 micro-g/kg) or yohimbine (300 micro-g/kg) failed to augment the dipsogenic response to angiotensin 2 (150 micro-g/kg, SC). Thus, the enhancing effect of these alpha(sub 2)-adrenoreceptor antagonists on isoproterenol- and angiotensin 2-induced water intakes appears to be manifested peripherally, rather than centrally. In view of the fact that clonidine, an alpha(sub 2)-adrenoreceptor agonist, has been shown to inhibit water intake induced by both isoproterenol and angiotensin 2, the results suggest that the alpha(sub 2)-adrenoreceptor may play a role in modulating water intake induced by these two dipsogenic agents.