Hiromi Tsushima and Seigo Fujimoto
Department of Pharmacology, Nagoya City University Medical School, Kawasumi Mizuho-ku, Nagoya 467, Japan
Abstract: Microinjections of alpha-adrenoceptor agonists into the paraventricular nucleus (PVN) of Wistar Kyoto rats (WKY) decreased the urine outflow rate in dose- and time-dependent manners. The order of the antidiuretic potency is norepinephrine (an alpha-agonist) > phenylephrine (an alpha1-agonist) >> clonidine (an alpha2-agonist). The phenylephrine-induced effect was inhibited by WB4101 (an alpha1-antagonist), but not by yohimbine (an alpha2-antagonist). d(CH2)5-D-Tyr(Et)VAVP (a vasopressin antagonist) blocked the antidiuretic effect of phenylephrine. In spontaneously hypertensive rats (SHR), norepinephrine and phenylephrine produced weaker antidiuretic effects than in WKY. These findings suggest that the alpha1-subtype of the PVN decreases urine production mediated through vasopressin release. This mechanism is more feeble in SHR than WKY.
Keywords: alpha1-Adrenoceptor, Paraventricular nucleus, Vasopressin