α-Adrenoceptor Subtype in the Hypothalamic Paraventricular Nucleus Involved in the Regulation of Urine Production: Comparison between Wistar Kyoto and Spontaneously Hypertensive Rats

Abstract

Microinjections of α-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 α-agonist)> phenylephrine (an α₁-agonist)>> clonidine (an α₂-agonist). The phenylephrine-induced effect was inhibited by WB4101 (an α₁-antagonist), but not by yohimbine (an α₂-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 α₁-subtype of the PVN decreases urine production mediated through vasopressin release. This mechanism is more feeble in SHR than WKY.