Abstract
Dipsogenic effect of α-methyl-p-tyrosine (α-MPT) was reported previousely. This study was carried out to clarify a possible mechanism for the induction of this phenomenon. The effect of α-MPT was observed in intact rats dose-relatedly. The concentration of catecholamines in the hypothalamus was diminished after α-MPT in intact rats, suggesting that the dipsogenic effect might be resulted in central action of α-MPT. However, the dipsogenic effect was found to occur in rats administered angiotensin II (A II) peripherally. The concentration of A II in peripheral blood after administration of α-MPT was significantly higher than that of control rats. Angiotensin I (A I) as well as renin was also increased in peripheral blood by α-MPT administration. Thus, α-MPT induced an activation of peripheral renin-angiotensin system. One possibility was suggested that A I would penetrate into brain, there converted to A H. The dipsogenic effect of α-MPT was enhanced by a simultaneous administration of captopril (CP) . When low dose and moderate dose of CP were pre-administrated, drinking effect of α-MPT was enhanced, whereas higher dose of CP suppressed the drinking behavior. From these experimental results, it is possible to speculate that the dipsogenic effect of α-MPT in rats may closely relate to stimulation of chemical compounds derived from reninangiotensin system in rats. Further experiment, however, will be necessary to clarify an exact mechanism for stimulation of drinking behavior due to peripheral α-MPT adminisation in rats.
