A possible role for the brain renin-angiotensin system in the regulation of LH secretion.

To investigate the possibility that angiotensin II (ANG II) is involved in the regulation of luteinizing hormone (LH) secretion, ANG II was injected intraventricular ANG II caused an increase in plasma LH concentrations in 10 min, whereas intravenous ANG II in the same dose had no significant effect. Intraventricular administration of the ANG II antagonist, saralasin, during the afternoon of proestrus induced a significant decrease in the number of rats ovulating and abolished the ovulatory surge in LH secretion seen in saline-injected control animals. Intravenous saralasin in two different doses failed to inhibit ovulation and produced only a small decrease in the LH surge. In animals treated with intraventricular saralasin, the increase in plasma LH concentration produced by intravenous injection of 50 ng of LH-releasing hormone (LHRH) was normal, indicating no alteration in the sensitivity of the gonadotrops to LHRH. Intraventricular administration of the converting-enzyme inhibitor, enalapril diacid, inhibited ovulation and the ovulatory surge, whereas systemically administered enalapril diacid had no effect on LH secretion. The data suggest that ANG II generated in the brain may play a significant role in the regulation of LH secretion on the day of proestrus.