Effect of Ovariectomy and Adrenalectomy on Luteinizing Hormone-Releasing Hormone in Pituitary Stalk Blood from Female Rats*

Abstract

The spontaneous release of LHRH has been measured in female rats subjected to ovariectomy and adrenalectomy to determine if the release of LHRH is altered in the absence of sex steroids. Release of LHRH was determined by RIA of blood collected from the cut pituitary stalk of rats anesthetized with alphaxalone-alphadolone acetate. The concentration and content of immunoreactive LHRH in pituitary stalk plasma of rats which had been ovariectomized and adrenalectomized (Ovx-Adx) for either 4 or 28 days were comparable to the levels in intact rats at the time of the proestrous surge of LH and significantly increased when compared with levels in intact diestrous rats. The increased levels of LHRH in Ovx-Adx rats were not altered by estradiol benzoate (50 μg) injected sc either 1 h before or at the beginning of the collection of portal blood. The concentration of immunoreactive LH in jugular venous plasma obtained before cutting the pituitary stalk was significantly increased in proestrous rats and in 28-day Ovx-Adx rats compared with the concentration in diestrous rats. These results indicate that LHRH can be synthesized and released in the absence of factors from the ovary or adrenal, but that one long term function of an ovarian-adrenal factor is to moderate LHRH release. It appears that in the female rat the negative feedback effect of steroid hormones is exerted, at least in part, on the LHRH release apparatus. (Endocrinology106: 363, 1980)