Ovariectomy Decreases Luteinizing Hormone-Releasing Hormone-Degrading Activities in the Anterior Pituitary in Female Mice.

Abstract

Changes in the luteinizing hormone-releasing hormone-degrading activities (LHRH-DA) in the anterior pituitary and the hypothalamus after ovariectomy (OVX) were examined in mice. Mice were decapitated at 1000 h on diestrus day 1 (D1) or on day 7, 14 and 21 after OVX. Another group of mice was also killed at 1000, 1200, 1500 and 1700 h on D1 or on day 7 after OVX to determine the change in LHRH-DA during the day. Trunk blood, the anterior pituitary and hypothalamic tissue were collected. LHRH-DA were determined by incubating the exogenous LHRH with tissue extracts at 37C for 30 min. The changes of LHRH-DA in the anterior pituitary were inversely correlated with those of LH secretion: LHRH-DA decreased after OVX when plasma LH levels increased, but did not change when plasma LH levels were kept at a stable level throughout the day on D1 or day 7 after OVX. The present results suggest that the LHRH-DA in the anterior pituitary is involved in its hypersensitivity to the LHRH stimulation after OVX.