CIRCADIAN AND ESTROUS CHANGES IN THE HYPOTHALAMIC PROSTAGLANDIN-E2 CONTENT AND [H-3] PROSTAGLANDIN-E2 BINDING IN FEMALE RATS

Prostaglandin E2, (PGE2) is involved in the luteinizing hormone‐releasing hormone‐stimulated luteinizing hormone surge in female rats and may act via specific membrane receptors. The following studies were performed to determine whether there were any changes in the hypothalamic PGE2 binding and/or PGE2 content which were specific to proestrus and not to the rest of the estrous cycle. Groups of female Wistar rats were sacrificed at 3‐h intervals throughout the estrous cycle to determine both the circadian and circaestral changes in the hypothalamic PGE2 content and [3H]PGE2 binding. The hypothalamic PGE2 content was maximal at 1700 h on each of the 4 consecutive days of the estrous cycle but was independent of the stage of the cycle. [3H]PGE2 binding also displayed a circadian rhythm; the lowest binding occurred near the circadian peak of PGE2, suggesting that the PGE2 binding sites were occupied by endogenous PGE2. Since such circadian rhythms were not observed in the hypothalamus of male rats, they may be under the control of ovarian steroids. Also, since PGE2 binding and the PGE2 content both exhibit a diurnal pattern independent of the day of the cycle, there may be changes in the PGE2 receptor‐mediated process coupled to an adenylyl cyclase which could explain the luteinizing hormone surge in proestrus. Copyright © 1990, Wiley Blackwell. All rights reserved