title: Supplemental progesterone delays heat termination and the loss of progestin receptors from hypothalamic cell nuclei in female guinea pigs.
abstract: Previous studies indicate that the retention of hypothalamic nuclear progestin receptors parallels the expression of sexual receptivity in ovariectomized, hormonally treated guinea pigs. In this study, the effect of a supplemental progesterone injection on heat termination and retention of nuclear progestin receptors was examined. Ovariectomized guinea pigs were injected with 50 micrograms progesterone 48 h after receiving 4 micrograms estradiol benzoate and were tested hourly for lordosis. 8 h after progesterone treatment, animals received either 500 micrograms progesterone or the oil vehicle. The supplemental progesterone injection delayed the termination of heat by more than 2 h compared to oil-injected animals. The effect of supplemental progesterone on the retention of nuclear progestin receptors was then determined. Animals were killed 8, 10, or 14 h after the initial injection of progesterone, and cytosol and nuclear progestin receptor concentrations in mediobasal hypothalamus-preoptic area were determined. Supplemental progesterone further increased the level of nuclear progestin receptors measured at 10 h, and at 14 h these levels were still elevated above baseline. In contrast, nuclear progestin receptor levels in animals which received only the initial progesterone injection had returned to baseline by 14 h, a time when similarly treated animals were no longer receptive. These results suggest that the mechanism by which heat termination occurs may involve loss of nuclear progestin receptors.
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D004971:Estrus / Q000187:drug effects*; D005260:Female; D006168:Guinea Pigs; D007033:Hypothalamus, Middle / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D011247:Pregnancy; D011301:Preoptic Area / Q000187:drug effects* / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism / Q000494:pharmacology*; D011397:Promegestone / Q000378:metabolism; D011980:Receptors, Progesterone / Q000187:drug effects* / Q000378:metabolism; D012726:Sexual Behavior, Animal / Q000187:drug effects
chemical_list: D011980:Receptors, Progesterone; D011374:Progesterone; D011397:Promegestone