Behavioral insensitivity to progesterone during lactation in female rats.
Lactating female rats failed to display sexual receptivity after receiving 50 micrograms of estradiol benzoate followed by 1 mg of progesterone. Lactating rats appear to be insensitive to progesterone, based on several experiments. In ovariectomized control rats receiving moderate estrogen priming (1 microgram EB for 3 days), progesterone greatly facilitated sexual receptivity; similarly estrogen-primed lactating females showed no responsiveness to progesterone injections, even at a high dose of progesterone (10 mg). Consistent with this reduced behavioral responsiveness to progesterone, lactating females had significantly reduced nuclear progestin receptor levels after an injection of 1 mg progesterone compared to ovariectomized controls. On the other hand, both ovariectomized controls and lactating rats responded with high levels of receptivity to 3 days of priming with 10 micrograms of estradiol benzoate (without progesterone). Lactating females treated for 3 days with a moderate dose (1 microgram) of estradiol benzoate showed slightly reduced receptivity compared to ovariectomized controls; this result could reflect a reduced sensitivity to estrogen but is more likely related to the somewhat lower serum levels of estradiol and consequently lower nuclear estrogen leading to a reduced sensitivity to progesterone cannot be eliminated (since animals respond to progesterone only after estrogen priming); however, the reported results favor the idea that lactating females are primarily refractory to progesterone and do not have a generalized insensitivity to estrogen.
D000818:Animals; D001923:Brain Chemistry; D002369:Castration; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007774:Lactation; D010903:Pituitary Gland, Anterior / Q000032:analysis; D011247:Pregnancy; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D011960:Receptors, Estrogen / Q000032:analysis; D011980:Receptors, Progesterone / Q000032:analysis; D012726:Sexual Behavior, Animal / Q000187:drug effects*
D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D011374:Progesterone; D004958:Estradiol