Development of estradiol‐induced progestin receptor immunoreactivity in the hypothalamus of female guinea pigs

Abstract

The inability of young female guinea pigs to display progesterone-facilitated lordosis has been attributed, in part, to a deficiency in the concentration of hypothalamic estradiol-induced progestin receptors, as measured by in vitro binding assays. An immunocytochemical technique was used to ascertain where, within the mediobasal hypothalamus, estradiol-induced progestin receptor levels are lower in immature than in adult females. Adult (greater than 7 weeks) and juvenile (3 weeks) ovariectomized females received 10 micrograms estradiol benzoate, a dose that primes adult, but not immature females to respond behaviorally to progesterone. Progestin receptor-immunoreactive (PR-IR) cells were counted in the arcuate nucleus (ARC) and ventrolateral hypothalamus (VLH), the two regions containing the densest populations of estradiol-induced progestin receptors in the mediobasal hypothalamus. There was no age difference in the number of PR-IR cells in the rostral or caudal VLH, but immunostaining was darker in the rostral VLH of juveniles as compared to adults. We found similar numbers of PR-IR cells in the rostral and mid-ARC, but 35% fewer immunostained cells in the caudal ARC of immature, as compared to adult females. Furthermore, staining intensity was weaker in the mid- and caudal ARC of the juvenile females. These data suggest that the ARC, not the VLH, is a site of fewer estradiol-induced progestin receptors in immature females.

Hypothalamic Estrogen Receptor‐lmmunoreactivity in Prepubertal vs Adult Female Guinea Pigs

“…Juvenile, as compared to adult. guinea pigs are also deficient in hypothalamic estradiol-induced progestin receptors ( 6,7 ), but in the ARC, not the VLH ( 9 ) . That observation, taken together with the data obtained in this experiment, is consistent with 2 hypotheses: First, it seems unlikely that the lower concentrations of estradiol-induced progestin receptors in the ARC of juveniles (as compared to adults) is a result of a similar, relative deficiency in ERs in this region.…”

“…Experiments using in vitro radioligand binding assays of tissue homogenates demonstrated lower levels of estradiol-induced progestin receptors in the mediobasal hypothalamus of ovariectomized (OVX) juvenile, as com-pared to adult females (6,7). A subsequent study, using immunocytochemistry (ICC), found fewer cells containing estradiolinduced progestin receptor-immunoreactivity in the arcuate nucleus of juveniles than in adults, but not in other regions of the mediobasal hypothalamus (9). In contrast to the lower concentrations of estradiol-induced progestin receptors found in juvenile females, no age differences in in vitro estrogen receptor binding were found in homogenates, of the mediobasal hypothalamus and preoptic area ( 5 , 7).…”

Altered expression of cytokines and sex steroid receptors in the reproductive tract of cysticercotic male mice

“…The addition of cholesterol does not reverse this effect, meaning that P450 cholesterol side chain cleavage (P450scc) may also be affected. This suggests that IL‐2 specifically affects the steroidogenic enzyme system and that there is no toxic effect of the molecule on the mouse cells (31). The mentioned effect on the steroidogenic enzyme system could be exerted by hindering steric enzyme‐substrate recognition, as IL‐2 can modify the binding site in a noncompetitive, irreversible way.…”