Ovarian hormones and food intake in female guinea pigs and rhesus monkeys

Food intake was measured during ovarian cycles of female guinea pigs and rhesus monkeys. In both species, the period of lowest food intake occurred around the expected time of ovulation. Feeding levels were lowest in the guinea pig during the time of estrus, estrus being estimated on the basis of vaginal membrane changes. Minimum food intake in the rhesus occurred prior to the midpoint of the menstrual cycle, on Day 13, approximately 15–16 days before the next menstruation. In ovariectomized females of both species, either multiple or single estradiol injections significantly lowered food intake. Single progesterone injections to such females were found to have no significant effect on levels of feeding.     

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

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.     

The effect of urine from castrated male or female guinea pigs and rats on the estrous cycle of guinea pigs and rats, respectively]

A 24-hour reduced cycle duration was observed in 5-day cyclic female rats exposed to the odor of urine from male or female castrated rats. A decrease in the duration of the period of vaginal closure, ranging from 2 to 5 days, was observed in female guinea pigs exposed to the odor of urine from male or female castrated guinea pigs. The pheromonal activity of urine in both species was concluded to be no dependent upon the gonadal function.     

Effects of neonatal estrogen treatment of female guinea pigs on mounting behavior in adulthood

Female guinea pigs were treated with 200 micrograms estradiol dipropionate (ED) daily from Days 1 to 15 of life. As adults they all ovulated. After gonadectomy and estrogen-progesterone treatment in adulthood, lordosis behavior was evident and showed no decrements (compared with neonatally oil-treated controls) except for a marginal decrease in maximum duration scores. However, testosterone propionate treatment in adulthood significantly increased mounting behavior in neonatally ED-treated females compared to the controls. On the other hand, estrogen-progesterone treatment in adulthood stimulated mounting in the neonatally oil-treated group, but not in the neonatally estrogenized group. The results suggest that at least some aspects of steroid-dependent behaviors can be permanently influenced by estrogen treatment after the presumed prenatal critical period for sexual differentiation has been completed in guinea pigs.     

Inhibitory actions of progesterone on hormonal induction of estrus in female guinea pigs.

Biphasic actions of progesterone (P) were studied in three groups of guinea pigs injected with 3 μg estradiol benzoate (EB) followed 36 hr later with either .05, 0.4, or 5.0 mg P. All animals in each group displayed estrous behavior within 5–7 hr after P. Groups differed, however, in their response to a second sequence of 3 μg EB and 0.4 mg P initiated 9 hr after the first or prior P. Percentages of females displaying estrous responses were 100, 50, and 0 in the .05, 0.4, and 5.0 mg groups, respectively.Radioimmunoassay of P at varying times after the first or prior injection showed that concentrations in the plasma declined to baseline within 9–18 hr for animals given prior injections of .05 mg P, within 36 hr for those given 0.4 mg P, and remained elevated throughout for 45 or more hr for those given 5.0 mg P.A second experiment showed that the inhibitory effect of 1.0 mg P given to spayed females without prior estrogenization (direct inhibition) was inversely related to the time elapsing between that injection and the initiation of a sequential regimen consisting of 6 μg EB and 0.4 mg P, and also demonstrated that 0.05, 0.1, 0.25, 0.5, or 1.0 mg P given 2 hr before the sequential regimen results in a dose-related inhibition. Thus, prior facilitation of lordosis is in no way essential for inhibition with exogenous P, and variables that regulate degree of biphasic inhibition also regulate direct inhibition.