Sex and Age Differences in the Spontaneous Release of Gonadotropins from Immature Rat Pituitary Glands In Vitro

Abstract

The present study was carried out to characterize the spontaneous release of LH and FSH from the pituitary gland of infant rats in an in vitro system. In addition, the responsiveness of their pituitary glands to synthetic LHRH in vitro was examined. Wistar-Imamichi male and female rats, aged between 1 and 21 days and androgenized female rats at 7 and 21 days of age were used. One-day-old female rats were androgenized by a subcutaneous injection of 1 mg of testosterone propionate. Animals were killed by decapitation, trunk blood was collected, and the pituitary gland was dissected free and weighed. Pituitaries were placed in 9 ml-test tube with 2 ml Krebs-Henseleit solution and incubation was carried out in a shaking incubator for 6 hours at 37 degrees C under the gassing of 5% CO2 and 95% O2. After preincubation for 15 min, medium was replaced with 2 ml fresh medium and LH and FSH concentrations released during the first 3 hr-incubation period were assessed as for the spontaneous release and the second 3 hr-incubation period assessed for the response to LHRH (10(-6)M) stimulation. In an experiment, time course changes of the spontaneous release of LH and FSH were studied using 7-day-old rat pituitaries. An aliquot of 0.5 ml of medium was taken at 30, 60, 120 and 180 min during the incubation. Gonadotropin contents in the pituitaries were determined by adding the residue in the pituitary gland and the amounts released into medium. Spontaneous release of LH and FSH increased with age in both male and female rats, and the released amounts of LH as well as FSH in female rats tended to be higher than those in males at 1, 3, 7 and 21 days of age examined. But significant sex differences in the spontaneous release of LH and FSH were only seen at 21-day-old; Spontaneous release of LH in female rats was 7 times higher than that in age-matched males. Serum LH and FSH concentrations in female rats were significantly higher than those in males at all ages examined, except the LH level at 1-day-old. In contrast to LH, age and sex differences in the magnitude of the spontaneous release of FSH from the pituitary paralleled with the age and sex differences in serum FSH concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Correlative Study on Sex Differences in Pituitary Luteinizing Hormone Content and the Number of Immunoreactive Luteinizing Hormone Cells in Perinatal Rats

“…12], In the present study, pituitary LH content was sig nificantly lower in male rats as early as day 0. This is in agreement with the results of Nonaka [22]. Is the sex difference at this time related to an acute testosterone discharge that occurs 0-2 h after birth [7]?…”

“…The present study has further shown a similar high LH synthetic capacity in female neonatal pitu itary in vivo as well. The rate of hormone accumulation was greater in female rats be tween days 1 and 4, despite higher levels of LH release [5,10,14,15,24], Administra tion of testosterone propionate to female pups is known to lower pituitary LH content [13,22]. Accordingly, lack of circulating tes tosterone is most likely to be responsible for the high LH synthetic activity of the female neonatal rats.…”

“…There is now good evidence [4,13,15,17,22] that testicular androgens inhibit pituitary LH release and thus decrease serum LH in male neonatal rats to a level lower than that in female pups. Physiological evidence available suggests as well that androgens sup press not only pituitary LH release but also its synthesis [1,30].…”

“…Physiological evidence available suggests as well that androgens sup press not only pituitary LH release but also its synthesis [1,30]. Thus, most investigators [2,4,13,18,22,25,26,29] have reported that the neonatal male pituitary contains a smaller amount of LH than the female gland whether pituitary LH is expressed as concen tration or content is not important, since the pituitary' weights are similar between the sexes at least up to about 3 weeks of age [13,22]). At present, however, there is no agree ment as to the time when the sex difference at the pituitary level first becomes apparent.…”

“…There is general agreement that serum luteinizing hormone (LH) levels are higher in female rats than in male rats immediately after birth [10,14,15,24], On the contrary, considerable disagree ment exists with regard to pituitary LH lev els. Nonaka [22] found that pituitary LH con centrations are higher in female rats from the 1st through the 21st postnatal day. This sex difference has been shown on day 9 [4] or day 10 [2] in other studies.…”