A correlative radioimmunoassay and immunohistochemical study of LHRH-induced LH depletion in the anterior pituitary of male and female neonatal rats in vitro

Abstract

After an exposure of 24 h to synthetic LHRH (100 ng/ml) in vitro, the anterior pituitaries of 4-day-old rats show a notable loss of immunoreactive material in most LH cells in males, but not in females. When radioimmunoassayed without incubation, the pituitary LH content of 4-day-old female rats is 2.8 times higher than that of males of the same age. LHRH treatment stimulates a higher rate of LH discharge in females than in males, but if LH release is expressed as a percentage of the initial pituitary LH content, there is no apparent difference. In both sexes, more than 70% of the initially stored LH is discharged into the medium after 24 h of LHRH stimulation. In males, this discharge produces a pronounced depletion, but in females, the pituitary still contains 78.2% of the initial LH content despite the large amount of hormone released. From these results, it is concluded that in newborn rats the LH synthetic rate in females is higher than that in males. This high synthetic activity, together with the large store of LH, may explain why prolonged LHRH treatment fails to cause LH depletion in females. At 4 days of age LHRH had no stimulatory effect on pituitary synthesis of LH in either sex.

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

“…In a previous report, we presented direct in vitro evidence that the neonatal female pituitary on day 4 has a higher LH synthetic activity than the male gland [29]. The present study has further shown a similar high LH synthetic capacity in female neonatal pitu itary in vivo as well.…”

“…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.…”