The hypothalamic content of LH releasing factor (RF), pituitary ACTH and pituitary and plasma LH and FSH were measured by radioimmunoassay from foetal Day 15 to postnatal Day 65. Bioassayable corticotrophin releasing activity was also measured during the postnatal period. Hypothalamic LH-RF was detectable as early as foetal Day 15, increasing gradually until postnatal Day 2 and then steeply between Days 5 and 16. The levels of LH-RF were similar in both male and normal female rats until Day 41, after which the increase which had been occurring from Day 16 continued in the male but not the female. In female rats treated with testosterone propionate neonatally ('androgenized females') the hypothalamic content of LH-RF at Day 9 was significantly less than that in the male or normal female, levels reaching those found in the latter two groups by Days 16–22. The lower level of LH-RF in the androgenized female was associated with pituitary gonadotrophin and plasma FSH levels which were lower than in the normal female until Day 30. In the normal female, vaginal opening was associated with a marked drop in hypothalamic LH-RF content and in pituitary LH and FSH, but in the androgenized female, vaginal opening occurred while hypothalamic LH-RF and pituitary LH levels were still rising. The peaks in pituitary FSH and LH and in plasma LH seen on Days 22, 30 and 41, respectively, in the normal female were each delayed by 8–9 days in the androgenized female. In all three types of animal there was a significant drop in plasma FSH between Days 50 and 65 which was associated with a significant increase in pituitary FSH in the male and a significant decrease in pituitary FSH in the androgenized female rats. The day 17 foetal pituitary gland also contained ACTH, and again levels of this hormone rose steeply between Days 5 and 9. In contrast to the gonadotrophins, there was a marked divergence between the pituitary content and concentration of ACTH: content rose while concentration remained relatively steady after Day 9. There was no major difference in pituitary ACTH levels between the three types of animal throughout the study; however, around Days 16 and 50, corticotrophin releasing activity was higher in males and androgenized females compared with that in normal females.
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