Steroid Regulation of Luteinizing Hormone Secretion in Normal and Androgenized Rats at Different Ages1

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Abstract
Although sexual differences in the neural regulation of luteinizing hormone (LH) secretion are determined neonatally in the rat, these differences do not appear until adulthood in female rats given low doses of testosterone propionate (TP) neonatally (the delayed anovulation syndrome, DAS). To characterize this loss of the capacity for cyclic LH release, the ability of gonadal steroids to induce a surge of LH at different ages in normal, DAS (10 .mu.g TP, day 5) and anovulatory fully androgenized (FAS, 30 .mu.g TP, day 2) female rats was tested under 2 conditions. In a short-term test conducted at 30 or about 120 days of age, rats were ovariectomized at 1000 h and given 5, 1, 0.5, 0.1 or 0.05 .mu.g estradiol benzoate (EB)/100 g or oil 48 h later. Blood samples were taken 24 (1000 h), 31 (1700 h) and 55 (1700 h) h later. After 3-4 wk, these same animals were given 8, 4 or 1 .mu.g EB/100 g or oil at 1200 h and 2 mg progesterone (P) 72 h later. Blood was taken in this long-term test in 3 afternoon samples (1700 h) at 29 or 53 h after EB and 5 h after P. In the short-term test, in both normal and DAS rats, LH secretion was increased 55 h after EB injected at 32, but not at 120 days. LH secretion was not increased in FAS animals at either age. In the long-term test, conducted at approximately 60 and 150 days, normal rats showed increased LH levels 5 h after P. In DAS rats, P neither facilitated nor inhibited LH secretion at 60 days, and reduced LH release at 150 days. FAS animals showed no LH facilitation at either age. DAS rats responded normally to gonadal steroids at 30 days of age, showed a reduced LH release at 60 days, and by 150 days showed inhibition rather than facilitation of LH release. This loss of the ability of gonadal steroids to facilitate LH secretion was correlated with the development of persistent vaginal estrus in a separate group of DAS rats. It is suggested that the immediate cause of sterility in DAS rats may be the loss of the facilitatory effects of gonadal steroids on LH secretion.