Influence of Age, Prepubertal Androgen Treatment and Hypothalamic Stimulation on Adenohypophysial LH Content in Female Rats

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Abstract
Previous studies indicated that pituitary LH [luteinizing hormone] content of androgen-sterilized female rats was 1/3 less than the content of the normal proestrous gland. One explanation was that constant secretion of estrogen by the anovulatory ovary produced a constant release of LH and thus prevented storage. The present study investigated the effects of prepubertal androgen treatment on pituitary LH content prior to and after onset of puberty. Normal values obtained from 30-, 35-, 60-, and 100-day-old rats were: 3.8, 2.37, 1.22 and 1.45 [mu]g/mg. In contrast, rats which received 1.25 mg of androgen at 5 days of age had pituitary concentrations at the same ages of 0.89, 1.22, 0.75 and 0.65 [mu]/mg. Since rats sterilized with 10 [mu]g of androgen ovulate after hypothalamic stimulation without progesterone pretreatment, whereas those given the high dose of androgen do not, pituitary LH concentration was determined (at 100 days of age) and did not differ significantly from rats which received high doses of androgen (0.68 vs. 0.65 [mu]/mg). However, after hypothalamic stimulation of "low dosage" sterilized rats, the LH concentration decreased to 0.46 [mu]g/mg and ovulation occurred. In attempts to induce LH storage without progesterone pretreatment, hemiovariectomies were performed in androgen-sterilized rats. Pituitary LH assays revealed an increase in LH concentration which was comparable to that induced by progesterone (from 0.64 to 01.1 [mu]g/ mg), but hypothalamic stimulation failed to induce ovulation in the majority of animals studied. The implications of these studies regarding the primary site of action of progesterone in facilitation of ovulation in the sterile rat are discussed.