Influence of progesterone on the pituitary levels of LH in the male rat.

Abstract

Effects of progesterone on pituitary gonadotrophin stores have been more extensively studied in the female than in the male rat (Rothchild, 1965). Van Rees (1959) reported that the ability of pituitary glands from male rats treated with progesterone (1 or 6 mg/day for 26 days) to stimulate ventral prostatic weights of hypophysectomized rats was lower than that of pituitary glands from controls. Ryan & Philpott (1967), however, noted variable effects of this steroid on pituitary lh stores ofcastrated rats while Kar, Kamboj & Setty (1967) observed no alterations in the pituitary 'total' gonadotrophin content (mouse uterine weight method). In view of the variable results of these workers, the pituitary lh stores of the male rat were measured in the present study by a specific assay method using a reference standard. Male rats of the Holtzman strain were housed under standardized conditions of light (14 hr of artificial illumination) and temperature (72 to 75° F), and permitted free access to Purina chow and tap water. Progesterone (Sigma Chemical Co., St. Louis) was dissolved in corn oil and injected subcutaneously at the rate of 4 mg/day in 0-2 ml oil/injection for 13 days into 45-day-old (pre¬ puberal, Experiment 1 ) rats, and for 10 days into 55-day-old (puberal, Experi¬ ment 2) rats (Table 1). At autopsy, seminal vesicles and anterior pituitary glands were weighed. The latter were pooled within each group and kept frozen. Subsequently glands were bio-assayed for lh by the ovarian ascorbic acid depletion method of Parlow (1961) employing oestrogenized assay rats (Bogdanove & Gay, 1967). The details of the assay have been described else¬ where (Labhsetwar, 1969). The results show that progesterone administration resulted in atrophy of seminal vesicles (Table 1). This was associated in both experiments with over 40% decrease in the pituitary lh stores (Table 1). These results contrast with