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In female rats neonatal treatment with oestrogen induces persistent vaginal cornification and sterility at maturity (Takewaki, 1962). Recently, we found that the pituitary secretion of prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in such oestrogenized female rats is permanently altered (Nagasawa, Yanai, Kikuyama & Mori, 1973). No data are available, however, on the effect of pituitary hormones, administered neonatally, on the secretory activity of the pituitary in adult rats. In the present experiment the pituitary secretion of prolactin, LH and FSH was measured in adult female rats treated neonatally with prolactin.
Virgin female Sprague—Dawley rats were used. Half the females in each litter were given a daily subcutaneous injection of bovine prolactin (NIH-P-B2) dissolved in 0·25–1·0 ml 0·9% NaCl solution (pH 8) for 20 days beginning on day 0 of age. The dose of prolactin was 0·5 mg for the first 5 days, 1·0 mg for the second 5
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SUMMARY
The serum and pituitary levels of prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were determined by radioimmunoassay in adult female rats treated neonatally with oestrogen and were compared with levels in normal cyclic rats at 90, 150 and/or 180 days of age. The serum level of prolactin was significantly higher and its pituitary content and concentration were lower in oestrogenized rats than in control rats at early prooestrus and on the 2nd day of dioestrus. The level of LH in the serum of oestrogenized rats was similar to the level in control rats at pro-oestrus and was higher than that of the controls at dioestrus. Pituitary levels of LH were lower in oestrogenized rats than in control rats at both pro-oestrus and dioestrus. The serum and pituitary levels of FSH in the oestrogenized rats were intermediate between the values found at dioestrus and at pro-oestrus in the controls. The results demonstrate that the pituitary of the neonatally oestrogenized female rat constantly secretes considerable amounts of these hormones.
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SUMMARY
Female Sprague—Dawley rats were fed 6-propyl-2-thiouracil (PTU) in their diet during late pregnancy and lactation. The growth and gonadal development of their pups were inhibited and in females the day of vaginal opening and onset of oestrous cycles were delayed; thyroid glands were hypertrophied. Treatment of the pups with thyroxine largely reversed these changes. The effect on body weight persisted even after treatment with PTU had stopped. At 20 days of age, the anterior pituitary glands of the pups of PTU-treated mothers contained significantly less growth hormone (GH) and prolactin than those of normal pups of both sexes. These changes persisted at 60 days of age. If the pups of PTU-treated mothers were given thyroxine from day 1 to day 20 of age, pituitary GH and prolactin content on day 20 had returned towards normal values. Thyroid deficiency was found to suppress the synthesis and release of prolactin and the synthesis of GH by the pituitary in vitro.
These findings suggest that thyroxine influenced the maturation of the pituitary directly and/or through the hypothalamus and that thyroxine deficiency in early life brought about persistent alteration of the pituitary secretion of GH and prolactin.
