Endocrinology, Vol 98, 295-304, Copyright © 1976 by Endocrine Society

ARTICLES

Pituitary-thyroid axis in neonatal and adult rats: comparison of the sexes

JD Kieffer, H Mover, P Federico and F Maloof

Systematic comparisons have been made of the development of the pituitary-thyroid axes of male and female rats, by measuring plasma thyrotropin (TSH) and thyroxine (T4) concentrations in neonates and adults. Observations were made in untreated groups as well as in rats treated with various regimens of exogenous T4, thyrotropin-releasing hormone, or TSH. All hormone determinations were by radioimmunoassay (RIA). Salient findings include the following: 1) In early neonatal life, untreated rats showed no significant sex difference in the plasma concentrations of either TSH or T4. 2) In adulthood, the plasma TSH of untreated males attained levels strikingly higher than those of neonates-the differences averaged 5-fold more. For females, the increase in plasma TSH during development was less marked, averaging slightly less than 2-fold more. Thus, untreated adults exhibited a clear sex difference in circulating TSH concentrations; the male TSH levels averaged 2.8-fold higher than those of females. 3) Plasma T4 concentrations also increased markedly during development. For both sexes, adult T4 levels were approximately 3-fold greater than the T4 levels in early neonatal life. Among untreated adults, the female T4 concentrations averaged 28% greater than those of males. 4) Plasma TSH and T4 concentrations exhibited only minor fluctuations, of borderline statistical significance, during the female estrous cycle. 5) A significant reduction in responsiveness to exogenous TRH was observed in adult male rats which had been treated with high doses of T4 in neonatal life, although the effect was not completely consistent. No significant reduction was observed in females which received the same treatment. We have concluded that major changes occur in the circulating hormone levels of the pituitary-thyroid axis of the rat between birth and adulthood, and that such changes are not identical for the two sexes.

This article has been cited by other articles:

				T. E. Stoker, S. C. Laws, K. M. Crofton, J. M. Hedge, J. M. Ferrell, and R. L. Cooper Assessment of DE-71, a Commercial Polybrominated Diphenyl Ether (PBDE) Mixture, in the EDSP Male and Female Pubertal Protocols Toxicol. Sci., March 1, 2004; 78(1): 144 - 155. [Abstract] [Full Text] [PDF]

				N. Fujimoto, H. Onodera, K. Mitsumori, T. Tamura, S. Maruyama, and A. Ito Changes in thyroid function during development of thyroid hyperplasia induced by kojic acid in F344 rats Carcinogenesis, August 1, 1999; 20(8): 1567 - 1572. [Abstract] [Full Text] [PDF]

				T Theodoropoulos, L. Braverman, and A. Vagenakis Iodide-induced hypothyroidism: a potential hazard during perinatal life Science, August 3, 1979; 205(4405): 502 - 503. [Abstract] [PDF]

				J. Neary, J. Kieffer, P Federico, H Mover, F Maloof, and M Soodak Thyrotropin releasing hormone: development of inactivation system during maturation of the rat Science, July 30, 1976; 193(4251): 403 - 405. [Abstract] [PDF]