Development of Fetal Thyroid System Control
The hypothalamic-pituitary-thyroid system in the fetus is comprised of a complex of hypothalamic centers, anterior pituitary thyrotroph cells, thyroid follicular cells, and peripheral tissues which metabolize and respond to thyroid hormones. Embryogenesis of the hypothalamus and of the pituitary and thyroid glands is largely completed by 12 weeks of gestation in the human fetus. Hypothalamic histogenesis and differentiation and continued growth and functional maturation of the pituitary and thyroid glands proceed into the neonatal period (1). Studies of thyroid system maturation have been conducted in many species, but most detailed data have been developed in the sheep and rat models. The period of thyroid system development in man, a precocial species, extends to one month of postnatal life (some 44 weeks). In the sheep (also a precocial species), comparable thyroid system maturation encompasses 150 days of intrauterine gestation plus two weeks of postnatal life (165 days total). In the rat (an altricial species) thyroid system development requires some 50 days (21 fetal days + 28 postnatal days). Relative thyroid system maturation in these species is quite comparable and thyroid control matures during the latter half of the period of ontogenesis. Thus, the third trimester fetal sheep and neonatal lamb and the neonatal rat have served as useful models for the study of thyroid control maturation. The following discussion of the development of various aspects of control of thyroid hormone production will review data in the three species normalized as relative development time to facilitate species comparisons.
KeywordsThyrotropin Release Hormone Human Fetus Thyroid Hormone Secretion Thyroid System Neonatal Lamb
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- 1.Fisher, D.A., Dussault, J.H., Sack, J. and Chopra, I.J. (1977) Ontogenesis of hypothalamic-pituitary-thyroid function and metabolism in man, sheep, and rat. Rec Prog Horm Res 33: 59Google Scholar
- 6.Kaplan, M.M. (1983) Metabolism of thyroid hormones. In: Congenital Hypothyroidism ( Dussault JH and Walker P, Eds), Marcel Dekker Inc., New York, pp 11 – 35Google Scholar
- 14.Coulombe, P., Ruel, J., Favre, R. and Dusssault, J.H. (1983) Pituitary nuclear triiodothyronine receptors during development in the rat. Am J Physiol: Endocrinol Metab 8: E81Google Scholar
- 16.Castaign, H., Fournet, J.P., Leger, F.A., Keisgen, F., Piette, C., Dupard, M.C. and Savoie, J.C. (1979) Thyroid of the newborn and postnatal iodine overload. Arch Fr Pediatr 36: 356Google Scholar
- 20.Polk, D.H., Reviczky, A.L., Lam, R.W. and Fisher, D.A. (1988) Thyrotropin releasing hormone: effect of thyroid status on tissue concentrations in fetal sheep. Clin Res 36: 203AGoogle Scholar
- 29.Frankel, S. and Lange, G. (1980) Maturation of hypothalamic-pituitary thyroid response in the rat to acute cold. Am J Physiol (Endocrinol Metab)2: E223Google Scholar
- 30.Theodoropoulos, T., Braverman, L.E. and Vagenakis, A.G. (1979) Circulating immunoreactive TRH in the neonatal rat. Dissociation between TRH release and TSH response following cold exposure. Endocrine Soc., Abstr. 427Google Scholar
- 39.Perelman, A.H., Klein, A.H. and Fisher, D.A.: Cord blood thyrotropin releasing hormone. Clin Res. 29:111A (Abstract).Google Scholar