Regulation of thyroid-stimulating hormone (TSH) secretion in the fetus and neonate1

A model of the development of the brain as a construct of the thyroid system.

“…Although the neuroendocrine control of thyroid hormone function develops much later in fetal development, the pituitary and hypothalamic structures begin to develop within weeks of thyroid gland emergence (22,23). The anterior pituitary gland is derived from Rathke's pouch, which first appears on gestation week 4 as an outgrowth of the primitive buccal cavity ( Figure 1, grid 2).…”

“…Cell differentiation in the pituitary is initiated by 7-8 weeks of gestation. Basophils, which include thyrotropes (thyrotropin-secreting cells) and gonadotropes (gonadotropinsecreting cells), are detected in the pituitary by 8 weeks of gestation (22), and large numbers of thyrotropes are present by 12-13 weeks of gestation (23). The development of the hypophyseal portal system, the vasculature connecting the pituitary to the median eminence, is concurrent with pituitary gland development; capillaries of the hypophyseal portal system have been detected as early as 7-8 weeks of gestation.…”

“…Fetal serum levels of TSH are first observed at 10-12 weeks of gestation. Fetal serum levels reach peak concentrations around gestation weeks 22-30, then decrease slightly until birth (22,23). The decrease in TSH before birth is thought to be, in part, in response to the onset of the negative feedback system of the maturing hypothalamic-pituitarythyroid system.…”

Plasma thyrotropin concentration in the male pig: profile from birth to puberty and the effect of season and social environment in the young adult

“…The ontogeny of the hypothalamohypophysial-thyroid axis has been studied in man, sheep and the rat (Fisher et al, 1977; Strbak and Michalickova, 1984;Roti, 1988). However, little information exists with respect to the functional development of the hypophysial-thyroid axis of the pig.…”

“…Additionally, T 4 declines between 18 and 22 wk (Marple et al, 1981) when we observed an increase in TSH. Maturational changes in other stimulatory and inhibitory factors (see Simpkins, 1982;Hershman and Pekary, 1985;Roti, 1988 for examples) known to influence TSH secretion may have contributed to the observed variations in plasma TSH, but their role(s) in the neuroendocrine regulation of TSH secretion in the pig has not been established.…”