[Hypothalamic factors in the human fetal brain: their role in the ontogeny of fetal hypophyseal functions].
The anterior pituitary gland of the human fetus has the ability of synthetizing, storing and secreting hormones early during gestation. The patterns of plasma concentrations of hGH, ACTH, LH and FSH during gestation indicate a maximum of secretion at mid-gestation followed by a progressive decrease of these concentrations until term. In contrast, the secretions of PRL and TSH are moderate at mid-gestation and only increase in the last trimester of gestation. Effective control by the central nervous system (CNS) of the pituitary secretions is still immature at mid-gestation. The presence of releasing factors in the fetal hypothalamus has been established (TRF, LRF, somatostatine) and it was postulated that early in life, relatively autonomous and unrestrained secretion of hypothalamic hypophysiotropic releasing factors occurs and, later in development, there was a maturation of inhibitory or restraining influences mediated via the CNS that modulate the secretion of the fetal adenohypophyseal hormones. Observations made with anencephalic newborns confirm that a functional hypothalamus is necessary for the secretions of each of the hormones of the anterior pituitary gland with the exceptiion of PRL, the secretion of which is normal in anencephaly. Although somatostatin probably participates in the regulation of hGH during fetal life, it appears evident that this regulation can only be fully understood with the existence of a GRF (Growth Hormone Releasing Factor).