[Development of hypothalamic control over thyrotropin secretion during human prenatal life]

It was shown in the tissue culture experiments that the human hypophysis secreted autonomously the thyrotrophin during the last three fourths of the prenatal life. The intensity of secretion is the highest in the end of the first third of this period, then it decreases, but during the last third it increases reliably again. During the second half of development the level of thyrotrophin in female foetuses in reliably higher than in the male ones. In the beginning of the second third of prenatal life, the hypothalamic factors decrease the autonomous thyrotrophin secretion twice in foetuses of both the sexes. In the end of the second third, sexual differences appear in their effect; they decrease reliably the autonomous thyrotrophin secretion in the male foetuses, whereas no such effect is observed in the female ones. The stimulating effect of the hypothalamic thyrotrophin releasing hormone manifests itself during the last third of prenatal life in foetuses of both the sexes. During the second half of prenatal life, the thyrotrophin concentration in blood of female foetuses is also reliably higher than in male foetuses. There is a positive correlation in female foetuses between the thyrotrophin concentration in blood and the level of hypophysial secretion under the effect of hypothalamic factors. Thyrotrophin is found in the cranial fluid of foetuses. In some cases its concentration in the cranial fluid is higher than in the blood. No correlation was found between the levels of the hormone in fluid and blood in female foetuses; a positive correlation was found in male foteuses.