[Ontogenesis of gonadotropic cells].

In human fetus, gonadotrophs were first detected at eight weeks of gestation. In fact, at this stage of gestation, the gonadotrophs essentially synthesize the alpha subunit of glycoprotein hormones. It is noteworthy that alpha synthesis exist during all the gestation. The profile of the secretion of LH and FSH is different according to the age and sex. It is likely that the regulation of gonadotrophs is depending on gonadoliberin (GnRH). It has been detected precociously in fetal brain, and both in vivo and in vitro studies have provided fairly convincing evidence for gonadotroph responsiveness to GnRH. The analysis of factors controlling the hypophysial differentiation was made in Rat. Gonadotrophs were first detected at 17 days of gestation in normal rat fetus. Since encephalectomy performed at 16 days of gestation did not modify the gonadotroph aspect, the organ culture method was developed to analyze these factors. In adenohypophysial primordia explanted at 11 and 12 days of gestation, GnRH 10(-9) to 10(2) M was required for the first 24 hours of culture to induce gonadotroph differentiation which was obtained in synergy with insulin and transferrin. On the other hand fetal hypothalamic GnRH and pituitary GnRH receptors were observed from 12 days of gestation. Although GnRH can be demonstrated in human fetal hypothalamus as early as 5-8 weeks of gestation, it is difficult to assess what role this peptide may have in differentiation of gonadotrophs.