[The ontogeny of hormones of the somatotrophic axis]

The ontogenesis of the somatotropic function involving its regulatory hormones is considered from an anatomical and functional point of view. Embryogenesis of the hypothalamo-pituitary unit involving development of the hypothalamo-hypophyseal portal system is complete during early fetal life as shown in a certain number of mammalian species. The maturation of the neuroendocrine mechanisms controlling the secretion of fetal pituitary growth hormone is analyzed in the present paper. Corticosteroids may act directly on the differentiation of the somatotropic cells. During fetal life, the plasma level of GH is always higher than after birth. Despite large gaps in our knowledge, SRIF may play a prominent part in the regulation of the somatotropic function, sometimes mediating the effect of other factors, and GRF may also be active during late gestation. However, maturation is not complete until after birth especially that of somatomedins as well as the pulsatile release of GH.