In this review, we have attempted to discuss some of the developmental and functional aspects of the fetal hypothalamic-pituitary, pituitary-gonadal, and pituitary-adrenal axes, in both primate and non-primate species. We have considered, in particular, the influence of the fetal hypothalamus on the synthesis and secretion of growth hormone, prolactin, gonadotrophins, and adrenocorticotrophins. Our ability to determine the time of appearance of fetal pituitary hormones is limited by the sensitivity of the techniques available. The detection of specific granule-containing cell types in the fetal pituitary can be an indication of the role of the hypothalamus in pituitary differentiation. It appears that pituitary cells differentiate to a limited extent in the absence of the hypothalamus, and its presence may only be required for complete structural and functional differentiation of the gland. Growth hormone and prolactin are hormones with many sites of action in the adult but their role in fetal life has not yet been clarified. The hypothalamic control of their release is dependent on the presence of specific hypothalamic-releasing, and release-inhibiting, hormones. The localization and ontogenesis of these neurohormones has been discussed in relation to circulating levels of fetal growth hormone and prolactin. In contrast to growth hormone and prolactin, fetal gonadotrophins act on specific target organs, the gonads, and their role in the fetus has been more clearly defined. The influence of the gonadotrophins on the development of the pituitary-gonadal axis in both the male and female is discussed and we have speculated on the feedback effects of the gonads on sexual differentiation of the fetal hypothalamus. The controlling mechanisms for the synthesis and release of fetal adrenocorticotrophins is unclear. The recent identification of a family of adrenocorticotrophic peptides in the fetal pituitary may help clarify our limited understanding of the relationship between the fetal pituitary and adrenal. It is possible that these peptides are involved in the development of the fetal zone of the primate fetal adrenal and the stimulation of this gland immediately prior to parturition.
|Number of pages||33|
|Journal||Contributions to Gynecology and Obstetrics|
|Publication status||Published - 1 Jan 1979|