The fetal hypothalamus and pituitary during growth and differentiation

Abstract

In our project on the involvement of the fetal brain and pituitary in intrauterine growth and parturition, data on human anencephalics are compared with those obtained in experiments with rat fetuses. An intrauterine growth spurt was observed in intact rat fetuses (starting at day 19 of pregnancy) and normal human fetuses (around 20 weeks of pregnancy), which appeared to be dependent on the integrity of the fetal brain and pituitary. Rat experiments showed that the acceleration of intrauterine growth was caused by endogenous fetal α-melanocyte-stimulating hormone (α-MSH). This hormone is also shown to be present in normal human fetal pituitaries during the intrauterine growth spurt. This, together with the absence of α-MSH fluorescence in anencephalic pituitaries suggests the involvement of α-MSH also in human fetal growth. The normal course of labour appeared also to be dependent on the integrity of the fetal brain and pituitary in man and rat. Since a protracted course of labour was found in Brattleboro rats being homozygous for diabetes insipidus, the fetal hypothalamo-neurohypophyseal system was thought to stimulate the course of labour. However, using immunofluorescence techniques, that enabled the specific localization of oxytocin and vasopressin in the adult rat, these hormones were not observed in the pituitary of fetal Wistar rats near term. Instead, a cross reacting compound which was probably arginine-vasotocin (AVT) was found throughout the hypothalamo-neurohypophyseal system which, by immuno-electronmicroscopy, appeared to be localized within the neurosecretory vesicles of the fetal neurohypophysis. The presence of AVT was confirmed by radioimmunoassay. AVT was absent or only present in very small quantities in the pituitary of homozygous Brattleboro fetuses. AVT from the fetus may play a role in the course of normal delivery. The presence of AVT in the fetal rat neurohypophysis and of α-MSH in the intermediate lobe of the fetal human pituitary shows, that fetal endocrine systems might be different from those, operating in adult organisms.