Ultrastructure of the fetal rat anterior pituitary gland as term and during prolonged gestation.

The ultrastructure of the fetal rat anterior pituitary gland is described at term (day 22) and during experimentally prolonged gestation (days 23, 24, 25). The latter was achieved by daily subcutaneous injections of five mg progesterone to gravid females from the twentieth through the twenty-fourth day. Using morphological criteria for classifying pituitary cells (Moriarty, '73), six different types were observed: thyrotrophs, gonadotrophs, corticotrophs, mammotrophs, somatotrophs and non-granulated cells. During prolonged gestation (days 24 and 25 only), cells designated as corticotrophs revealed changes suggesting increased activity, i.e.,proliferation and dilation of the endoplasmic reticulum, dilated Golgi membranes and a redction of secretory granules. In addition, meconium staining , which is indicative of fetal distress, was also observed on days 24 and 25. The ultrastructural changes noted suggest an increased in corticotroph activity due to fetal hypoglycemia and hypoxia which are known to occur as a result of placental insufficiency during prolonged gestation (Roux et al., '64; Vorherr, '75; Thliveris, '76.