Pituitary and Plasma Concentrations of Adrenocorticotrophin, Growth Hormone, Vasopressin and Oxytocin in Fetal and Maternal Sheep during the Latter Half of Gestation and the Response to Haemorrhage

Fetal haemorrhage in exteriorized fetuses of 90 to 143 days conceptual age caused marked increases in fetal plasma ACTH and AVP with maximal values for ACTH at about 40% blood loss and maximal values for AVP with somewhat smaller losses. The rates of rise of ACTH and the maximal values of ACTH were similar to those found in a non-pregnant adult female subjected to haemorrhage. Fetal plasma growth hormones rose in 2 out of 5 animals with no consistent trend in the remainder. In 2 out of 5 animals traces of oxytocin appeared. In two older fetuses in which fetal plasma corticosteroids were determined there was a moderate rise. There was no correlation between maternal and fetal plasma levels with any of the hormones. Fetal ACTH, AVP and growth hormones levels were greatly in excess of those of the mother. Fetal pituitary concentrations of ACTH, oxytocin and neurophysin at all ages were similar to those found in the adult; AVP concentrations were somewhat less. No arginine vasotocin was detected. The high hormone content of the fetal pituitary contrasted with the appearance by light microscopy in the younger animals which showed little evidence for hormone storage. The experiments indicate that the fetal pituitary in the sheep by 90 days is able to synthesize, store and increase several hormones and that haemorrhage is a potent stimulus for the release of ACTH and AVP.