Neurohormonal control of gonadotropic secretion in primates.

With immunohistochemical techniques, products from both the parvicellular system (such as Gn-RH) and from the magnocellular system (vasopressin, oxytocin, and neurophysins) have been shown to be present in the neurons ending around the hypothalamopituitary portal capillary system. A neurosurgical technique for prolonged collection of pituitary stalk blood has been developed. Gn-RH, vasopressin, and neurophysins have been found in large amounts in pituitary stalk blood. Gn-RH levels were found to vary in a pulsatile fashion, thereby providing direct evidence for hypothalamic modulation of the discharge of LH by the pituitary. The finding of large amounts of estrogen-neurophysin in portal vein blood adds further evidence to the hypothesis that "estrogen" neurophysin may play a role in the control by the hypothalamus over the secretion of gonadotropins.