Vasopressin and Adrenal Cortical Interactions

Abstract

This chapter describes the application of immunohistochemical techniques, which has revealed a vasopressin pathway to the zona externa that arises from the paraventricular nucleus and is separate from the one to the posterior pituitary. The chapter also discusses a similar corticotropin-releasing factor (CRF) pathway, which is apparently different from that containing vasopressin. It has been established, by immunohistochemical techniques, that there is a vasopressin neurosecretory system that originates in the paraventricular nucleus and terminates on the hypophysial portal system. It appears to be a separate pathway from the magnocellular projection to the posterior pituitary gland. Release of vasopressin into the portal blood in concentrations high enough to participate in ACTH release may arise from the secretory terminals. Glucocorticoid deficiency has been found to be associated with the increase in RNA turnover in paraventricular nucleus vasopressin neurons, in vasopressin biosynthesis, and in the content of vasopressin in the cell bodies. The marked increase in the numbers of vasopressin terminals in the zona externa of the median eminence between days 5 and 21 following adrenalectomy is not due to the sprouting of pre-existing terminals. However, sprouting occurs in response to a unilateral lesion of the paraventricular nucleus in adrenalectornized animals. Within three weeks, vasopressin fibres from the intact side reinnervate the denervated side of the zona externa. These results suggest a complex interaction between this vasopressin neurosecretory system and adrenal glucocorticoid levels.