Regulation of Adrenocortical Function by Vasopressin

Accumulating data obtained from various animal species indicate that vasopressin (AVP) participates in the regulation of adrenocortical function. AVP doubled aldosterone and cortisol secretion but did not affect corticosterone secretion. Pharmacological studies indicate that the AVP receptors in the cortex belong to the V1 a subtype. Activation of V1 a receptors induces breakdown of membrane phosphoinositides, with subsequent accumulation of inositol phosphates and diacylglycerol. These effects occur after receptor binding, G-protein activation and coupling to a specific phospholipase C. Inositol trisphosphate, transiently produced, induces a rapid release of Ca²⁺ from intracellular stores. Diacylglycerol activates protein kinase C, which, together with calcium, is responsible for steroid secretion. The early events of AVP action are mediated by two types of G-proteins. One is coupled to phospholipase C, and insensitive to pertussis toxin (probably G_q/₁₁) and a second one, which is inactivated by pertussis toxin (G_i protein), is involved in the stimulation of calcium influx. This Ca²⁺ influx pathway is very important, as no steroidogenic effect of AVP could be observed when experiments were performed in a calcium-free medium or in pertussis toxin-treated cells. Besides the pituitary, the adrenal is also a source for AVP production. Indeed, AVP is synthesized and secreted by chromaffin cells either present in the medulla or scattered throughout the cortex with a more prominent concentration in zona glomerulosa. AVP receptors are also present on chromaffin cells. However, in contrast to AVP receptors in the cortex, these mainly belong to the V1 b subtype, although V1 a receptors are also detected. The results summarized in this review conclusively indicate that AVP is one of the regulators of both cortex and medulla, an influence which may be mediated in part via pituitary AVP and in part via local production of AVP.

Key words

Glomerulosa Cells - Fasciculata Cells - Chromaffin Cells - Vasopressin Receptors