Vasopressinergic regulation of the hypothalamic-pituitary-adrenal axis: implications for stress adaptation

In addition to its role on water conservation, vasopressin (VP) regulates p ituitary ACTH secretion by potentiating the stimulatory effects of corticot ropin releasing hormone (CRH). The pituitary actions of VP are mediated by plasma membrane receptors of the V1b subtype, coupled to calcium-phospholip id signaling systems. VP is critical for adaptation of the hypothalamic-pit uitary-adrenal (HPA) axis to stress as indicated by preferential expression of VP over CRH in parvocellular neurons of the hypothalamic paraventricula r nucleus. and the upregulation of pituitary VP receptors during stress par adigms associated with corticotroph hyperresponsiveness. V1b receptor mRNA levels and coupling of the receptor to phospolipase C are stimulated by glu cocorticoids, effects which may contribute to the refractoriness of VP-stim ulated ACTH secretion to glucocorticoid feedback. The data suggest that vas opressinergic regulation of the HPA axis is critical for sustaining cortico troph responsiveness in the presence of high circulating glucocorticoid lev els during chronic stress. (C) Published by Elsevier Science B.V.