Influence of exogenous ANP on the nocturnal HPA axis and sleep in healthy men

Previous studies in men demonstrated that the atrial natriuretic peptide (ANP) inhibits stimulated pituitary-adrenal secretion during wakefulness. In addition, pituitary-adrenal activity is synchronized to the sleep-wake cycle and ANP was supposed to be involved in the interaction of the HPA axis and sleep. To further characterize the role of ANP in the regulation of the hypothalamo-pituitary-adrenocortical (HPA) axis and sleep, 8 men received either an ANP infusion or normal saline at the beginning at the 1st and the 2nd half of the night in a randomized single-blinded placebo-controlled design. Sleep was assessed by polysomnography and blood samples were drawn in close intervals for determination of ACTH and cortisol. ACTH and cortisol concentrations during the ANP condition point to similar temporal profiles of both hormones with an immediate increase after infusion for 2 hours followed by an abrupt decline to placebo level. The AUC values of both ACTH and cortisol during a 2 hour interval after treatment with ANP were significantly higher than placebo, both when administered in the 1st as well as in the 2nd half of the night. Sleep-EEG parameters were not affected by ANP. While exogenously administrated ANP did not directly influence basal HPA axis, the clear-cut enhancement of ACTH and cortisol secretion indicates a rebound effect of ANP on HPA secretory activity and reinforces the view that ANP acts by inhibitory influence on the hypothalamic level.