Sage, Dominique, Daniel Maurel, and Olivier Bosler. Corticosterone-dependent driving influence of the suprachiasmatic nucleus on adrenal sensitivity to ACTH. Am J Physiol Endocrinol Metab 282: E458-E465, 2002. First published October 2, 2001 10.1152/ajpendo.00287.2001.-We investigated the effects of ablation of the suprachiasmatic nucleus (SCN) on corticosterone (CORT) responses to synthetic ACTH given in either the morning or evening. After dexamethasone treatment, evening ACTH injections in

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... tact rats produced a significantly larger increase in plasma CORT compared with morning ones. In rats with SCN lesions, the ACTH-induced CORT secretion was independent of time of day, providing direct evidence for a driving influence of the SCN on the diurnal rhythm of adrenal sensitivity to ACTH. In the absence of dexamethasone treatment, the SCN-lesioned rats were selected for morning-like (ML) or evening-like (EL) basal levels of CORT. Responses to ACTH were not different in ML rats compared with sham-lesioned morning controls. In contrast, EL rats compared with shamlesioned evening controls showed an ϳ60% decrease in increment of CORT levels within the first 15 min postinjection. These results indicate that the SCN upregulates ACTH sensitivity of the adrenal cortex during the ascending phase of the daily CORT secretion and point to a critical role of glucocorticoids in determining SCN action. adrenocorticotropin hormone; hypothalamic-pituitary-adrenal axis; circadian rhythm; glucocorticoids; adrenal cortex