title: Corticosterone-dependent driving influence of the suprachiasmatic nucleus on adrenal sensitivity to ACTH.
abstract: 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 intact 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 sham-lesioned evening controls showed an approximately 60% 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.
authors.affiliation: Interactions Fonctionnelles en Neuroendocrinologie, Institut National de la Santé et de la Recherche Médicale, Institut Fédératif Jean-Roche, Université de la Méditerranée, 13916 Marseille, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Sage
authors.forename: Daniel
authors.initials: D
authors.lastname: Maurel
authors.forename: Olivier
authors.initials: O
authors.lastname: Bosler
mesh_terms: D000311:Adrenal Glands / Q000502:physiology*; D000324:Adrenocorticotropic Hormone / Q000097:blood / Q000502:physiology*; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology; D003345:Corticosterone / Q000097:blood / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013493:Suprachiasmatic Nucleus / Q000502:physiology*
chemical_list: D005938:Glucocorticoids; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone