Prolonged orexin administration stimulates steroid-hormone secretion, acting directly on the rat adrenal gland

Orexins A and B are two hypothalamic peptides, that play a role in the cent ral control of food intake. Orexins act via two subtypes of receptors: OX1R which is selective for orexin A, and OX2R which binds both orexins. Revers e transcription-polymerase chain reaction demonstrated the expression of bo th OX1R and OX2R gene in the adrenal cortex of adult female rats. The prolo nged systemic administration of orexins A and B (20 ng/kg.day, for 7 days) affected neither adrenal weight and the morphology of adrenocortical zones (as evaluated by morphometric techniques) nor ACTH plasma concentration in rats. In contrast, the treatment with both orexins increased plasma concent ration of both aldosterone and corticosterone. Taken together, these findin gs indicate that orexins exert a marked direct chronic secretagogue action on adrenocortical cells, acting through both OX1R and OX2R.