Glucocorticoidal regulation of pituitary vasopressin content in rats

Although glucocorticoids are known to attenuate vasopressin (AVP) secretion , it is still controversial whether glucocorticoids act on the hypothalamo- neurohypophysial system. We report here glucocorticoidal regulation of pitu itary AVP content, which is a specific indicator for the system. The hypoth alamic AVP mRNA content and the pituitary AVP content were measured in rats given dexamethasone (2 mg/kg, 2 times over the course of 5 d) or the gluco corticoid receptor antagonist RU-38486 (20 mg/kg, 3 times over the course o f 3 d) during euhydration or dehydration. In dexamethasone-treated rats, bo th the hypothalamic AVP mRNA content and pituitary AVP content decreased af ter dehydration, In contrast, in the RU-38486 group the hypothalamic AVP mR NA content and pituitary AVP content increased in both euhydrated and dehyd rated rats, These results suggest that glucocorticoids may act on hypothala mo-neurohypophysial vasopressinergic system and attenuate its activity unde r both basal and dehydrated states.