Regulation of hypothalamo-neurohypophysial vasopressinergic neurons by glucocorticoids

Gluco corticoids act on vasopressin (AVP) neurons in the hypothalamic-pitui tary-adrenal axis, which are responsible for ACTH secretion, in a negative feedback manner. However, it is yet uncertain whether glucocorticoids are i nvolved in the activity of vasopressinergic neurons in the hypothalamo-neur ohypophysial tract. We report here changes in pituitary AVP content specifi c for the hypothalamo-neurohypophysial system, by glucocorticoids in rats a nd humans. In rats given dexamethasone (0.5 mg, twice over 5 days) or RU-38 486 (20 mg/kg, three times over 3 days) under euhydration or dehydration, t he pituitary and the hypothalamus were used to determine AVP and AVP mRNA l evels, respectively Clinically, signal intensity of the posterior lobe dete cted by magnetic resonance imaging was compared in Gushing syndrome, Addiso n's disease, and ACTH deficiency. In dexamethasone treated rats, both level s of hypothalamic AVP mRNA and pituitary AVP decreased after dehydration. I n RU-38486 groups, both levels of hypothalamic mRNA and pituitary,AVP incre ased in euhydrated and dehydrated conditions. On the other hand, posterior lobe signal intensity was found to decrease in patients with Gushing syndro me. The results suggest that glucocorticoids act on hypothalamo-neurohypoph ysial vasopressinergic neurons to attenuate its activity under both basal a nd dehydrated states.