Effect of glucocorticoid dexamethasone on cyclic AMP formation stimulated by pituitary adenylate cyclase-activating polypeptide (PACAP) in the cerebral cortex and hypothalamus of chick.

In this study we tested in chicks the effects of acute and chronic in vivo treatment with a glucocorticoid dexamethasone (4 mg/kg, i.p.) on PACAP-stimulated cyclic AMP formation in [3H]adenine-prelabeled slices of the hypothalamus and cerebral cortex. PACAP (1-100 nM) concentration-dependently stimulated cyclic AMP formation in both brain regions of chick. In acute experiments, dexamethasone (single dose)-injected chicks were killed after 2, 24 and 48 h; while in chronic experiment the glucocorticoid was given once daily for 12 days and the animals were killed 48 h after the last injection. The ability of PACAP to stimulate cyclic AMP formation in the hypothalamus and cerebral cortex was similar in vehicle-treated (control) and dexamethasone-treated animals, with the exception of the nucleotide response to 100 nM of the peptide in both brain regions, which was significantly larger in the group of chicks killed 48 h after the administration of the single steroid dose.