Corticotropin releasing factor receptor-mediated stimulation of adenylate cyclase activity in the rat brain

Abstract

Corticotropin releasing factor (CRF)-stimulated adenylate cyclase activity and receptor binding were examined in the rat brain homogenates using a potent synthetic CRF analog—[ d-Tyr 3, d-Pro 4, Nle 18,21, α-helical]CRF 3–41 (α-hel CRF 3–41). Binding of α-hel CRF 3–41 in the rat brain was saturable, reversible, of high affinity and exhibited relevant peptide specificity. This analog also stimulated adenylate cyclase activity of various brain regions; the greatest magnitude of stimulation was in the cerebral cortex followed by the septum, cerebellum and thalamus. Adenylate cyclase stimulation in the cerebral cortex was concentration-dependent with an ED 50 of2.5±0.4nM for α-hel CRF 3–41 and an ED 50 of16 ± 2nM for ovine and rat CRF. Maximal stimulation was comparable for all peptides. Agonist-stimulated adenylate cyclase activity was competitively blocked by the CRF antagonists. The inactive CRF analog, ovine CRF 1–39, at concentrations less than 1μM, did not significantly stimulate adenylate cyclase. Adrenalectomy, which has been reported to modulate CRF receptor number and CRF-stimulated adenylate cyclase activity in the anterior pituitary, had no effect on CRF receptor binding or CRF-stimulated adenylate cyclase activity in the cerebral cortex. These results suggest that, as in the anterior pituitary, at least some of the physiological responses mediated by CRF receptors in the brain utilize the cyclic nucleotide regulatory pathway as a post-receptor mechanism.