A novel water-soluble selective CRF 1 receptor antagonist, NBI 35965, blunts stress-induced visceral hyperalgesia and colonic motor function in rats

Abstract

The stress response involves the activation of two corticotropin-releasing factor (CRF) receptor subtypes. We investigated the role of CRF 1 in stress-related visceral responses. A novel water-soluble tricyclic CRF 1 antagonist, NBI 35965 was developed that displayed a high affinity for CRF 1 ( K i∼4 nM) while having no binding affinity to CRF 2. This antagonist also inhibited the stimulation of cAMP induced by sauvagine in CRF 1 transfected cells. NBI 35965 administered per orally (p.o.) in rats (1, 3, 10 or 30 mg/kg) inhibited dose-dependently [ 125I]sauvagine binding selectively at brain sites of CRF 1 distribution as shown by ex vivo receptor autoradiography. At the highest doses, NBI 35965 completely prevented [ 125I]sauvagine labeling in the cortex. NBI 35965 (10 mg/kg) administered p.o. or subcutaneously (sc) 1 h before intravenous CRF completely blocked the 81% shortening of distal colonic transit time induced by CRF. NBI 35965 (20 mg/kg s.c.) significantly reduced the defecation in response to water avoidance stress but not that induced by s.c. carbachol. In adult male Long-Evans rats that had undergone maternal separation, acute water avoidance stress significantly increased the visceromotor response to colorectal distention (20–80 mmHg) by 42±19% compared with the response before stress. Stress-induced visceral hyperalgesia was abolished by NBI 35965 (20 mg/kg, s.c.). The data show that NBI 35965 is a novel water-soluble selective CRF 1 antagonist with bioavailability to the brain upon peripheral administration and that CRF 1 receptor signaling pathways are involved in water avoidance stress-induced hyperalgesia to colorectal distention and stimulation of colonic transit.