Selective corticotropin-releasing factor 1 receptor antagonist E2508 reduces restraint stress-induced defecation and visceral pain in rat models

N-Cyclopropylmethyl-7-(2,6-dimethoxy-4-methoxymethylphenyl)-2-ethyl-N-(tetrahydro-2H-pyran-4-ylmethyl)pyrazolo[1,5-a]pyridin-3-amine tosylate (E2508) is a newly discovered selective corticotropin-releasing factor 1 receptor antagonist. Here, we investigated the effects of E2508 on wrap restraint stress-induced defecation and visceral pain in rats. Oral pretreatment with E2508 dose-dependently decreased stool weights after 20 min wrap restraint stress and significant effects were observed at doses of 30 and 100 mg/kg. However, E2508 did not affect basal defecation at doses up to 100 mg/kg. In contrast, alosetron, a 5-HT3 receptor antagonist, decreased both wrap restraint stress-induced and basal stool output at a dose of 0.1 mg/kg. In a rat visceral pain model, subcutaneous injections of both E2508 (0.01 and 0.1 mg/kg) and alosetron (0.001 and 0.01 mg/kg) significantly decreased the number of abdominal muscle contractions induced by colonic distention, suggesting these drugs reduced visceral pain. Together, these results demonstrate E2508 has the potential to be an effective therapy for the treatment of irritable bowel syndrome with a lower risk of adverse events such as constipation compared with the current clinically used 5-HT3 receptor antagonist.