T1756 CRF 2 Receptor Activation Enhances Nerve-Mediated Relaxation of the Rat Internal Anal Sphincter

Abstract

Background Corticotropin-releasing factor (CRF) and Urocortins (Ucn) are stress-related peptides. Central or peripheral administration of these peptides has been shown to increase in colonic motor activity via CRF1 receptor. We have reported that CRF1 receptor is present in the enteric nervous system (ENS) in rat colon and direct activation of CRF1 receptor in the ENS induces colonic muscle contraction without CNS pathway (Am J Physiol 2007; 293: G903-10). In contrast to CRF1 receptor, role of CRF2 receptor in the colon has not been well studied. Aim To study whether CRF2 receptor activation cause relaxation of the colonic muscle and whether CRF2 receptor is present in the ENS. Methods Internal anal sphincter (IAS) of the rat was used in this study because IAS has resting tension and its relaxation is clearly observed. IAS circular muscle strips were suspended in an organ bath and its resting tension and electrical field stimulation (EFS) -induced relaxation were examined. The effects of Ucn 2 (selective CRF2 receptor agonist) on them were studied. To study the mechanism of action of Ucn 2, we examined these effects in the presence of tetorodotoxin (TTX), CRF1 receptor antagonist antalarmin, CRF2 receptor antagonist astressin2-B, and LNAME. The localization of Ucn 2, CRF2 receptor, and NOS in the rat IAS was investigated by immunohistochemistry using confocal laser microscope.Results IASmuscle strips showed resting tension and EFS-induced relaxation in a frequency-dependent manner. Ucn 2 caused significant decrease in resting tension of IAS dose-dependently (1 nM ~ 1 μM). In the presence of TTX, astressin2-B, and L-NAME, the effect of Ucn 2 on resting tension were abolished. Ucn 2 caused significant enhancement of EFS-induced relaxation of IAS dosedependently (1 nM ~ 10 nM). L-NAME decreased the EFS-induced relaxation, and this residual relaxation was not augmented by Ucn 2. Ucn 2 and CRF2 receptor were present in the myenteric plexus of rat IAS. Ucn 2 and NOS were colocalized in some of the myenteric neuronal cells. Discussion CRF2 receptor activation caused decrease in resting tension and augmentation of EFS-induced relaxation of IAS. These mechanisms are suggested to be through nitrergic neuronal pathway. Like anxiety or depression in CNS, CRF1 and CRF2 receptors seem to act oppositely in the gut motor activity. Conclusion CRF2 receptor activation enhances nerve-mediated relaxation of the rat IAS.