Differences in mediator of nonadrenergic, noncholinergic relaxation of thedistal colon between Wistar-ST and Sprague-Dawley strains of rats

Participation of nitric oxide and vasoactive intestinal peptide (VIP) in el ectrical field stimulation-induced nonadrenergic, noncholinergic (NANC) rel axation of longitudinal muscle and in balloon distension-induced descending NANC relaxation of circular muscle were studied in the distal colon of Wis tar-ST and Sprague-Dawley rats. The extent of the nitric oxide-mediated com ponent was approximately 50% in longitudinal and circular muscle of Sprague -Dawley rats, whereas this component was absent in both muscles of Wistar-S T rats. The extent of the VIP-mediated component was approximately 40% in l ongitudinal muscle of Wistar-ST rats and circular muscle of Sprague-Dawley rats, whereas this component was absent in circular muscle of Wistar-ST rat s and longitudinal muscle of Sprague-Dawley rats. In circular muscle of Spr ague-Dawley rats, in which participation of both nitric oxide and VIP in th e relaxation was suggested, inhibition of descending relaxation by N-G-nitr o-L-arginine (L-NOARG) together with VIP-(10-28) was similar to that by eit her of the antagonists, and exogenous VIP-induced relaxation was not affect ed by L-NOARG, but exogenous nitric oxide-induced relaxation was partly inh ibited by VIP-(10-28). These results suggest a linkage of the pathways medi ated by nitric oxide and VIP. In the immunohistochemical studies, nitric ox ide synthase or VIP immunoreactive neurons were seen in the ganglia, primar y internodal strands of the myenteric plexus and in the circular muscle lay er. However, the overall appearance of immunoreactive cell bodies in the my enteric plexus and the numbers of immunoreactive fibers in the circular mus cle layer appeared to be similar in Wistar-ST and Sprague-Dawley rats. Thes e results suggest that mediators of NANC relaxation in the distal colon are different in different strains of rats, i.e., Wistar-ST and Sprague-Dawley , although no such difference was seen in immunohistochemical studies. (C) 2000 Elsevier Science B.V. All rights reserved.