COMPARATIVE-STUDY ON DIFFERENT RESPONSES OF VASCULAR AND EXTRAVASCULAR SMOOTH MUSCLES MOUNTED INSIDE GUINEA-PIG TRACHEA - EFFECTS OF OVALBUMIN SENSITIZATION

The difference between the responses of phenylephrine (1 mu M)-precont racted vascular (endothelium-denuded rat or rabbit aortic strips) and nonvascular (rat anococcygeus muscle) smooth muscles to acetylcholine (0.1-100 mu M) was investigated when they were mounted co-axially insi de the tracheas isolated from normal or ovalbumin-sensitized guinea-pi gs. Acetylcholine produced concentration-dependent relaxations in both types of bioassay tissues. These relaxations, preciously shown to be due to the release of airway epithelium-derived relaxing factor(s), we re significantly attenuated when the epithelial layer of he tracheas w as removed mechanically (as confirmed by histological examination). Th ere were no significant differences in responsiveness to acetylcholine between vascular strips mounted inside the epithelium-intact normal o r sensitized tracheas. The phenylephrine-induced precontraction was si gnificantly more pronounced in rat anococcygeus muscles mounted inside sensitized tracheas as compared to tissues mounted inside control tra cheas. The acetylcholine-induced relaxations were significantly decrea sed but this effect disappeared when the concentration of phenylephrin e was reduced to obtain a similar precontraction level as in tissues m ounted inside control tracheas. The responsiveness of both vascular st rips and anococcygeus muscles to acetylcholine was attenuated when the y were mounted Inside sensitized tracheas and incubated with ovalbumin for 20 min, which may be explained by the epithelial damage induced b y ovalbumin challenge. This attenuation was absent when co-axial pairs , utilizing normal tracheas, were used. These results indicate a diffe rence in response patterns of the rat anococcygeus muscle and vascular strips in ovalbumin-sensitized tracheas, which should be taken into c onsideration in co-axial bioassay studies.