Degranulation of Mast Cells Due to Compound 48/80 Induces Concentration-Dependent Intestinal Contraction in Rainbow Trout (Oncorhynchus mykiss Walbaum) Ex Vivo

Rainbow trout (Oncorhynchus mykiss) intestinal strips (n=10) were mounted in an isolated organ bath and the effect of incremental doses of compound 48/80 was recorded. Compound 48/80 induced concentration-related contraction in all the examined strips following a sigmoidal dose-response curve fit. Values for maximal contraction (E-max, g cm(-2)), negative logarithm of the EC50 (pD(2)), and hill slope were, respectively (mean +/- standard error), 12.88 +/- 0.51, 1.88 +/- 0.05, 1.49 +/- 0.27. The histological modification induced on mast cells (MCs) due to compound 48/80 was characterized by mean of gray-levels and texture analysis. Significant differences were observed between gray-levels values (Linear mixed model, P<0.01), contrast, and entropy (Linear mixed model, P<0.05) of MCs from compound 48/80-treated strips compared with MCs from untreated strips. Moreover, maximal intestinal contraction (due to compound 48/80) correlates positively and significantly (Pearson and Spearman correlations, P<0.05) with degranulation intensity determined by means of gray-levels analysis. Four antisera were tested on intestinal sections and no MCs positive to serotonin, substance P, met-enkephalin, and bombesin were found. This study demonstrates that compound 48/80 induces the degranulation of trout intestinal MCs ex vivo, and that the aforementioned degranulation promotes a concentration-dependent intestinal contraction. J. Exp. Zool. 315:447-457, 2011. (C) 2011 Wiley-Liss, Inc.