Rat spontaneous basal duodenal activity after ZnPPIX, hemin, or granisetron alone and in combination. (a) ZnPPIX (60 min, 10 μM), an HO-inhibitor, and hemin (120 min, 10 μM), an HO-1 inducer, significantly increase, the number of cycles/15 sec. Granisetron does not affect this parameter. When coadministered, granisetron abolishes ZnPPIX effects but does not influence hemin effect. (b) ZnPPIX significantly reduces mean amplitude. This parameter was not affected by either hemin or granisetron. When coadministered, granisetron abolishes ZnPPIX effect but does not modify the lacking effect of hemin. Values are expressed as mean ± SEM of 8–12 experiments. versus their respective control.