Effect of in vivo administration of ZnPPIX, hemin, or granisetron alone and in combination on number of fecal pellets/3 hr. (a) ZnPPIX and hemin do not affect the number of fecal pellets/3 hr. (b) Granisetron significantly reduces this parameter although only at dose of 50 μg/Kg. (c) Preadministration of ZnPPIX increases the number of fecal pellets/3 hr in rats treated with granisetron to control levels and even higher. (d) Hemin administered before granisetron significantly decreases the number of fecal pellets/3 hr compared to basal levels at all doses of granisetron. Values are expressed as mean ± SEM of 8–12 experiments. versus their respective control.