Effect of zaldaride maleate, an antidiarrheal compound, on visceral pain reflex induced by small intestinal distention in anesthetized rats.

Using distention of the small intestine as a visceral pain model, we investigated the effect of zaldaride maleate (ZAL), a selective inhibitor of calmodulin, on the depressor response. In pentobarbital-anesthetized rats, small intestine distention was induced by rapid application of intraluminal pressures of 40 cmH2O causing a reflex fall in arterial blood pressure. The depressor response to intestinal distention was abolished by intraperitoneal administration of capsaicin (5 mg/rat), which depletes neuropeptides such as substance P from the sensory neurons, on the mesenteric stalk and by neonatal pretreatment with capsaicin (50 mg/kg, s.c.). Morphine (20 mg/kg, s.c.) reduced the depressor response following intestinal distention. At doses of 3 mg/kg (i.v.) and higher, ZAL significantly reduced depressor response. The effect of morphine was reversed by naloxone (5 mg/kg, i.v.); the effect of ZAL was not affected. These results suggest that ZAL helps reduce the visceral pain induced by noxious stimulus and that the antinociceptive effect of ZAL is not mediated by opioid receptors.