Arginine vasopressin inhibits phasic contractions and stimulates giant contractions in monkey colon

Abdominal cramps and urgent defecation are common side effects of clinical doses of arginine vasopressin, indicating that the drug may have stimulating effects on colonic motor activity. Four strain-gauge transducers were implanted on the colon in six monkeys. A blood flow probe was fixed on the inferior mesenteric artery. After a 1-hour control recording, vasopressin, 0.13, 1.3, or 13.0 ng.kg-1.min-1, was infused intravenously for 90 minutes. The frequency of basal colonic contractions was reduced with increasing doses of vasopressin, but their mean amplitude and duration were not altered. Giant migrating contractions associated with defecation were initiated by the highest dose of vasopressin. Atropine had no effect on these giant migrating contractions but completely inhibited normal phasic contractions. Hexamethonium completely inhibited both giant migrating contractions and phasic contractions. Parasympathetic denervation of the colon did not inhibit giant migrating contractions initiated by vasopressin. Our findings suggest that the physiological concentrations of serum vasopressin present perioperatively may transiently inhibit spontaneous colon contractions but are unlikely to be the major cause of postoperative ileus. The giant migrating contractions initiated by vasopressin may account for the defecation associated with pharmacological doses of vasopressin. The initiation of giant migrating contractions by vasopressin may be mediated through a neural pathway.