MASSIVE INTESTINAL RESECTION DEPRESSES CIRCULAR SMOOTH-MUSCLE CONTRACTILITY IN THE RAT

To determine whether functional changes in in vitro contractility and in vivo gastrointestinal transit accompany the adaptive structural cha nges seen in jejunal circular muscle after massive intestinal resectio n, rats were subjected to either surgical resection of 75% of the mid- jejunoileum or a sham operation. Basal stress in response to stretch w as similar for both groups on postoperative days 10, 20, 30, and 40. B y day 10 after surgery, tissues from resected rats exhibited a signifi cant reduction in bethanechol-stimulated tonic stress and in frequency of phasic contractions. The amplitude of spontaneous phasic activity was significantly increased; however, following cholinergic stimulatio n, the magnitude of the increase in the amplitude of phasic activity w as significantly reduced. Experiments with tetrodotoxin (10(-6) M) ind icated a myogenic origin to the reduction in bethanechol-stimulated to nic stress and the reduced frequency and altered amplitude of phasic c ontractile activity in resected animals. The tonic stress developed in response to depolarization with KCl did not differ significantly betw een sham-operated and resected rats. Transit studies showed no change in the rate of gastric emptying after resection but did reveal a signi ficant reduction in the velocity of intestinal transit. Thus, followin g massive intestinal resection the bethanechol-stimulated tonic stress response and phasic contractile activity of circular smooth muscle ar e significantly reduced, concomitant with altered intestinal transit. The reduction in contractility in the resected animals may be due to a n alteration at the level of the smooth muscle receptor and (or) its s ignal transduction pathway.