Contractility of longitudinal smooth muscle after massive intestinal resection in rat.

To determine whether functional changes in contractility of jejunal longitudinal smooth muscle in vitro accompany the adaptive structural changes after massive intestinal resection, the investigators subjected rats either to surgical resection of 75% of the mid-jejuno-ileum or to a sham operation. The development of isometric tension in strips of jejunal tissue was measured 10, 20, 30 or 40 days after surgery. Basal stress in response to stretch was similar for both groups at all of the post-operative times. The optimal length (Lo) needed for the generation of maximal stress (130% of initial resting length) did not differ between the group that had undergone a sham operation and the group that had undergone resection. Concentration-response curves to the muscarinic agonist bethanechol had similar values for the estimated concentration at which the response is half-maximal (EC50) and maximal active stress in both groups. However, significant increases were observed in the frequency and amplitude of spontaneous and bethanechol-stimulated phasic contractions of jejunal tissues obtained from resected rats. The presence of tetrodotoxin (10(-6) mol/L) did not alter the active contractile response (tonic stress, phasic frequency and amplitude) of resected tissues. Thus, after massive intestinal resection, longitudinal smooth muscle shows no adaptive change with respect to basal or active stress but does exhibit an increase in phasic contractile activity. This altered response is non-neural; it may reflect changes in the smooth muscle itself or, alternatively, modulation of myogenic activity by prejunctional effects or by the activity of the interstitial cells of Cajal.