Contractile activity of circular smooth muscle in rats one year after small bowel transplantation: differing adaptive response of the jejunum and ileum to denervation.

The aim of the present study was to determine the long-term effects of isogeneic small bowel transplantation (SBT) on jejunal and ileal circular smooth muscle contractile activity in the rat. Transmural strips of circular muscle were prepared from proximal jejunum and distal ileum of 1-year-old control rats and rats 1 year after SBT (SBT-1Y) to measure isometric force. Spontaneous contractile activity and the dose-responses to bethanechol and norepinephrine were studied. Electrical field stimulation (EFS) at varying frequencies (1 to 20 Hz) was evaluated under adrenergic and cholinergic blockade to investigate inhibitory nerves. Spontaneous activity both in the jejunum and ileum in SBT-1Y rats was not different compared to control rats. Sensitivity to bethanechol did not differ between control and SBT-1Y rats in the jejunum or ileum. Sensitivity to norepinephrine, however, was significantly increased after SBT in the ileum but not in the jejunum. During EFS, inhibition was seen at low frequencies, and contractions were induced at high frequencies in all groups. The degree of inhibition did not differ between control and SBT-1Y rats in the jejunum; however, it tended to be increased in the ileum after SBT. The long-term adaptive response of smooth muscle to the extrinsic denervation accompanying SBT differs between the jejunum and the ileum.