Contractile properties of enteric smooth muscle after small bowel transplantation in rats

BACKGROUND: The effects of small bowel transplantation (SBTx) on the function of enteric smooth muscle are not understood. PURPOSE: To study the contractile properties of enteric smooth muscle after SBTx in rats. METHODS: Five groups of inbred Lewis rats (n ≥8 each group) were studied: unoperated, naive controls; operated controls 1 week (OC1) and 8 weeks after intestinal transection/reanastomosis of the proximal jejunum and distal ileum; and 1 week (TX1) and 8 weeks (TX8) after syngeneic orthotopic SBTx. Contractile activity of circular muscle strips of jejunum was evaluated in tissue chambers. Spontaneous contractile activity (force per wet weight tissue) increased in TX1, TX8, and OC1 rats (P ≤0.01). Frequency of contractions doubled in OC1 rats (P ≤0.001) but was unchanged in the other groups. In the presence of nonadrenergic noncholinergic (NANC) blockade, spontaneous contractile activity increased in TX1 and OC1 (P ≤0.005) without a change in frequency of contractions. Inhibition of neural activity with tetrodotoxoin increased amplitude and frequency in all groups. Bethanechol (3 × 10^-6 to 3 × 10^-4mol/L) increased, and norepinephrine (1 × 10^-6 to 1 × 10^-4mol/L) dose-dependently decreased the amplitude and frequency of contractions in all groups; equi-effective concentrations, however, did not differ among groups. CONCLUSIONS: The increase in contractile activity after intestinal transection/reanastomosis is secondary to an increase in frequency of contractions and not amplitude. SBTx increases contractile amplitude of circular muscle due, in part, to downregulation of NANC nerves but not via muscarinic or adrenergic hypersensitivity. These alterations in enteric physiology of intestinal contractile activity may have important implications in clinical SBTx.