24: Effect of extrinsic denervation on NANC innervation with substance P and VIP in longitudinal smooth muscle of the rat jejunum

Abstract

Obligate extrinsic denervation may contribute to enteric motor dysfunction of the transplanted gut. We showed that chronic extrinsic denervation decreased response to exogenous Substance P (Sub P) and abdominal operations transiently increased sensitivity to exogenous Vasoactive intestinal polypeptide (VIP) (Neurogastroenterol Motil 18:779, 2006). Aim: To determine effects of extrinsic denervation mediated by endogenous release of the nonadrenergic, noncholinergic (NANC) neurotransmitters Sub P and VIP. Methods: Jejunal longitudinal muscle strips were obtained from 3 groups of Lewis rats (n ≥ 6/group): NC (naive controls); 8 wks after jejunal and ileal transaction/anastomosis to disrupt enteric myoneuronal continuity (T/A-8), and after syngeneic (no immune rejection) jejunoileal transplantation (SBT-8). Endogenously released Sub P and VIP were studied using electrical field stimulation (EFS; voltage 10V, pulse width 0.5msec, duration 10sec) at 50Hz (excitatory) and 6Hz (inhibitory) frequencies under NANC-conditions (atropine, propranolol, phentolamine) with and without Sub P antagonist ([D-Pro2,D-Trp7,9]-Sub P), VIP antagonist ([D-p-Cl-Phe6,Leu17]-VIP), and the NO-synthase inhibitor L-NNA (L-NG-nitro arginine). Data are Mean±SEM in % of baseline contractile activity or seconds of inhibition. Results: EFS at 50 Hz increased contractile activity in NC but not in T/A-8 and SBT-8 and the Sub P antagonist blocked contractile activity during EFS at 50Hz in NC (146±18 vs. 85±22%; (without vs. with Sub P antagonist); p=0.04), SBT-8 (92±24 vs. 33±14%; p=0.005), but not in T/A-8 (98±43vs. 95±40 %; p=0.92). VIP antagonist had no effect. Inhibition caused by EFS at 50Hz was of longer duration in SBT-8 vs. NC (5.1±0.7 vs. 2.9±0.2sec; p<0.02). Neither Sub P nor VIP antagonist altered duration of inhibition. EFS at 6Hz inhibited contractile activity markedly in all groups (NC: 46±12; T/A-8: 23±12; SBT-8: 29±11%; p<0.02); this inhibition was reversed by L-NNA in all groups (NC: 103±11; T/A-8: 77±22; SBT-8: 66±29%; p<0.02), but not by the VIP antagonist. In the presence of both L-NNA and VIP antagonist, contractile activity at 6Hz was greater in NC compared to T/A-8 and SBT-8 (154±24 vs. 66±18 and 52±20%; p<0.02), while the duration of inhibition was longer in SBT-8 vs. NC (7.2±.0.6 vs. 4.4±0.3sec; p<0.02). Conclusions: Our data suggest that the chronic effects of denervation as induced by T/A and SBT may blunt the release of excitatory NANC neurotransmitters; Sub P release after SBT is preserved. In contrast, changes in VIP signaling are acute and reversible. Changes in the NANC inhibitory response after extrinsic denervation appear to be mediated via NO rather than VIP. These effects to extrinsic denervation may alter enteric motor function after small bowel transplantation.