Intestinal denervation contributes to enteric dysfunction after small bowel transplantation (SBT).
AIM: To determine effects of chronic extrinsic denervation on motor function mediated by nonadrenergic, noncholinergic (NANC) neurotransmitters substance P (Sub P) and vasoactive intestinal polypeptide (VIP).
HYPOTHESIS: The extrinsic denervation of SBT decreases both excitatory and inhibitory responses mediated by Sub P and VIP, resp.
Methods: Jejunal circular muscle strips (n=8 per rat) were obtained from 6 naïve control rats (NC) and 6 rats 1 year after syngeneic (no immune phenomena) jejunoileal SBT. Exogenous Sub P and VIP (3x10^-9-3x10^-7M) were studied under NANC-conditions without and with the Sub P antagonist [D-Pro²,D-Trp^7,9]-Sub P, the VIP antagonist [D-p-Cl-Phe⁶,Leu¹⁷]-VIP, and the NO-synthase inhibitor L-N^G-nitro arginine (L-NNA). Electrical field stimulation (EFS; to release neurotransmitters) was applied at 3, 6, and 20 Hz. Data are x±SEM change of baseline contractile activity in [%] (increase: positive; decrease: negative value). Immunohistoflourescence (IHF) was performed for tyrosine hydroxylase (TH; sympathetic innervation).
Results: Spontaneous contractile activity did not differ between groups (NC: 4.6±0.5 vs SBT: 6.4±1.0 g^.5 min/mg tissue; ns). VIP inhibited contractile activity dose-dependently in both groups, greater in NC (-87±10 vs -55±17% at VIP 3x10^-7M [highest dose]; p<0.003). Neither VIP antagonist nor L-NNA prevented the inhibitory effect of exogenous VIP. Sub P increased contractile activity dose-dependently, greater in NC (140±42 vs 63±14% at Sub P 3x10^-7M [highest dose]; p<0.02). The effect of exogenous Sub P was reversed completely by the Sub P antagonist (NC: 0±9 and SBT: 11±6% at Sub P 3x10^-7M; p<0.001). The VIP antagonist did not alter the EFS-induced inhibitory response at 3 and 6 Hz in either group, but when NO was blocked with L-NNA, the VIP antagonist further reversed the inhibitory response to 6 Hz compared to NANC conditions in NC (65±43 vs 133±69%; p<0.05), but not in SBT (39±33 vs 127±60%; ns). The excitatory response to EFS at 20 Hz was blocked by the Sub P antagonist in NC (222±33 vs -3±15%; p<0.05), but not in SBT (178±80 vs 86±33%; ns). IHF showed TH staining in SBT suggesting sympathetic reinnervation.
Conclusions: In rat jejunal circular muscle after chronic denervation, inhibitory and excitatory responses to exogenous and neurally released (EFS) VIP and Sub P are decreased. These changes in balance of inhibitory and excitatory neuroregulatory pathways might contribute to enteric dysfunction after SBT and occur despite extrinsic reinnervation. Supported by NIH DK39337 (MGS) and DFG KA 2329/1-1 (MSK).