Functional changes in nonadrenergic, noncholinergic inhibitory neurons in ileal circular smooth muscle after small bowel transplantation in rats

Effects of extrinsic denervation on innervation with VIP and substance P in circular muscle of rat jejunum

Extrinsic denervation contributes to enteric motor dysfunction after small bowel transplantation (SBT). Our aim was to determine changes in nonadrenergic, noncholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P (Sub P) in rat jejunal circular muscle after SBT. Muscle strips were studied in tissue chambers from six groups of rats (n > or = 6 per group): naïve controls (NC), animals 1 week after anaesthesia/sham celiotomy (SC-1), and 1 and 8 weeks after jejunal and ileal transection/reanastomosis (TA-1, TA-8) and after syngeneic, orthotopic SBT (SBT-1, SBT-8). Response to exogenous VIP and Sub P and their endogenous release during electrical field stimulation (EFS) were studied. Exogenous VIP and Sub P caused a dose-dependent inhibition and stimulation of mechanical activity in all groups respectively (P < 0.05). The responses to VIP and Sub P were decreased (compared to NC) in all groups at 1 and 8 weeks postoperatively. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) did not prevent the inhibition by exogenous VIP in any group, while the Sub P antagonist ([D-Pro(2),D-Trp(7,9)]-Sub P) prevented the effect of exogenous Sub P in NC, TA-8 and SBT-8 (P < 0.05). Responses to exogenous VIP were unaffected by the nitric oxide synthase inhibitor l-N(G)-nitro arginine and precontraction of muscle strips with Sub P. Endogenous release of VIP and Sub P during EFS was preserved after SBT. In circular muscle of rat jejunum, changes in neuromuscular transmission with VIP and Sub P during the first 8 weeks after SBT are not mediated by extrinsic denervation.

Effect of chronic, extrinsic denervation on functional NANC innervation with vasoactive intestinal polypeptide and substance P in longitudinal muscle of rat jejunum

Intestinal denervation contributes to enteric motor dysfunction after intestinal transplantation [small bowel transplantation (SBT)]. Our aim was to determine long-term effects of extrinsic denervation on functional non-adrenergic, non-cholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P. Contractile activity of jejunal longitudinal muscle from six age-matched, naïve control rats (NC) and eight rats 1 year after syngeneic SBT were studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently in both groups, greater in NC than in SBT. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor l-N(G)-nitro arginine prevented inhibition by exogenous VIP and electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than in SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and increased the EFS-induced inhibitory response. Immunohistofluorescence showed staining for tyrosine hydroxylase in the jejunoileum 1 year after SBT suggesting sympathetic reinnervation. In rat jejunal longitudinal muscle after chronic denervation, response to exogenous VIP and substance P is decreased, while endogenous release of both neurotransmitters is preserved. These alterations in excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

Long-term effects of extrinsic denervation on VIP and substance P innervation in circular muscle of rat jejunum

Intestinal denervation contributes to enteric motor dysfunction after small bowel transplantation (SBT). Our aim was to determine long-term effects of extrinsic denervation on function of nonadrenergic, noncholinergic innervation with substance P and vasoactive intestinal polypeptide (VIP). Contractile activity of jejunal circular muscle strips from six age-matched, naive control rats (NC) and eight rats 1 year after syngeneic SBT was studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently to a comparable degree in both groups. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor L-NG-nitro-arginine did not affect VIP-induced inhibition but increased contractile activity during electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and decreased the excitatory EFS response. Immunohistofluorescence showed tyrosine hydroxylase staining after SBT indicating sympathetic reinnervation. In jejunal circular muscle after chronic denervation, response to exogenous substance P, but not VIP, is decreased, whereas endogenous release of both neurotransmitters is preserved. Alterations in balance of excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

Role of VIP and Substance P in NANC Innervation in the Longitudinal Smooth Muscle of the Rat Jejunum—Influence of Extrinsic Denervation

BACKGROUND

This study was designed to determine changes in nonadrenergic, noncholinergic (NANC) neurotransmission mediated by Vasoactive Intestinal Polypeptide (VIP) and Substance P after small bowel transplantation (SBT).

MATERIALS AND METHODS

Six groups of rats (n > or = 6 per group) were studied: naïve controls (NC); 1 wk after anesthesia/sham celiotomy (SC-1); 1 or 8 wk after jejunal and ileal transection/reanastomosis (TA-1, TA-8), or syngeneic, orthotopic SBT (SBT-1, SBT-8). Jejunal longitudinal muscle strips were studied under NANC-conditions for spontaneous contractile activity, response to exogenous VIP and Substance P, and electrical field stimulation (EFS).

RESULTS

Spontaneous activity did not differ between the six groups. VIP inhibited contractile activity in all groups 1 wk postoperatively (P < 0.05), which was prevented by the NO synthase inhibitor L-N(G)-nitro arginine (L-NNA). In contrast, VIP had no effect in the other groups. Precontraction with Substance P exposed an inhibitory effect of VIP in all groups (P < 0.05 each). Substance P increased contractile activity in all groups, but to a lesser extent in SBT-8 compared with NC, TA-8, and SBT-1 (P < 0.05). The inhibitory effect of EFS at 6 Hz was prevented by L-NNA in NC and TA-8; addition of the VIP antagonist ([D-p-Cl-Phe(6), Leu(17)]-VIP) increased contractile activity in NC, but not in TA-8 and SBT-8. The Substance P antagonist ([D-Pro(2), D-Trp(7,9)]-Substance P) decreased contractile activity during EFS at 50 Hz in NC and SBT-8.

CONCLUSIONS

SBT decreased response to exogenous Substance P, although release of endogenous Substance P (EFS) is preserved. Changes in VIP signaling are acute and reversible and not caused by effects of SBT.

Acute denervation alters the epithelial response to adrenoceptor activation through an increase in alpha1-adrenoceptor expression on villus enterocytes

Loss of sympathetic input due to intestinal denervation results in hypersensitivity and increased intestinal secretion. It is unknown whether denervation-induced alterations in intestinal epithelial physiology are the result of changes in adrenoceptors on enterocytes (ENTs). The purpose of this study was to examine adrenoceptor distribution and pharmacology on small intestinal ENTs following acute intestinal denervation. Lewis rats underwent small bowel transplantation (SBT) or sham operation and proximal small intestinal segments were harvested 1, 2 and 4 weeks postoperatively. Intestinal electrolyte movement was assessed using short-circuit current (Isc) measurements of stripped epithelial sheets following stimulation with phenylephrine (PE), an alpha(1)-adrenoceptor agonist. The presence of adrenoceptor subtypes on separated villus and crypt ENTs was assessed using flow cytometry. Alpha(1)-adrenoceptors were found on approximately 27% of jejunal villus ENTs, but not crypt ENTs, following acute extrinsic denervation. ENTs from the Lewis rat have few beta-adrenoceptors. Alpha(1)-adrenoceptor stimulation of acutely denervated intestinal epithelial sheets decreased Isc by -13.45%. This effect was mediated by a reduction in chloride (Cl(-)) secretion; the absence of Cl(-) reversed the Isc to +13.79%. In conclusion, loss of sympathetic innervation to the gastrointestinal epithelium causes acute upregulation of alpha(1)-adrenoceptors on villus ENTs, leading to inhibition of Cl(-) secretion at the villus tip. The increase in adrenoceptors may reflect a compensatory mechanism to combat the increased secretory state of the bowel due to the loss of the sympathetic innervation and tonic control over intestinal secretion.

Inhibition by nitric oxide and nonadrenergic, noncholinergic (NANC) nerves is preserved in a canine model of extrinsic denervation: Implications for small bowel transplantation

BACKGROUND

Small bowel transplantation (SBT) is complicated by changes in graft motility, especially in the early postoperative period. This dysmotility may be related in part to the extrinsic denervation necessitated by the procedure, but specific neurotransmitter response to SBT is incompletely understood. The aim of this study was to evaluate the role of nitric oxide and nonadrenergic, noncholinergic (NANC) enteric neural input in the nonimmunologic etiology of the dysmotility seen after SBT.

METHODS

A technique of jejunoileal extrinsic denervation (without disruption of mesenteric vascular supply) was used as a model of canine jejunoileal autotransplantation to avoid potential confounding factors such as ischemia-reperfusion and postallotransplant immunologic effects. Longitudinal smooth muscle strips from ileum and jejunum were studied with in vitro tissue chamber methodology at 0, 2, and 8 weeks after this experimental model to explore early and late effects of denervation. Effects of exogenous nitric oxide (NO) and electric field stimulation (EFS), which releases native, endogenous enteric neurotransmitters) were evaluated in neurally intact control dogs and those undergoing extrinsic denervation.

RESULTS

Exogenous NO caused a dose-dependent inhibition of spontaneous contractile activity and in some muscle strips a decrease in basal tone in both groups of dogs. These effects were unchanged by neural blockade with tetrodotoxin and preserved after extrinsic denervation. EFS produced inhibition of spontaneous contractile activity in ileum and a complex, inconsistent response in jejunum. The response to EFS in both ileum and jejunum was unchanged after extrinsic denervation.

CONCLUSIONS

Nitric oxide inhibits contractile activity in canine longitudinal muscle of small bowel. Motility changes seen after this large animal model of extrinsic denervation are not caused by changes in NO or NANC neural function. The variability observed between different segments of intestine is important to consider in the context of SBT.

Substance P and vasoactive intestinal peptide in rat small-bowel isografts

BACKGROUND

It is established that substance P (SP) is released by stimulation of nonadrenergic noncholinergic (NANC) excitatory nerves and vasoactive intestinal peptide (VIP) by stimulation of NANC inhibitory nerves. To evaluate the function of peptidergic nerves such as SP and VIP in small-bowel isografts, we examined the enteric nerve responses to SP and VIP in the isografted rat jejunum, using the normal rat jejunum as a control.

METHODS

Orthotopic entire small bowel transplantation (SBT) with portocaval drainage was performed from Lewis rats to Lewis rats. Grafted tissue specimens were obtained 130 days after SBT (n = 9). As controls, normal segments of the jejunum were obtained from untransplanted Lewis rats (n = 22). A mechanograph was used to evaluate in vitro jejunal responses to electrical field stimulation of the enteric nervous system before and after treatments with various autonomic nerve blockers and neuropeptides (SP and VIP).

RESULTS

SP concentration-dependently mediated the contraction reaction of NANC excitatory nerve in the isografted jejunum and to a lesser extent in the normal jejunum. In addition, there were significant diferences in the percentages showing contraction at 1 x 10(-8) and 1 x 10(-6)g/mL SP between the normal and isografted jejunal muscle strips (P < .05, respectively). VIP concentration dependently mediated the relaxation reaction of NANC inhibitory nerve in the normal jejunum and to a lesser extent in the isografted jejunum. In addition, there was a significant difference between the relaxation frequencies of the normal and those of isografted jejunal muscle strips at 1 x 10(-6) g/mL SP (P < .01).

CONCLUSIONS

Contraction reactions of SP were observed in both the normal and isografted jejunum but were increased in the isografted jejunum. Relaxation reactions of VIP were also observed in both the normal and isografted jejunum but were decreased in the isografted jejunum. The increase of the effects of SP via NANC excitatory nerves and the decrease of the effects of VIP in mediating NANC inhibitory nerves may be largely related to the peristaltic abnormalities seen in the isografted LEW rat jejunum.

Intestinal transplantation

Advances in immunosuppressive treatment as well as better monitoring and control of acute rejection have brought intestinal transplantation (ITx) into the realm of standard treatment for permanent intestinal failure. The results from the intestinal Transplant International Registry (www.intestinaltransplant.org) indicate that ITx is currently an acceptable clinical modality for selected patients with permanent intestinal failure. The goal of this short review is to deal with indications, clinical results and complications of ITx. Although it has been used in humans for the past two decades, very few data are available regarding graft function and its monitoring.

Mechanism mediating nitric oxide-induced inhibition in human jejunal longitudinal smooth muscle

BACKGROUND

Enteric neurotransmission is a complex process involving multiple neurotransmitters, including nitric oxide (NO). Our aim was to evaluate the role and mechanism(s) of action of NO in normal human jejunal longitudinal smooth muscle.

METHODS

Transmural strips of normal human jejunum obtained from subjects undergoing gastric bypass were studied in organ chambers. Effects of exogenous NO (7 x 10(-6) mol/L to 7 x 10(-5) mol/L) and electrical field stimulation (nonspecific release of endogenous neurotransmitters) on spontaneous contractile activity and on precontracted muscle strips (substance P, 10(-5) mol/L) were evaluated in the presence and absence of the competitive NO synthase inhibitor N(G)-amino-L-arginine (L-NNA, 10(-3) mol/L) and the specific soluble guanylyl cyclase inhibitor 1H-[1,2,4]-oxadiazaolo-[4,3-a]-quinoxalin-1-one (ODQ, 10(-5) mol/L and 10(-4) mol/L).

RESULTS

Exogenous NO dose-dependently inhibited spontaneous contractility and relaxed precontracted smooth muscle strips. The effects of NO were markedly attenuated or completely inhibited in the presence of ODQ. Electric field stimulation under nonadrenergic, noncholinergic conditions also inhibited spontaneous contractility and relaxed precontracted smooth muscle strips; both of these effects were attenuated, but not completely inhibited, in the presence of both ODQ and L-NNA.

CONCLUSIONS

NO is an endogenous inhibitory neurotransmitter in human jejunal longitudinal smooth muscle, acting at least in part via a mechanism mediated by guanylyl cyclase. Other (non-nitrergic) nonadrenergic, noncholinergic inhibitory neurotransmitters are likely active in this portion of the human gut.

Chronic extrinsic denervation after small bowel transplantation in rat jejunum: Effects and adaptation in nitrergic and non-nitrergic neuromuscular inhibitory mechanisms

BACKGROUND

Extrinsic denervation of the transplanted small bowel could play a substantial role in motor dysfunction of the transplanted gut. We attempted to determine the effect of chronic extrinsic denervation on intestinal contractility.

METHODS

Jejunal longitudinal muscle strips were obtained from rats 1 week and 8 weeks after (1) syngeneic small bowel transplantation, (2) ischemia/reperfusion, or (3) gut transection/reanastomosis. Nonoperated rats (naive controls) and sham-operated rats (sham controls), 1 week after celiotomy/gut manipulation, served as controls. We evaluated the effects of exogenous nitric oxide, increasing doses of cholinergic and adrenergic agonists, and electrical field stimulation (EFS) in the presence or absence of N(G)-monomethyl-l-arginine, methylene blue, tetraethylammonium, or tetrodotoxin.

RESULTS

Spontaneous contractile activity (_chi +/- SEM), when compared with the naive controls (11.3 +/- 2.0 g.5 min/mg), was increased in all 4 groups at 1 week (15.9 +/- 10 to 19.4 +/- 2 g.5 min/mg; P < or =.03 each) but not at 8 weeks postoperatively. The inhibition of contractile activity by nitric oxide was increased in small bowel transplantation in naive controls at 8 weeks to 80% +/- 10% versus 50% +/- 7% (P <.02). EFS induced an inhibition of contractile activity that was tetraethylammonium- and tetrodotoxin-sensitive but N(G)-monomethyl-l-arginine- and methylene blue-insensitive; the maximal EFS-induced inhibition was increased at 1 week and 8 weeks but only in the small bowel transplantation groups to 103% +/- 5% and 95% +/- 7%, respectively, versus 72% +/- 8% in naive controls (P </=.05).

CONCLUSIONS

[corrected] Increased inhibition of contractile function after small bowel transplantation lasts at least 8 weeks and is mediated by changes in the enteric neuromuscular unit caused by extrinsic denervation.

Intestinal transplantation: indications, results and strategy

The term 'intestinal failure' is now often used to describe gastrointestinal function insufficient to satisfy body nutrient and fluid requirements. The first recognized condition of intestinal failure was short bowel syndrome. Severe motility disorders such as chronic intestinal pseudo-obstruction syndrome in children as well as congenital intractable intestinal mucosa disorders are also forms of intestinal failure, because no curative treatment for these diseases is yet available. Parenteral nutrition and home parenteral nutrition remain the mainstay of therapy for intestinal failure, whether it is partial or total, provisional or permanent. However, some patients develop complications while receiving standard therapy for intestinal failure and are considered for intestinal transplantation. Indeed, recent advances in immunosuppressive treatment and the better monitoring and control of acute rejection have brought intestinal transplantation into the realm of standard treatment for intestinal failure. Although it has been used in humans for the past two decades, this procedure has had a slow learning curve. According to the current results, this challenging procedure may be performed in children or adults, only under certain conditions.

Nitric oxide pathways in circular muscle of the rat jejunum before and after small bowel transplantation

Previous studies suggest that nitric oxide synthase is upregulated after small bowel transplantation which may have implications in enteric dysfunction after small bowel transplantation. The aim of this study was to determine the role of nitric oxide in nonadrenergic, noncholinergic inhibitory function after small bowel transplantation in rat jejunal circular muscle. The following four groups of rats (n = >/=8 rats per group) were studied: Neurally intact control animals; 1 week after anesthesia and sham celiotomy, and either 1 week or 8 weeks after isogeneic, orthotopic small bowel transplantation. Full-thickness jejunal circular muscle strips were evaluated under isometric conditions for spontaneous contractile activity, response to electrical field stimulation, and effects of exogenous nitric oxide and nitric oxide antagonists. Spontaneous activity did not differ among groups. Electrical field stimulation inhibited activity similarly in all groups. Exogenous nitric oxide, NG-monomethyl L-arginine monoacetate salt (a nitric oxide synthase inhibitor), and methylene blue (cGMP antagonist) had no effect on spontaneous activity. Neither nitric oxide antagonist altered the inhibitory response to neural excitation by electrical field stimulation in any group. Nitric oxide, a known inhibitory neurotransmitter in other gut smooth muscle, has no apparent role in rat jejunal circular muscle before or after small bowel transplantation.

Small bowel transplantation induces adrenergic hypersensitivity in ileal longitudinal smooth muscle in rats

Our aim was to determine the effects of small bowel transplantation on contractility of longitudinal muscle in the rat ileum. Full-thickness longitudinal muscle strips from four groups of rats (naive controls, sham-operated controls, and 1 week and 8 weeks after syngeneic orthotopic small bowel transplantation) were studied in vitro. Neither baseline contractility nor response to neural blockade (tetrodotoxin) or adrenergic/cholinergic blockade differed among the groups. Although the dose response to the cholinergic agonist bethanechol and to nitric oxide did not differ among groups, the ED50 (negative log of concentration giving half-maximal effect) for the adrenergic agonist norepinephrine was increased l week and 8 weeks after transplantation, indicating a hypersensitivity response not blocked by tetrodotoxin. Nonadrenergic, noncholinergic inhibitory responses to electrical field stimulation were of greater amplitude and occurred at lesser frequencies (>/=5 Hz) 1 week after small bowel transplantation, but returned to control values 8 weeks postoperatively. These inhibitory responses were blocked by the nitric oxide synthase inhibitor L-NMMA but not by methylene blue, a nonspecific inhibitor of guanylate cyclase. Small bowel transplantation induces a persistent adrenergic denervation hypersensitivity at the muscle and appears to upregulate, at least transiently, other inhibitory mechanisms mediated by neural release of nitric oxide. Small bowel transplantation does not alter muscle response to cholinergic pathways. These alterations in smooth muscle contractility may affect gut function early after clinical small bowel transplantation.