Neuronal adrenergic and muscular cholinergic contractile hypersensitivity in canine jejunum after extrinsic denervation

Histologic and immunohistochemical evaluation of intestinal innervation in dogs with and without intussusception

OBJECTIVE

To assess viability of innervation in bowel segments appearing macroscopically viable from dogs with intussusception.

ANIMALS

7 dogs without gastrointestinal dysfunction that had been euthanized for reasons unrelated to the study (control dogs) and 13 dogs with intussusception that underwent enterectomy and intestinal anastomosis (affected dogs).

PROCEDURES

A total of 31 samples of intestinal tissue were obtained from the control dogs; 28 samples were obtained from affected dogs during surgery. Samples were histologically and immunohistochemically prepared and subjectively scored for degree of vacuolization and staining, respectively. Other data collected included mean muscle cell density of circular and longitudinal muscular layers, ratio between areas of muscular layers, mean number of myenteric plexuses, mean ganglion cell density of myenteric plexuses, and degree of degeneration in neuronal plexuses as estimated through synaptophysin and neuron-specific enolase (NSE) immunoreactivity.

RESULTS

Mean muscle cell density of longitudinal muscular layers, ratio between areas of muscular layers, and synaptophysin immunoreactivity did not differ significantly between affected and control dogs; values of all other variables did. Correlations were evident between mean ganglion cell density in myenteric plexuses and mean muscle cell density in circular muscular layers, degree of neuronal degeneration in myenteric plexuses and NSE immunoreactivity, and degree of neuronal degeneration in myenteric plexuses and mean ganglion cell density of myenteric plexuses.

CONCLUSIONS AND CLINICAL RELEVANCE

Innervation may be impaired in bowel segments that appear macroscopically viable. Therefore, careful evaluation of preserved surgical margins during enterectomy and enteroanastomosis and monitoring of digestive function after surgery are important.

Ex vivo biomechanical, functional, and immunohistochemical alterations of adrenergic responses in the female urethra in a rat model of birth trauma

Birth trauma and pelvic injury have been implicated in the etiology of stress urinary incontinence (SUI). This study aimed to assess changes in the biomechanical properties and adrenergic-evoked contractile responses of the rat urethra after simulated birth trauma induced by vaginal distension (VD). Urethras were isolated 4 days after VD and evaluated in our established ex vivo urethral testing system that utilized a laser micrometer to measure the urethral outer diameter at proximal, middle, and distal positions. Segments were precontracted with phenylephrine (PE) and then exposed to intralumenal static pressures ranging from 0 to 20 mmHg to measure urethral compliance. After active assessment, the urethra was rendered passive with EDTA and assessed. Pressure and diameter measurements were recorded via computer. Urethral thickness was measured histologically to calculate circumferential stress-strain response and functional contraction ratio (FCR), a measure of smooth muscle activity. VD proximal urethras exhibited a significantly increased response to PE compared with that in controls. Conversely, proximal VD urethras had significantly decreased circumferential stress and FCR values in the presence of PE, suggesting that VD reduced the ability of the proximal segment to maintain smooth muscle tone at higher pressures and strains. Circumferential stress values for VD middle urethral segments were significantly higher than control values. Histological analyses using antibodies against general (protein gene product 9.5) and sympathetic (tyrosine hydroxylase) nerve markers showed a significant reduction in nerve density in VD proximal and middle urethral segments. These results strongly suggest that VD damages adrenergic nerves and alters adrenergic responses of proximal and middle urethral smooth muscle. Defects in urethral storage mechanisms, involving changes in adrenergic regulation, may contribute to stress urinary incontinence induced by simulated birth trauma.

Role of selective alpha and beta adrenergic receptor mechanisms in rat jejunal longitudinal muscle contractility

Gut motility is modulated by adrenergic mechanisms. The aim of our study was to examine mechanisms of selective adrenergic receptors in rat jejunum. Spontaneous contractile activity of longitudinal muscle strips from rat jejunum was measured in 5-ml tissue chambers. Dose-responses (six doses, 10(-7) -3 x 10(-5)M) to norepinephrine (NE, nonspecific), phenylephrine (PH, alpha1), clonidine (C, alpha2), prenalterol (PR, beta1), ritodrine (RI, beta2), and ZD7714 (ZD, beta3) were evaluated with and without tetrodotoxin (TTX, nerve blocker). NE(3 x 10(-5)M) inhibited 74 +/- 5% (mean +/- SEM) of spontaneous activity. This was the maximum effect. The same dose of RI(beta2), PH(alpha1), or ZD(beta(3)) resulted in an inhibition of only 56 +/- 5, 43 +/- 4, 33 +/- 6, respectively. The calculated concentration to induce 50% inhibition (EC50) of ZD(beta3) was similar to NE, whereas higher concentrations of PH(alpha1) or RI(beta2) were required. C(alpha2) and PR(beta1) had no effect. TTX changed exclusively the EC50 of RI from 4.4 +/- 0.2 to 2.7 +/- 0.8% (p < 0.04). Contractility was inhibited by NE (nonspecific). PH(alpha1), RI(beta2), and ZD(beta3) mimic the effect of NE. TTX reduced the inhibition by RI. Our results suggest that muscular alpha1, beta2, and beta3 receptor mechanisms mediate adrenergic inhibition of contractility in rat jejunum. beta2 mechanisms seem to involve also neural pathways.

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.

Nitrergic mechanisms mediating inhibitory control of longitudinal smooth muscle contraction in mouse small intestine

Studies using genetic manipulation to investigate mechanisms of control of physiologic function often necessitate mouse models. However, baseline functional analysis of murine small intestinal motility has not been well defined. Our aim was to define nitrergic mechanisms regulating mouse small intestinal longitudinal muscle. Endogenous nitric oxide (NO) is an important neuroregulatory substance mediating inhibition of contractile activity in murine small bowel. Full-thickness muscle strips of jejunum and ileum from C57BL/6 mice (n > or =6 mice) cut in the direction of longitudinal muscle were studied. Numerous conditions of electrical field stimulation (EFS) and effects of exogenous NO and NO donors were studied in the absence or presence of inhibitors of nitric oxide synthase (NOS) and 1H-[1,2,4]-oxadiazaolo-[4,3-a]-quinoxalin-1-one (ODQ), a downstream inhibitor of guanylyl cyclase. EFS induced a frequency-dependent inhibition of contractile activity in both jejunum and ileum (P < 0.05). As the voltage of EFS was increased, inhibition turned to excitation in the jejunum; in contrast, the ileum demonstrated a voltage-dependent increasing inhibition (P < 0.05 each). EFS-induced inhibition was blocked by NOS inhibitors and ODQ. NO donors inhibited spontaneous contractile activity abolished by ODQ. NO appears to be an endogenous inhibitory neurotransmitter in murine longitudinal small bowel muscle. Nitrergic mechanisms mediate inhibitory control of murine longitudinal small intestinal muscle. Differences exist in neuroregulatory control between jejunum and ileum that may be related to their known difference in motor patterns.

Chronic extrinsic denervation of the small bowel: effect on adrenergic and cholinergic contractile mechanisms in canine ileal circular muscle

BACKGROUND

Small bowel transplantation necessitates chronic extrinsic denervation and is often followed by enteric dysfunction. Our aim was to study canine ileal contractile activity after extrinsic denervation.

METHODS

In vitro dose responses to cholinergic and adrenergic agonists were evaluated in canine ileal muscle strips in control subjects and after jejunoileal extrinsic denervation (EX DEN) at 0, 2, and 8 weeks after operative preparation.

RESULTS

Spontaneous activity and the increased activity after tetrodotoxin (enteric nerve blockade) did not differ between groups. Response to acetylcholine and bethanechol did not differ at any time in the control or EX DEN group. In contrast, the EX DEN group demonstrated a procontractile hypersensitivity to norepinephrine at 2 and 8 weeks that was not seen in the control group. This adrenergic hypersensitivity in the EX DEN group was insensitive to intramural neural blockade with tetrodotoxin.

CONCLUSIONS

Extrinsic denervation does not affect basal contractile activity, augmented contractile activity to intramural neural blockade, nor response to cholinergic agonists. However, it induces a procontractile adrenergic hypersensitivity in canine ileal circular muscle mediated at the level of the smooth muscle and not at the enteric nervous system.