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

Changes in peptidergic neurotransmission during postoperative ileus in rat circular jejunal muscle

BACKGROUND

Our aim was to explore unknown changes in neurotransmission with vasoactive intestinal peptide (VIP) and Substance P (Sub P) during postoperative ileus (POI).

METHODS

Contractile activity of rat circular jejunal muscle strips was studied in five groups (n = 6/group): Naïve controls, sham controls 12 h and 3 days after laparotomy, and rats 12 h, 3 days after induction of POI. Dose-responses to VIP (10(-10) -10(-7) M), Sub P (3 × 10(-10) -3 × 10(-7) M), and electrical field stimulation (EFS, to study endogenous release of neurotransmitters) were studied with different antagonists. Intestinal transit, inflammatory cells and immunoreactivity for VIP and Sub P were investigated in the bowel wall and cellular Finkel osteo sarcoma expression was determined in vagal afferent and efferent nuclei of the brainstem.

KEY RESULTS

Postoperative ileus characterized by delayed intestinal transit and intramural inflammation was associated with an increased inhibitory effect of VIP on contractile activity. A biphasic impact was observed for Sub P with a decrease in its excitatory potential on contractility at 12 h, followed by a later increase 3 days postoperatively. Inhibitory response to EFS was increased, whereas the excitatory response decreased in ileus animals. VIP expression was increased in all postoperative animals while only animals 3 days after ileus induction showed increased Sub P expression in the myenteric plexus. These changes were associated with an activation of afferent but not efferent vagal nuclei in the brain stem.

CONCLUSIONS & INFERENCES

Specific, time-dependent changes in peptidergic neurotransmission with VIP and Sub P occur during POI that are associated with vagal afferent activation, but are independent of the activation of efferent vagal pathways.

Changes in beta-adrenergic neurotransmission during postoperative ileus in rat circular jejunal muscle

BACKGROUND

To explore postoperative changes in β-adrenergic neurotransmission that participate in pathophysiology of postoperative ileus.

METHODS

Contractile activity of circular jejunal muscle strips was studied. Groups (n = 6/group) were: naïve controls, sham controls 1 and 7 days after laparotomy, and rats 12 h, 1, 3, and 7 days after laparotomy with standardized small bowel manipulation (postoperative ileus). Dose-responses to the β-agonist isoprenaline (3 × 10(-10) - 10(-7) mol L(-1)) were studied in presence/absence of tetrodotoxin (global neural blockade; 10(-6) mol L(-1) ), N6-(1-iminoethyl)-l-lysine (inhibition of inducible nitric oxide synthesis; 10(-4) mol L(-1)), nimesulide (cyclooxygenase-2 inhibition; 10(-5) mol L(-1)), or propranolol (β-blockade; 5 × 10(-6) mol L(-1)). Histochemistry for inflammatory cells and intestinal transit were studied.

KEY RESULTS

Intramural inflammation and delayed transit (postoperative ileus) occurred only in ileus groups. The inhibitory potential of isoprenaline decreased in all postoperative groups including sham (P < 0.05). Tetrodotoxin enhanced isoprenaline-induced inhibition in ileus and sham groups (P < 0.05). N6-(1-iminoethyl)-l-lysine and nimesulide decreased isoprenaline-induced inhibition in ileus groups 12 h, 1, and 7 days, and in sham controls 7 days postoperatively (P < 0.05). Propranolol prevented isoprenaline effects in all groups (P < 0.05).

CONCLUSIONS & INFERENCES

Inhibitory effects of isoprenaline on contractile activity were decreased for 7 days postoperatively. Changes in β-adrenergic neurotransmission do not induce postoperative ileus and appear to be caused by anesthesia and laparotomy rather than bowel manipulation.

Role of hydrogen sulfide as a gasotransmitter in modulating contractile activity of circular muscle of rat jejunum

AIM

Our aim was to determine mechanisms of action of the gasotransmitter hydrogen sulfide (H(2)S) on contractile activity in circular muscle of rat jejunum.

METHODS

Jejunal circular muscle strips were prepared to measure isometric contractions. Effects of sodium hydrosulfide (NaHS), a H(2)S donor, were evaluated on spontaneous contractile activity and after pre-contraction with bethanechol. L-cysteine was evaluated as an endogenous H(2)S donor. We evaluated extrinsic nerves, enteric nervous system, visceral afferent nerves, nitric oxide, K(ATP)+ and K(Ca)+ channels, and myosin light chain phosphatase on action of H(2)S using non-adrenergic/non-cholinergic conditions, tetrodotoxin, capsaicin, L-N(G)-nitro arginine (L-NNA), glibenclamide, apamin, and calyculin A, respectively, and electrical field stimulation (EFS).

RESULTS

NaHS dose-dependently and reversibly inhibited spontaneous and bethanechol-stimulated contractile activity (p < 0.05). L-cysteine had a dose-dependent inhibitory effect. Non-adrenergic/non-cholinergic conditions, tetrodotoxin, capsaicin, L-NNA, or apamin had no effect on contractile inhibition by NaHS; in contrast, low-dose glibenclamide and calyculin A prevented NaHS-induced inhibition. We could not demonstrate H(2)S release by EFS.

CONCLUSIONS

H(2)S inhibits contractile activity of jejunal circular muscle dose-dependently, in part by K(ATP)+ channels and via myosin light chain phosphatase, but not via pathways mediated by the extrinsic or enteric nervous system, visceral afferent nerves, nitric oxide, or K(Ca)+ channels.

Hydrogen sulfide modulates contractile function in rat jejunum

BACKGROUND

Effects of hydrogen sulfide (H(2)S), a third gasotransmitter of the gut, are not well understood. The aim of this study was to determine effects/mechanisms of H(2)S action on contractile function in rat jejunal muscle.

METHODS

Transmural strips of longitudinal muscle were evaluated. Response to sodium hydrosulfide (NaHS, H(2)S donor; 10(-5)-10(-3)M) was studied on spontaneous contractile activity and after precontraction (bethanechol, 3 × 10(-6)M). Atropine, propranolol, phentolamine, tetrodotoxin, capsaicin, L-N(G)-nitro arginine (L-NNA), and glibenclamide were used to determine mechanisms. L-cysteine (10(-4)-10(-2)M; substrate for H(2)S production) and aminooxyacetic acid and DL-propargylglycine (inhibitors of enzymes generating H(2)S endogenously) were used to study endogenous production. Aminooxyacetic acid, DL-propargylglycine, L-NNA, and vasoactive intestinal polypeptide (VIP) antagonist [D-p-Cl-Phe(6),Leu(17)]-VIP were used to study H(2)S release during electrical field stimulation (EFS) and interaction with VIP and nitric oxide. Immunohistofluorescence of jejunal whole mounts was performed for endogenous H(2)S-producing enzymes.

RESULTS

Cystathionine-β-synthase and cystathionine-γ-lyase were expressed only in myenteric plexus. NaHS suppressed spontaneous and stimulated contractile activity (P < 0.01). Glibenclamide prevented some suppression by NaHS (P = 0.01) of stimulated contractile activity but did not prevent suppression of spontaneous contractile activity. Other drugs had no effect on spontaneous contractile activity but increased inhibitory effects of NaHS on spontaneous and stimulated contractile activity (P < 0.05). L-cysteine had no effects on contractile activity. Inhibitors altered basal and stimulated activity suggesting endogenous release of H(2)S.

CONCLUSIONS

H(2)S presumably suppresses contractile activity in jejunum by direct effects on smooth muscle. Mechanism(s) of inhibition remains unclear, because blocking known neurotransmitters enhanced H(2)S-induced suppression, while blocking adenosine triphosphate (ATP)-sensitive K(+)-channels did not block H(2)S-induced inhibition.

Mechanisms of action of the gasotransmitter hydrogen sulfide in modulating contractile activity of longitudinal muscle of rat ileum

AIM

This study aims to determine mechanisms of action of the gasotransmitter hydrogen sulfide (H(2)S) on contractile activity in longitudinal muscle of rat ileum.

METHODS

Ileal longitudinal muscle strips were prepared to measure isometric contractions. Effects of sodium hydrosulfide (NaHS), a donor of H(2)S, were evaluated on spontaneous contractile activity and after enhanced contractile activity with bethanechol. L-cysteine was evaluated as a potential endogenous donor of H(2)S. We evaluated involvement of extrinsic nerves, enteric nervous system, visceral afferent nerves, nitric oxide, and K(ATP)(+) channel and K(Ca)(+) channel activity on the action of H(2)S using non-adrenergic/non-cholinergic conditions, tetrodotoxin, capsaicin, L-N(G)-nitro arginine (L-NNA), glibenclamide, and apamin, respectively, as well as electrical field stimulation.

RESULT

NaHS dose-dependently and reversibly inhibited spontaneous and bethanechol-stimulated contractile activity (p < 0.05). L-cysteine had no inhibitory effect. Non-adrenergic/non-cholinergic conditions, tetrodotoxin, capsaicin, L-NNA, glibenclamide, or apamin had no major effect on total contractile activity by NaHS, although both tetrodotoxin and apamin decreased the frequency of bethanechol-enhanced contractile activity (p < 0.05). We could not demonstrate H(2)S release by electrical field stimulation but did show that inhibition of cystathionine β synthase, an endogenous source of H(2)S, augmented the inhibitory effect of low-frequency electrical field stimulation.

CONCLUSION

H(2)S inhibits contractile activity of ileal longitudinal muscle dose-dependently but not through pathways mediated by the extrinsic or enteric nervous system, visceral afferent nerves, nitric oxide, K(ATP)(+) channels, or K(Ca)(+) channels.