Influence Of Different Intravenous Anesthetic Agents On Contraction Of Colonic Longitudinal Muscle In Rats

Background and Objective Intravenous anesthetic agents are widely used for pre-anesthetic medication, induction and maintenance of general anesthesia and sedation in the intensive care unit owing to its high-efficiency, no pollution and no irritation to the respiratory tract and so on. However, intravenous anesthetic agents may lead to gastrointestinal adverse reactions such as bellyache, bloating and constipation. Reasons for these effects are complex, influence of intravenous anesthetic agents on contraction of gastrointestinal tract mediated by enteric nervous system (ENS) and smooth muscle cells (SMC) might be involved.The enteric nervous system (ENS) is a collection of80to100million neurons in the gastrointestinal tract and can function independently of the central nervous system (CNS). In the enteric nervous system, the nerve-cell bodies are grouped into small ganglia that are connected by bundles of nerve processes forming two major plexuses, called the myenteric plexus and the submucous plexus. The neurons in the submucous plexus innervating glandular epithelium, intestinal endocrine cells and submucous blood mucosa, controls absorption, blood flow and neuroimmunity. While the myenteric plexus plays an important role in the contraction of gastrointestinal tract smooth muscle. The regulation of smooth muscle cells (SMC) is generally connected with capacitative Ca2+entry (CCE) and/or myofilament Ca2+sensitive in gastrointestinal tract smooth muscle.There are limited data on effects of anesthetic agents on gastrointestinal motility. For that reason, we studied the influence of midazolam, propofol, etomidate and ketamine on contraction of colonic longitudinal muscle in rats by recording the average tension of colonic strips and the mechanism might be involved using tetrodotoxin (TTX).Methods Longitudinal muscle strips of colon were dissected from male Wistar rats and randomly divided into control group and experimental group which included TTX-free group and TTX group. Some strips were exposed to Kreb’s solution with1‰DMSO (control group). Some other strips were incubated into Kreb’s solution containing midazolam, propofol, etomidate and ketamine with (TTX group) or without (TTX-free group) tetrodotoxin pre-treatment. Isometric contraction of longitudinal smooth muscle strips was measured and recorded.Result1.1‰DMSO exerted no effect on tension of colonic strips in control group.2. Midazolam, propofol, etomidate and ketamine at accumulating concentration of1×10-5mol/L,1×10-5mol/L,1×10-6mol/L and3×10-6mol/L decreased the tension of colonic strips in a concentration-dependent manner (P<0.05～0.01) in TTX-free group.3. Pre-treated with TTX to block the generation and conduction of neuron action potential, the tension of colonic strips enhanced.4. Pre-treated with TTX, midazolam, propofol and etomidate produced greater reduction of strip tension in TTX group than that in TTX-free group, while ketamine enhanced strip tension in the presence of TTX.Conclusion The findings of present study demonstrated that midazolam, propofol, etomidate and ketamine exhibited inhibitory effects on spontaneous contractile activities of isolated colonic strips in rats. The probable mechanisms are that midazolam, propofol and etomidate inhibit both the contraction of smooth muscle cells and activity of enteric nervous system, while ketamine increases the contraction of smooth muscle cells and activity of enteric nervous system with a greater enhancement on enteric nervous system than on colonic smooth muscle.