Effects And Mechanism Of Sacral Nerve Stimulation For Slow Transit Constipation

Chronic constipation is a common gastrointestinal complaint characterized by decreased bowel movements or defecation straining. It affects 5%-30% of the general population in western country and 4%-6% in China with a higher prevalence in the elder and women. Chronic constipation is considered to impair the quality of life. In the US, it imposes a substantial economic burden, with 1.7 billion in direct and indirect costs. Constipation can be primarily a functional disorder or secondary constipation. Functional constipation can be categorized into 3 subgroups (obstructed defecation, slow transit constipation and normal transit constipation). Slow transit constipation (STC) is a common disorder characterized by decreased bowel movements and hard stools, caused by abnormalities of colonic motility.An ideal animal model offers an opportunity to understand the cause and mechanism of slow transit constipation. A group of international and domestic researchers use different drugs (low fiber diet, laxative, sucralfate, loperamide, morphine, diphenoxylate) to establish the STC models. Loperamide, an opioid-receptor agonist, acts on the opioid receptors in the gut and treat the diarrhea. Studies showed loperamide decrease the bowel movements and increase the colon transit time on rats. Loperamide-induced constipation in a rat model, which coincided with the pathophysiological change in STC patients, is a ideal model. Some studies showed that patients with constipation may have the performance of functional dyspepsia. Forty percent of the patients with chronic constipation had abnormal gastric slow waves and delayed gastric emptying. But it is unknown if the patients with constipation have the abnormal small intestinal slow wave and transit time.Current treatment of constipation includes lifestyle modification (fiber and fluid intake, physical exercise), laxatives (bulk-forming, osmotic, lubricant or stimulant laxatives), biofeedback training, psychosocial treatments and surgery. Although these medications can improve symptoms in patients with constipation, the efficacy and long-term efficacy is still unsatisfactory. A minority of patients with severe constipation fails traditional therapy.Sacral nerve stimulation (SNS) is a new established treatment for STC. It was paid more and more attention as its high efficacy, minimally invasive, and acceptable side effects. A review showed the success rate of SNS for constipation ranged from 42-100 percent. Although the effects of SNS on colon transit have been studied in a few studies, the outcomes are variable. It is not clear the effect of SNS on gastric emptying and small intestinal motility. The mechanisms of of SNS are largely unknown.Part I. The experimental study of gastrointestinal motility in SD rats with slow transit constipaitonAim(1) To measure the distal colon transit time (dCTT), gastric emptying, small intestinal transit time and small intestinal slow wave in a rodent constipation model induced by loperamide. (2) To assess the autonomic nerve function in a rodent constipation model.MethodConstipation in rats was induced by injection of loperamide at the dose of 2 mg/kg twice a day for seven days. The rats were then divided into two groups:control group and slow transit constipation model group. Constipation in rats was induced by subcutaneous injection of loperamide at the dose of 2 mg/kg twice a day for seven days. The rats in control group received subcutaneous injection of saline with same dosage. Number and weight of 24-hour fecal pellets were measured daily in two groups. The gastric emptying, small intestinal transit time, small intestinal slow wave, whole gut transit time (WGTT) and dCTT were assessed. The autonomic nervous function was assessed by Pancreatic polypeptide (PP), norepinephrine (NE), and the spectral analysis of the heart rate variability (HRV).Results① The number of 24-hour pellets was significantly reduced with loperamide in comparison with the control group (35.1±2.5 vs.25.5±3.8,P<0.01). The weight of 24-hour pellets were significantly decreased in the model group compared with control group (7.9±0.8g vs.5.3±0.7g, P<0.01). The dry weight and water content of 24-hour pellets were also decreased in the model group compared with control group (P<0.01). ② Compared with control group, model group increased the dCTT (15.8±3.7 min vs. 31.0±9.4 min, P<0.01). The WGTT was 9.7±2.1h in control group and 14.2±2.3h in model group(P<0.01). Loperamide delayed the gastric emptying (58%±7% vs.39%±7%, P<0.01) and small intestinal transit time (6.6±0.6 vs.4.9±0.8, P<0.01). ③ The dominant frequency was 40.2±2.5 cpm in the control group and 34.8±4.1 cpm in the model group (P<0.01). Loperamide exhibited a decreased percentage of normal slow waves in comparison with the control group (90.8%±3.5% vs.80.7%±4.8%, P<0.01). ④ There was no significant difference between control and model group in LF, HF and LF/HF (P>0.05). There was no significant difference between control and model group in NE and PP (P>0.05).Conclusion(1) This study successfully established the slow transit constipation in a rat model induced by loperamide. (2) The number, weight and water content of 24-hour fecal pellets were decreased in the model group compared with control group. (3) The dCTT, WGTT, gastric emptying, small intestinal transit time was delayed in the model group. Loperamide induced small intestinal dysrhythmias. (4) There was no significant difference between control and model group in autonomic nervous function.Part Ⅱ. The experimental study of sacral nerve stimulation for slow transit constipationAim(1) To observe the effect of SNS on SD rats with slow transit constipation induced by loperamide. (2) To observe the effect of SNS with different frequency and pulse width on dCTT and rectal compliance and get the optimized parameters (3) To observe the effect of SNS with optimized parameters on gastric emptying, small intestinal transit time, small intestinal slow wave, and whole gut transit time (WGTT) in SD rats with slow transit constipation.MethodsExperiment 1:Including two series, SNS was performed in nine normal rats on separate days. The first series included six SNS sessions (5Hz,210μs,90% of motor threshold (MT); 15Hz,210μs,90% of MT; 30Hz,210μs,90% of MT;100μs,15Hz,90% of MT; 500μs,15Hz,90% of MT; 5Hz, 100us,90% of MT). In each session, the distal colon transit time was measured before and after the stimulation. The second series was designed to study the effects of SNS with two sets of parameters on rectal compliance. It included two randomized sessions (5Hz, 100us,90% of MT and 15Hz,210μs,90% of MT). Rectal compliance was measured by Barostat at baseline and during electrical stimulation.Experiment 2:Thirty rats were then divided into three groups:SNS, model group and control group. SNS with parameters optimized in Exp 1, delivered via electrodes chronically placed at S3 sacral nerve unilaterally (right side of the body), four hours daily for 7 days. Number and weight of 24-hour fecal pellets were measured daily. Numerous measurements, including gastric emptying, small intestinal transit time, small intestinal slow wave, WGTT and dCTT, were made after the stimulation.Results① The dCTT was 7.3±2.4 min in 5Hz frequency stimulation (5Hz,210μs,90% MT), increased to 10.4±1.5 min in 15Hz frequency stimulation (15Hz,210μs,90% MT) (P=0.045) and 10.5±3.9 min in 30Hz frequency stimulation (30Hz,210μs,90% MT) (P=0.035). The dCTT was 7.5±2.2 min in 100μs pulse width (15Hz,90% MT) stimulation, increased to 10.4±1.5 min in 210μpulse width (15Hz,90% MT) stimulation (P=0.045) and 10.7±2.9 min in 500μs pulse width (15Hz,90% MT) stimulation (P=0.02). SNS with optimized parameter (5Hz, 100us,90% of MT) decreased the dCTT compared with traditional parameter (15Hz,210μs,90% of MT) (10.4±1.5 min vs.5.1±1.4 min, P<0.01).② In comparison with the traditional parameter (15Hz,210μs,90% of MT), SNS with optimized parameter (5Hz, 100us,90% of MT) increased the rectal compliance (P<0.01). ③ The number of 24-hour pellets was significantly increased with SNS in comparison with the model group (25.5±3.8 vs. 34.5±3.0, P<0.01). The weight and water content of 24-hour pellets were also increased in the SNS group compared with model group (5.1±0.5g vs.7.4±0.4g, P<0.01; 19.4±1.6% vs.26.1±2.8%, P<0.01). ④ Compared with model group, SNS group decreased the dCTT (29.4±3.7 min vs.16.4±5.3 min, P<0.01). There was no significant difference between SNS group and model group in WGTT, gastric emptying, small intestinal transit time, and small intestinal slow wave (P>0.05).Conclusions(1) Lower frequency and pulse width stimulation were better than the higher frequency and pulse width stimulation in distal colon transit tine. (2) In comparison with the traditional parameter (15Hz,210μs,90% of MT), SNS with optimized parameters (5Hz, 100us,90% of MT) decreased the dCTT and increased the rectal compliance. (3) SNS increased the number, weight and water content of 24-hour fecal pellets compared with the model group. (4) SNS decreased the dCTT, but have no effect on WGTT, gastric emptying, small intestinal transit time, and small intestinal slow wave.Part Ⅲ. Mechanism of sacral nerve stimulation for slow transit constipationAimTo evaluate the role of autonomic nervous function in the sacral nerve stimulation and investigate the mechanism of SNS for STC.MethodsExperiment 1:Ten STC rats were test in six randomized sessions with an interval of at least three days:SNS+saline, saline without SNS, Nco-nitro-L-arginine (L-NNA, 10mg/kg)+SNS, L-NNA (10mg/kg) without SNS, atropine (0.5 mg/kg) with SNS and atropine (0.5 mg/kg) without SNS. In a randomized order, each rat was administered saline or atropine intramuscularly 10 min before SNS. SNS (5Hz, 100us,90% of MT) was performed via the pair of electrodes for 4 hours. The distal colon transit time was measured after the stimulation.Experiment 2:Thirty rats were then divided into three groups:SNS, model group and control group. SNS with parameters (5Hz, 100us,90% of MT), delivered via electrodes chronically placed at S3 sacral nerve unilaterally (right side of the body), four hours daily for 7 days. The autonomic nervous function was assessed by the spectral analysis of the heart rate variability (HRV). pancreatic polypeptide (PP), norepinephrine (NE), acetylcholine (Ach) and substance P (SP) were measured with corresponding ELISA kits.Results① There was no significant difference between SNS+L-NNA group and SNS+ saline group in dCTT (16.4±2.3 vs.17.4±4.0, P>0.05). ② Atropine had no accelerative effect on dCTT (28.9±4.9 vs.31.4±3.9, P=0.171). But atropine blocked the effect of SNS on dCTT (29.0±4.1 vs.16.4±2.3, P<0.01). ③ Compared with model group, SNS increased the HF (0.28±0.08 vs.0.37±0.09, P=0.02) and decreased the LF/HF (2.65±0.61 vs.2.73±0.88, P=0.01).④ SNS increased the levels of PP (31.20±1.80 pg/ml vs.40.66±6.09 pg/ml, P<0.01) in the plasma and Ach in the colon (965.89±154.67 pg/ml vs.1267.39±165.12 pg/ml, P<0.01).Conclusions(1) Atropine blocked the accelerative effect of SNS on dCTT. (2) SNS increased vagal activity and reduced sympathetic activity. (3) SNS treated the STC via the cholinergic pathway.