| Background and AimsGastrointestinial tract is an important endocrine organ.Gastrointestinal motility function plays a key role on the regulation of blood glucose.On one hand,hyperglycemia may affect intestineal motility and cause some discomfort symptoms,such as nausea,vomiting,abdominal pain and bloating;on the other hand,intestinal motility alters nutrient absorption and thus affects blood glucose.Therefore,methods which focus on alteration gastrointestinal motility can be used to treat hyperglycemia.Gastrointestinal myoelectrical activity is closely related to gastrointestinal motility.Gastric dysrhythmias are known to be associated with hyperglycemia.However,little is known whether hyperglycemia also produces small intestinal dysrhythmias for difficulty on the recording of small intestineal myoelectrical activety.Autonomic neuropathy is thought to be an important causal factor in motility disorders of diabetes mellitus（T2DM）.However,it is unknown whether impairment in autonomic functions plays a role in hyperglycemia-induced slow wave dysrhythmias.Therefore,we explored the effects of hyperglycemia on intestineal myoelectrical activeity and the role of autonomic functions in hyperglycemia.Our preliminary data showed that intestinal electrical stimulation（IES）may affect gastrointestinal motility,gut hormones secretion,nutrient absorption and body weight loss,which is proposed as a potential treatment for T2 DM.This study aimed to investigate the acute and chronic effects and the mechanism of IES on hyperglycemia in a rodent model of type 2 diabetes.The mechanism of IES on hypoglycemia role was also explored from gastrointestinal motility,gut hormones,food intake,body weight and islet functions.Methods1.Hyperglycemia-induced small intestinal dysrthmias attributed to sympathyovagal imbalance（1）Preparations of animals: The mle Goto-Kakizaki（GK）spontaneously diabetic rats and control male Wistar Kyoto（WKY）rats were included.Each animals was implanted a pair of myocardial pacing wires on the duodenal serosa and there electodes on the subcutaneous of anterior chest wall.（2）Recording of small intestinal myoelectrical activity: The spectral analyzing method was used for small intestinal myoelectrical activity and Electrocardiogram（ECG）signals analysis.The parameters for small intestinal myoelectrical activity were involved the dominant frequency（DF）and the dominant power（DP）of slow wave,the percentage of normal small intestinal slow waves（% of NSW）and number of spike bursts per minute.The heart rate variability signal was derived from low frequency（LF）and high frequency（HF）parameters.The ratio of LF/HF reflected sympthovagal balance.（3）Oral glucose tolerance test（OGTT）and glycated hemoglobin levels were measured and the area under the curve（AUC）of blood glucose was calculated.（4）In another ecperiment,the WKY rats were injected with glucagons to induce hyperglycemia.The change of blood glucose level,small intestinal myoelectrical activity and cardiac autonomic functions were recorded.（5）The correlation between blood glucose levels and the regularity of small intestineal slow waves were analzed.2.The effects and mechanism of acute smalll intestinal electrical stimulation on blood glucose regulation for type 2 diabetes（1）Preparations of animals: Twenty mle GK rats and 10 control male WKY rats were included.Each animals was implanted a pair of myocardial pacing wires on the duodenal serosa and the wires were percutaneously tunneled through the anterior abdominal wall to the back of the neck.（2）Grouping and parameter setting: Two sets of the parameters were chosen based on previous experiments.Parameter 1 was set as 0.6s on,0.9s off,40 Hz,3ms,2m A which was believed to alter GI motility.Parameter 2 was the same as parameter 1 except the pulse width was 0.3ms,which was reported to increase neuronal activity.No stimulation was performed in the sham group.（3）After an overnight fast,OGTT and insulin resistant test（ITT）was performed with or without IES.OGTT was conducted by oral feeding of 20% glucose（1g/kg）then the blood glucose level was measured at 0,15,30,60,90,120 and/or180 min.ITT followed the same protocol except that insulin（0.5U/kg）was injected prior to the glucose feeding.Plasma GLP-1 and insulin level were measured synchronously during OGTT.（4）In two OGTT sessions,either Exendin-9（GLP-1 antagonist）or Exendin-9 plus IES were performed to investigate the mechanism of IES.（5）Gastric emptying and small bowl transit were also tested after rat’s euthanasia.3.The effects and mechanism of chronic smalll intestinal electrical stimulation on blood glucose regulation for type 2 diabetes（1）Preparations of animals: Twenty mle GK rats and 10 control male WKY rats were included.Each animal was chronically implanted one pair of electrodes on the duodenal serosa.The electrode wires were connected to a tether system,which allowed IES to be delivered using an external pulse generator so that rats could move freely in the home cages.（2）Grouping and parameter setting: The GK rats were randomly divided into IES and sham-IES groups.The stimulating parameter was chosen based on previous acute experiments,which was set as 0.6s on,0.9s off,40 Hz,3ms,2m A and continuous stimulation for 12 hours every night for 8 weeks.No stimulation was performed in the sham-IES group and WKY rats.（3）Food intake was continuously and automatically measured by a computerized Bio DAQ system.（4）Body weight,fasting blood glucose（FBG）was measured weekly.（5）OGTT was performed at baseline and at the end of 4th and 8th weeks.（6）Hb A1 c and ITT were obtained at baseline and 8th week.（7）Plasma GLP-1 and insulin level were measured synchronously during the 8th-week OGTT.（8）Pancrease weight,islet morphometry and beta-cell mass were analzed.Results1.Hyperglycemia-induced small intestinal dysrthmias attributed to sympathyovagal imbalance（1）The blood glucose level and the AUC of blood glucose during OGTT were higher in diabetic rats than normal rats.（2）The diabetic rats showed reduced regularity in intestinal slow waves in fasting and fed states（P < 0.001 for both）,and increased sympathovagal balance（P < 0.05）in comparison with the control rats.The regularity in intestinal slow waves was negatively correlated with the Hb A1 c level in all rats（r =-0.663,P = 0.000）.（3）Glucagon injection in the control rats induced transient hyperglycemia,intestinal slow wave dysrhythmias and impaired autonomic functions,similar to those observed in the diabetic rats.（4）The increase in blood glucose was correlated with the decrease in the regularity of intestinal slow waves（r =-0.739,P = 0.015）.2.The effects and mechanism of acute smalll intestinal electrical stimulation on blood glucose regulation for type 2 diabetes（1）During the first 30 min after feeding of glucose,IES-3ms but not IES-0.3ms significantly reduced blood glucose from 388mg/dl in sham-IES to 323mg/dl with IES（P < 0.001）.However,after 30 min,both IES-3ms and IES-0.3ms reduced blood glucose from 60 min to 120 min by 16-20%（P < 0.05 respectively）,no difference was noted between these two parameters.（2）During ITT,there was no difference of the blood glucose level between IES and Sham-IES sessions（P > 0.05 respectively）,suggesting insulin sensitivity was not altered by IES.（3）The GLP-1 antagonist Exendin-9 significantly blocked the inhibitory effect of IES on hyperglycemia from 30 min to 60min（P < 0.05 respectively vs.IES）.（4）IES increased plasma GLP-1 and insulin level at 30min（P < 0.05）.（5）IES accelerated small bowl transit（P = 0.004）,but has no effect on gastric emptying.3.The effects and mechanism of chronic smalll intestinal electrical stimulation on blood glucose regulation for type 2 diabetes（1）After 4 weeks treatments,IES decreased blood glucose only at 30 min after feeding of glucose（P < 0.05）,At 8th week,IES significantly reduced blood glucose from 15 min to 120 min by 20-30%（P < 0.02 at 15 min,30min and P < 0.01 at 60 min,90min,120min）.Blood glucose at 0min was decreased 13%（P < 0.02）.The AUC of blood glucose during OGTT was decreased by 22% with IES（P = 0.002）.（2）IES reduced FBG by10%-15% from 6-8 weeks（P < 0.05 at 6th week,P < 0.01 at 8th week and P = 0.07 at 7th week）.（3）IES trended to reduce body weight and achieved a 10% significant reduction at 8th week（P < 0.05）.No significant difference was noted on the food intake between IES and Sham-IES（P > 0.05）.（4）IES significantly reduced Hb A1 c level by 6% compared to the sham-IES（P<0.05）.The change of Hb A1 c was not correlated with the reduction of body weight（R2 = 0.153,P > 0.05）.（5）The basal,30 min and AUC of plasma GLP-1 concentration after the gavage of glucose during OGTT was increased in IES group,compared to that in sham group.（6）The weight of pancreas（normalized by body weight）in GK rats with sham was significant lower than that of WKY rats（P < 0.05）.The weight of pancreas in GK rats with IES treatment was however,comparable to the control rats（0.27%,P > 0.05）.（7）IES preserved islet architecture by restoring the mass of beta cells.Conclusions1.Both spontaneous and glucagon-induced hyperglycemia results in slow wave dysrhythmias in the small intestine.Impairment in autonomic functions（increased sympathovagal balance）may play a role in hyperglycemia-induced dysrhythmias.2.Acute IES reduced postprandial blood glucose level in a rodent model of type 2 diabetes.The hypoglycemic effect was partially mediated via GLP-1.In addition,both GI motility and neuronal mechanisms are seemed to be involved as well.3.Chronic IES reduces both postprandial and fasting blood glucose level in diabetic rats,possibly attributed to the increasing GLP-1 secretion and improvement in β-cell functions. |
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