Chronic intestinal electrical stimulation improves glucose intolerance and insulin resistance in diet-induced obesity rats

Small Intestinal Slow Wave Dysrhythmia and Blunted Postprandial Responses in Diabetic Rats

BACKGROUND

Gastric dysmotility and gastric slow wave dysrhythmias have been well documented in patients with diabetes. However, little is known on the effect of hyperglycemia on small intestine motility, such as intestinal slow waves, due to limited options in measuring its activity. Moreover, food intake and digestion process have been reported to alter the small intestine motility in normal rats, but their roles in that of diabetic rats remains unknown. This study aimed to explore the effect of hyperglycemia on small intestinal myoelectrical activity (IMA) and responses to various meals in diabetic and normal rats.

METHODS

IMA was recorded via chronically implanted serosal electrodes in the proximal small intestine in rats with type 2 diabetes induced by high-fat diet feeding followed by a low dose of streptozotocin (30 mg/kg) and normal rats. The percentage of normal slow wave (%NSW), dominant power, and dominant frequency (DF) were assessed from the IMA under various conditions. Oral glucose tolerance test was performed, and blood was collected via the tail vein at baseline and 15, 30, 60, 90, 120, and 180 min after glucose administration for the measurement of blood glucose. Regular laboratory chow, high-fat diet, and small or large nutrient liquid meal were used to explore IMA responses to different meals in diabetic and normal rats.

RESULTS

(1) Compared with a postprandial increase in DF in normal rats (p = 0.007), diabetic rats showed a blunted postprandial response in DF (p = 0.145) after a regular chow. However, no difference was found in %NSW between diabetic and normal rats in both fasting and fed states; (2) In the fasting state, %NSW was correlated with the blood glucose level in diabetic rats (r = -0.817, p = 0.004, N = 8) as well as HbA1C (r = -0.871, p = 0.005, N = 8). After glucose administration, the increase in blood glucose was correlated with a decrease in %NSW (r = -0.655, p < 0.001, N = 8). (3) %NSW in diabetic rats during the 30-min postprandial state was not altered after a meal, either liquid or solid, regular or high-fat diet, small or large meal, suggesting an absence of gastric-small intestinal reflex.

CONCLUSIONS

In type 2 diabetic rats, the regularity of intestinal slow waves is negatively correlated with the blood glucose level in both fasting and fed states. Diabetic rats exhibit a blunted postprandial response in intestinal slow waves compared with normal rats. There seems to be a lack of gastric-small intestinal reflex upon food ingestion in diabetic rats.

Progressive impairment in gastric and duodenal slow waves and autonomic function during progression of type 2 diabetes in rats

The abnormalities of gastrointestinal (GI) slow waves play key roles in the pathophysiology of diabetic gastroparesis, which is highly prevalent in type 2 diabetes (T2D). Although relatively well-investigated in diabetic enteric neuropathy, abnormalities and progressive impairments of gastric slow waves (GSWs) and duodenal slow waves (DSWs) are underinvestigated during the progression of T2D. The aim of this study was to explore alterations in GSW and DSW during the development of diabetes induced by high-fat diet (HFD) followed by a low dose of streptozotocin (STZ). Weekly recordings of slow waves from healthy, prediabetic to diabetes stages exhibited a progressively decreased percentage of normal slow waves (%NSW) starting after HFD feeding (prediabetic stage) in the fasting state and starting after STZ injection (diabetic stage) in the postprandial state. The postprandial increase in the power of slow waves observed in normal control rats was absent starting from 2 wk after HFD and persisted after STZ. The mechanism might be attributed to both progressively increased blood glucose (BG) and impaired autonomic function in view of the following results: 1) the %NSW was negatively correlated with the fasting BG; 2) during the oral glucose tolerance test, %NSW of DSW and BG exhibited a positive correlation in rats with hemoglobin A1C (HbA1C) < 5.0%, but a negative correlation in rats with HbA1C ≥ 5.0%; and 3) in comparison with baseline (healthy stage) of the same cohort, plasma pancreatic polypeptide (reflecting vagal activity) was progressively decreased, whereas plasma norepinephrine (reflecting sympathetic activity) was progressively increased.NEW & NOTEWORTHY This study recorded the progressive impairment in the regularity of gastric and duodenal slow waves in a rat model mimicking the progression to type 2 diabetes including the stage of health, prediabetic stage, and diabetes. The progressive impairment in gastric/duodenal slow waves might be attributed to the progressive increase in blood glucose and impairment in autonomic function.

Intestinal Electrical Stimulation Synchronized With Intestinal Slow Wave Ameliorates Glucagon-Induced Hyperglycemia in Rats

BACKGROUND

Synchronized intestinal electrical stimulation (SIES), in which intestinal electrical stimulation (IES) is delivered in synchronization with the intrinsic slow wave of small intestine, was previously reported to be more potent in accelerating small intestine transit than IES delivered at fixed frequency and phase. We hypothesized that SIES is more potent in suppressing postprandial blood glucose by enhancing the release of glucagon-like peptide-1 (GLP-1) and insulin.

MATERIALS AND METHODS

Rats underwent long-term implant of two pairs of electrodes at the duodenum for IES and SIES, respectively. Acute hyperglycemia was induced with glucagon, and the oral glucose tolerance test was performed on separate days with IES, SIES, or sham (no stimulation).

RESULTS

1. Glucagon reduced the percentage of normal slow wave in sham (70.9% ± 4.1%) from (84.9% ± 2.6%, p = 0.006) of control, which was ameliorated by SIES (82.5% ± 3.3%, p = 0.031). 2. IES and SIES reduced glucagon-induced increase of blood glucose (192 mg/dl) at 30 minutes by 17% and 20%, respectively. SIES showed a further inhibitory effect at 60 minutes (147 vs 171 mg/dl, p = 0.003, vs sham). 3. Compared with sham (139 pg/ml), GLP-1 at 30 minutes was increased in both IES (158 pg/ml) and SIES (169 pg/ml). GLP-1 level was still high at 60 minutes in rats with SIES. 4. At 30 minutes, the plasma insulin level was increased by 18.8 μIU/ml with SIES, which was significantly higher than that with sham (7.1 μIU/ml, p < 0.001) and IES (13.2 μIU/ml, p = 0.041).

CONCLUSION

SIES is more effective than IES in reducing glucagon-induced acute hyperglycemia by enhancing the release of GLP-1 and insulin.

Intestinal Electrical Stimulation Alters Hypothalamic Expression of Oxytocin and Orexin and Ameliorates Diet-Induced Obesity in Rats

BACKGROUND

Intestinal electrical stimulation (IES) has been proposed as a potential treatment for obesity. The aim of this study was to explore the central mechanism underlying the reduction of food intake and body weight by IES by studying the expression of anorexigenic- and orexigenic-peptide-containing neurons in the hypothalamus.

MATERIALS AND METHODS

Diet-induced obese (DIO) rats were divided into three groups to receive sham, IES, and pair-feeding for 4 weeks. Food intake was measured automatically and presented as daily and body weight measured weekly. The expressions of oxytocin, an anorexigenic neuropeptide, in the paraventricular nucleus of the hypothalamus (PVN) and the supraoptic nuclei of the hypothalamus (SON) and orexin-A, an orexigenic neuropeptide, in the lateral hypothalamic area (LHA) were studied using immunohistochemistry.

RESULTS

Compared with sham, IES reduced daily food intake by 28.3% at week 1, 35.6% at week 2, 15.6% at week 3, and 27.1% at week 4. Consistently, IES reduced body weight by 6.3%, compared with a weight gain of 7.2% in sham, and a slight weight loss of 0.5% in pair-feeding. Compared with sham, IES increased the expression of oxytocin-immunoreactive neurons in PVN and SON. Compared with sham, IES decreased the expression of orexin-immunoreactive neurons in LHA. Rats with pair-feeding also showed a relative decease in weight without any changes in the central hormones.

CONCLUSION

IES reduces food intake and body weight and improves glucose tolerance and insulin sensitivity in DIO rats. Its central mechanisms involve enhancement of anorexigenic peptides and suppression of orexigenic peptides in the hypothalamus.

Electronic Bypass for Diabetes: Optimization of Stimulation Parameters and Mechanisms of Glucagon-Like Peptide-1

OBJECTIVES

Intestinal electrical stimulation (IES) has been proposed for treating diabetes; however, its parameters need to be further systematically optimized. This study aimed to optimize the parameters of IES and investigate its possible mechanisms involving glucagon-like peptide-1 (GLP-1) in diabetic rats.

MATERIALS AND METHODS

Thirty-six high-fat diet-induced diabetic rats were chronically implanted with a pair of bipolar electrodes at the duodenum for IES. The oral glucose tolerance test (OGTT) was performed in a number of sessions with IES using different parameters and biphasic charge-balanced waveforms to derive the best values for train on-time, pulse frequency, and pulse width. Incretin hormones such as GLP-1 were assessed and the GLP-1 antagonist Exendin 9-39 was used to assess the role of GLP-1 in the ameliorating effect of IES on hyperglycemia.

RESULTS

The most effective IES parameters in reducing blood glucose (BG) during the OGTT were derived: 1.2 sec on, 0.3 sec off, 80 Hz, 3 msec. IES with these parameters reduced BG level by at least 29% from 15 min to 180 min (p < 0.05 for all points, N = 10). IES with these stimulation parameters increased plasma GLP-1 level at 30 min, 60 min, 90 min and gastric inhibitory peptide (GIP) level at 30 min (N = 8). Exendin 9-39 blocked the inhibitory effect of IES on BG (p > 0.05, IES + Exendin 9-39 vs. sham-IES, N = 8).

CONCLUSION

IES with the most effective parameters derived in this study improves hyperglycemia in diabetic rats. The ameliorating effect of IES on hyperglycemia is attributed to the enhanced release of GLP-1. IES has great potential for treating diabetes.

Intestinal Electrical Stimulation Enhances Release of Postprandial Incretin Hormones Via Cholinergic Mechanisms

INTRODUCTION

Intestinal electrical stimulation (IES) has been reported to reduce body weight and improve glucose tolerance in obese and diabetic rats. Our study aimed to investigate possible IES mechanisms involving incretin hormones using intraduodenal glucose infusion in rats. We hypothesized that the enhanced release of postprandial glucagon-like peptide-1 (GLP-1) at early phase by IES was mediated through neuro/paracrine mechanisms involving the vagal nerve and glucose-dependent insulinotropic peptide (GIP).

METHODS

Fifteen normal male Sprague-Dawley rats chronically implanted with duodenal electrodes for IES, and an intra-duodenum catheter for the infusion of glucose were studied in a series of sessions with IES of different parameters with and without atropine and M3 receptor antagonist. Blood samples were collected via the tail vein for the measurement of blood glucose, and plasma GLP-1, and GIP.

RESULTS

(1) Compared to sham-IES, IES of 0.3 ms reduced blood glucose by 16.5-28.4% between 30 and 120 min (all time points p < 0.05), and IES of 3-ms reduced blood glucose at 60 (12.6%) and 90 min (11.8%). IES of 0.3 ms showed a greater hypoglycemic effect than 3 ms (p = 0.024) at 30 min. (2) IES elevated plasma GLP-1 with 0.3 ms (p = 0.001) and with 3 ms p = 0.03). (3) IES substantially elevated plasma GIP with 0.3 ms (p = 0.002) and with 3 ms (p < 0.001). (4) Pretreatment of atropine and the M3 receptor antagonist 4-DAMP blocked the effects of IES on GLP-1, GIP, and blood glucose.

CONCLUSIONS

IES reduces postprandial blood glucose by enhancing the release of GLP-1 and GIP mediated via the cholinergic mechanism.

Characteristics of myoelectrical activities along the small intestine and their responses to test meals of different glycemic index in rats

The purpose of this study was to characterize intestinal myoelectrical activity along the small intestine and investigate its responses to test meals with different glycemic index at different locations. Sixteen rats were implanted with electrodes in the serosal surface of the duodenum, jejunum, and ileum. Intestinal myoelectrical activities were recorded from these electrodes for 30 min in the fasting state and 3 h after four kinds of meals with different glycemic index, together with the assessment of blood glucose. The results were as follows: 1) in the fasting state, the percentage of normal intestinal slow waves (%NISW) showed no difference; however, the dominant frequency (DF), power (DP), and percentage of spike activity superimposed on the intestinal slow wave (NS/M) were progressively decreased along the entire small intestine; 2) regular solid meal and Ensure solicited no changes in any parameters of intestinal myoelectrical activity; whereas glucose and glucose + glucagon significantly altered the %NISW, DF, DP, and NS/M, and the effects on the proximal intestine were opposite to those in the distal intestine; and 3) postprandial blood glucose level was significantly correlated with %NISW along the entire small intestine. We found that that, in addition to the well-known frequency gradient, there is also a gradual decrease in the DP and spikes along the small intestine in the fasting state. Glucose and hyperglycemic meals inhibit myoelectrical activities in the proximal small intestine but result in enhanced but more dysrhythmic intestinal myoelectrical activities. There is a significant negative correlation between the normality of intestinal slow waves and blood glucose.

Hypoglycemic Effects of Intestinal Electrical Stimulation by Enhancing Nutrient-Stimulated Secretion of GLP-1 in Rats

PURPOSE

To find out the best location for intestinal electrical stimulation (IES) to decrease hyperglycemia, and mechanisms involving intraluminal nutrients and plasma glucagon-like peptide-1 (GLP-1) MATERIALS AND METHODS: Eight rats had electrodes implanted at the duodenum and ileums for IES. The oral glucose tolerance test (OGTT) was performed with IES and sham-IES and with/without GLP-1 antagonist, exendin. To study the role of intraluminal nutrients, the experiment was repeated using intraperitoneal glucose tolerance test (IPGTT). Glucagon was administrated in the OGTT/IPGTT to induce temporary hyperglycemia.

RESULTS

(1) In the OGTT, IES at the duodenum reduced blood glucose from 30 to 120 min after oral glucose (P < 0.05, vs. sham-IES) and the hypoglycemic effect was more potent than IES at the ileum. (2) The hypoglycemic effect of IES was absent in IPGTT experiment, suggesting the important role of intraluminal nutrients. (3) An increase in GLP-1 was noted in the OGTT with IES at the duodenum in comparison with sham-IES. Moreover, the blocking effect of exendin suggested the role of GLP-1 in the hypoglycemic effect of IES.

CONCLUSIONS

The best stimulation location for IES to decrease hyperglycemia is in the duodenum. The hypoglycemic effect of IES is attributed to the enhancement in nutrient-stimulated release of GLP-1.

Electroacupuncture via chronically implanted electrodes improves gastric dysmotility mediated by autonomic-cholinergic mechanisms in a rodent model of functional dyspepsia

BACKGROUND

Electroacupuncture (EA) has been shown to be effective in reducing symptoms in patients with functional dyspepsia (FD). However, its mechanisms remain largely unknown. The aim of this study was to investigate mechanisms of the prokinetic effects of EA in a rodent model of FD.

METHODS

A FD model was established by neonatal treatment of iodoacetamide (IA). Eight weeks later, the rats were implanted with electrodes in the stomach for the measurement of gastric slow waves (GSW) and electrodes into acupoints ST36 for EA. Autonomic functions were assessed by the spectral analysis of heart rate variability.

KEY RESULTS

(i) The IA-treated rats ("FD" rats) showed increased dysrhythmia in both fasting and fed states (P < .01) as well as during rectal distention (P < .02). EA reduced the percentage of dysrhythmia (P < .05 for both fasting and fed) and normalized RD-induced impairment in GSW in "FD" rats. Atropine blocked the effect of EA on GSW. (ii) "FD" rats showed delayed gastric emptying (P = .001 vs control) that was accelerated with EA (P = .01, vs sham-EA). (iii) "FD" rats showed increased plasma norepinephrine (P = .006, vs control) that was suppressed with EA (P = .003) and reduced vagal activity that was improved with EA.

CONCLUSIONS AND INFERENCES

Gastric motility (GSW and GE) is impaired in rats treated with IA, possibly attributed to impaired autonomic functions. EA improves GSW and accelerates GE mediated via the autonomic and cholinergic mechanisms.