Morphologic diversity of the minor salivary glands of the rat: fertile ground for studies in gene function and proteomics

In this article the locations and histologic and ultrastructural features of all of the minor salivary glands of the rat are presented; similarities and differences among them are highlighted. These glands are almost as diverse morphologically as the major salivary glands of the rat. The acini of von Ebner's glands are serous; those of the anterior and posterior buccal glands and minor sublingual glands are mucous; and those of the glossopalatal, palatal, and Weber's glands are mucous with serous demilunes. The anterior buccal, minor sublingual and von Ebner's glands have striated and stratified columnar ducts, while only the minor sublingual and von Ebner's glands have intercalated ducts. The glossopalatal, palatal, posterior buccal and Weber's glands have none of these ducts; the tubulo-acini drain abruptly into short terminal ducts composed of stratified squamous epithelium. All of the mucous acini react with an antibody to a mucin (Muc19) of the rat major sublingual gland, but in some of the glands the reaction varies in intensity among the acinar cells. Ultrastructurally, the mucous secretory granules of the anterior buccal, glossopalatal, palatal and Weber's glands are biphasic, while those of the minor sublingual and posterior buccal glands are monophasic. Although there is a considerable body of literature concerning the development, innervation, physiology and proteomics of von Ebner's glands, investigation of the other minor salivary glands of the rat ranges from modest to nearly nonexistent.     

Hyperglycemia-induced GLP-1R downregulation causes RPE cell apoptosis

Glucagon-like peptide-1 receptor (GLP-1R) is closely associated with the onset of diabetes and its complications. However, its roles in diabetic retinopathy are unknown. Retinal pigment epithelial (RPE) cells are a crucial component of the outer blood–retina barrier and their death is related to the progression of diabetic retinopathy. Thus, we examined the pathophysiological role of GLP-1R in RPE cell apoptosis. We found that GLP-1R expression was lower in the isolated neuroretina and RPE cells of streptozotocin-treated rats than in vehicle-treated rats. High-glucose treatment also decreased GLP-1R expression in a human RPE cell line (ARPE-19 cells). GLP-1R was silenced in ARPE-19 cells, in order to elucidate the pathophysiological roles of GLP-1R. This increased intracellular reactive oxygen species (ROS) generation and activated p53-mediated Bax promoter and endoplasmic reticulum (ER) stress signaling. We also found that GLP-1R knockdown-mediated p53 expression was regulated by ER stress. Interestingly, antioxidant treatment and peroxiredoxin 1 (Prx1) overexpression attenuated GLP-1R knockdown-induced ER stress signaling and p53 expression. Finally, to confirm that GLP-1R activation has protective effects, ARPE-19 cells were treated with exendin-4, a synthetic GLP-1R agonist. This attenuated high-glucose-induced ROS generation, ER stress signaling, and p53 expression. Collectively, these results indicated that hyperglycemia decreases GLP-1R expression in RPE cells. Such a decrease generates intracellular ROS, which increases ER stress-mediated p53 expression, and subsequently causes apoptosis by increasing Bax promoter activity. Our data suggested that regulation of GLP-1R expression is a promising approach for the treatment of diabetic retinopathy.     

下丘脑室旁核注射GLP-1 对糖尿病大鼠中枢GLP-1 受体表达

目的:探讨下丘脑室旁核(hypothalamic paraventricular nucleus,PVN)注射GLP-1(胰高血糖素样肽-1)对糖尿病大鼠胃排空的影响及机制。方法:30只Wistar大鼠随机分为正常对照组(NC组)、糖尿病组(DM组)和GLP-1干预组(GLP-1组),每组各10只。DM组和GLP-1组腹腔注射链脲佐菌素,三组大鼠均PVN区埋置套管,恢复7d,GLP-1组微量注射0.5μg/0.5μl的GLP-1,NC组和DM组大鼠PVN区微量注射等体积生理盐水。甲基纤维素-酚红灌胃法检测胃排空;半定量RT-PCR检测大鼠下丘脑GLP-1RmRNA的表达。结果:DM组胃排空率较NC组明显升高(P<0.05),GLP-1组胃排空明显低于DM组(P<0.05),GLP-1组和NC组差异无统计学意义(P>0.05)。GLP-1组下丘脑GLP-1RmRNA的表达明显高于DM组和NC组(P<0.05),并与胃排空率成负相关(P<0.05)。DM组和NC组差异无统计学意义(P>0.05)。结论:PVN区注射GLP-1可以抑制糖尿病大鼠早期胃排空加速,作用机制可能和促进下丘脑GLP-1受体表达有关。     

Effects of Selenium and Exendin-4 on Glucagon-Like Peptide-1 Receptor, IRS-1, and Raf-1 in the Liver of Diabetic Rats

Selenium and exendin-4 exert antidiabetic effects by unknown mechanisms. Herein, we investigated their effects on the expression of glucagon-like peptide-1 receptor (GLP-1R), insulin receptor substrate-1 (IRS-1), and Raf-1 in the livers of rats with streptozotocin-induced diabetes. Diabetic rats were injected intraperitoneally with exendin-4 (0.03?μg/kg body weight) twice daily or treated with 5?ppm selenium as sodium selenite in drinking water for 4?weeks. Both selenium and exendin-4 reduced the hyperglycemia in diabetic rats. Induction of diabetes mellitus resulted in decreased level of GLP-1R and increased levels of IRS-1 and Raf-1 in the liver. Treatment of diabetic rats with selenium or exendin-4 resulted in increased level of GLP-1R and decreased levels of IRS-1 and Raf-1 in the liver, compared with the levels in diabetic rats. Therefore, the antidiabetic actions of selenium and exendin-4 involve their effects on GLP-1R, IRS-1, and Raf-1 levels in the liver.     

High-Level Expression of Fusion Protein Containing 10 Tandem Repeated GLP-1 Analogs in Yeast Pichia pastoris and Its Biological Activity in a Diabetic Rat Model

Glucagon-like peptide-1 (GLP-1), an incretin secreted by intestinal L-cells, can effectively lower blood glucose levels in patients with diabetes. A fusion gene, consisting of 10 tandem repeated GLP-1 analog genes, was expressed at a high level in the yeast Pichia pastoris. SDS polyacrylamide gel electrophoresis (SDS–PAGE), and Western Blotting results showed that fusion protein migrated as a single protein band with a molecular weight of 36 kDa. A biological activity test showed that the GLP-1 analog could significantly lower the level of serum glucose when GLP-1 purified analog was injected into diabetic rats. A potential strategy for large-scale production of fusion protein containing the 10 GLP-1 analogs as discovered, and a single GLP-1 analog was obtained from fusion protein digested with trypsin. This should be inspired foreign expression of medicinal short peptides and be valuable in further research on GLP-1 analog drugs in the treatment of diabetes mellitus.     

Duodenal-jejunal bypass protects GK rats from {beta}-cell loss and aggravation of hyperglycemia and increases enteroendocrine cells coexpressing GIP and GLP-1

Dramatic improvement of type 2 diabetes is commonly observed after bariatric surgery. However, the mechanisms behind the alterations in glucose homeostasis are still elusive. We examined the effect of duodenal-jejunal bypass (DJB), which maintains the gastric volume intact while bypassing the entire duodenum and the proximal jejunum, on glycemic control, β-cell mass, islet morphology, and changes in enteroendocrine cell populations in nonobese diabetic Goto-Kakizaki (GK) rats and nondiabetic control Wistar rats. We performed DJB or sham surgery in GK and Wistar rats. Blood glucose levels and glucose tolerance were monitored, and the plasma insulin, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) levels were measured. β-Cell area, islet fibrosis, intestinal morphology, and the density of enteroendocrine cells expressing GLP-1 and/or GIP were quantified. Improved postprandial glycemia was observed from 3 mo after DJB in diabetic GK rats, persisting until 12 mo after surgery. Compared with the sham-GK rats, the DJB-GK rats had an increased β-cell area and a decreased islet fibrosis, increased insulin secretion with increased GLP-1 secretion in response to a mixed meal, and an increased population of cells coexpressing GIP and GLP-1 in the jejunum anastomosed to the stomach. In contrast, DJB impaired glucose tolerance in nondiabetic Wistar rats. In conclusion, although DJB worsens glucose homeostasis in normal nondiabetic Wistar rats, it can prevent long-term aggravation of glucose homeostasis in diabetic GK rats in association with changes in intestinal enteroendocrine cell populations, increased GLP-1 production, and reduced β-cell deterioration.     

Histochemical Phenotypes of Von Ebner's Gland of Ferret and their Functional Implications

Von Ebner's gland of ferret was examined by means of light microscopy, protein, mucosubstance and enzyme histochemistry, and neurohistology. Acinar cells were replete with granules containing neutral mucosubstances and disulphides, and showed strong diffuse acid phosphatase activity and weak granular staining for peroxidase. Staining for cytochrome oxidase, succinate dehydrogenase, and NADH and NAD(P)H dehydrogenases was also seen. Basolateral plasmalemma of acinar cells showed weak, ouabain-sensitive Na⁺,K⁺-ATPase activity. Ductal cells were of a simple appearance, contained thiols and showed variable staining for acid phosphatase, dehydrogenases and cytochrome oxidase. Variable amounts of β-glucuronidase reaction product were localized in the glandular parenchyma, being marked in atrophic areas. Prominent stellate myoepithelial cells embracing acini and also basal ductal cells were demonstrated by alkaline phosphatase. Thiamine pyrophosphatase reaction product was concentrated in blood vessels around parenchyma, with little Golgi-like staining in acinar cells. Acetylcholinesterase activity was associated with an extensive network of nerve fibres embracing parenchyma, whereas catecholamine fluorescence was not seen. The results suggest that the acini of von Ebner's gland of ferret synthesise neutral secretory glycoproteins and peroxidase. Water mobilization is inconspicuous. Lysosomal activities feature in the parenchyma, possibly a consequence of processing secretory products in acini, absorption in ducts and/or adaptation atrophy. The gland receives a rich cholinergic-type innervation, and has extensive myoepithelial and microvascularbreak networks.     

Effects of exendin-4 and selenium on the expression of GLP-1R,IRS-1, and preproinsulin in the pancreas of diabetic rats

The mechanisms by which exendin-4 and selenium exert their antidiabetic actions are still unclear. Here, we investigated the effects of exendin-4 or selenium administration on the expression of glucagon-like peptide-1 receptor (GLP-1R), insulin receptor substrate-1 (IRS-1), and preproinsulin in the pancreas of diabetic rats. Diabetes was induced by streptozotocin administration. Diabetic rats were injected intraperitoneally with 0.03 μg exendin-4/kg body weight/daily or treated with 5 ppm selenium in drinking water for a period of 4 weeks. GLP-1R and IRS-1 levels were decreased while the level of preproinsulin messenger RNA (mRNA) was increased in the pancreas of diabetic untreated rats, as compared to that in control rats. Treatment of diabetic rats with exendin-4 increased protein and mRNA levels of GLP-1R, and IRS-1, and the mRNA level of preproinsulin in the pancreas, as compared to their levels in diabetic untreated rats. Selenium treatment of diabetic rats increased the pancreatic mRNA levels of GLP-1R, IRS-1, and preproinsulin. Exendin-4 or selenium treatment of diabetic rats also increased the numbers of pancreatic islets and GLP-1R molecules in the pancreas. Therefore, exendin-4 and selenium may exert their antidiabetic effects by increasing GLP-1R, IRS-1, and preproinsulin expression in the pancreas and by increasing the number of pancreatic islets.     

The quest for the sea urchin egg receptor for sperm

The incretin glucagon-like peptide-1 (GLP-1) and other GLP-1 receptor agonists have been shown to cause both antiapoptotic as well as regenerative effects on beta-cells in different animal models for diabetes. Our aim of this study was to test the hypothesis that spontaneously diabetic non obese diabetic (NOD) mice show an altered expression of GLP-1 compared to normoglycemic age-matched controls as a consequence of a diabetic state. To do this we used an ELISA prototype for mouse GLP-1 to measure plasma total GLP-1 from recently diabetic NOD mice as well as from age-matched normoglycemic NOD mice (controls). We also stained sections of pancreatic glands for GLP-1 from diabetic NOD mice and controls. We found increased levels of plasma total GLP-1 in diabetic NOD mice, when compared to control mice, both from non-fasted mice and from mice fasted for 2h. Furthermore, diabetic NOD mice displayed a higher GLP-1 response to an oral glucose tolerance test, compared to control mice. We also found that sections of pancreatic glands from diabetic NOD mice had an increased GLP-1 positive islet area in regard to relative islet area (i.e. total islet area / total pancreas area of the sections) compared to control mice. To our knowledge, this study is the first to show increased levels of GLP-1 in plasma in spontaneously diabetic NOD mice. We suggest that these results might represent a compensatory mechanism of the diabetic NOD mice to counteract beta-cell loss and hyperglycemia.     

High-level expression of fusion protein containing 10 tandem repeated GLP-1 analogs in yeast Pichia pastoris and its biological activity in a diabetic rat model

Glucagon-like peptide-1 (GLP-1), an incretin secreted by intestinal L-cells, can effectively lower blood glucose levels in patients with diabetes. A fusion gene, consisting of 10 tandem repeated GLP-1 analog genes, was expressed at a high level in the yeast Pichia pastoris. SDS polyacrylamide gel electrophoresis (SDS-PAGE), and Western Blotting results showed that fusion protein migrated as a single protein band with a molecular weight of 36 kDa. A biological activity test showed that the GLP-1 analog could significantly lower the level of serum glucose when GLP-1 purified analog was injected into diabetic rats. A potential strategy for large-scale production of fusion protein containing the 10 GLP-1 analogs as discovered, and a single GLP-1 analog was obtained from fusion protein digested with trypsin. This should be inspired foreign expression of medicinal short peptides and be valuable in further research on GLP-1 analog drugs in the treatment of diabetes mellitus.     

室旁核注射胰高血糖素样肽-1对不同病程糖尿病大鼠胃排空的影响（英文）

目的：研究下丘脑室旁核（paraventricular nucleus,PVN）注射胰高血糖素样肽-1（GLP-1）对糖尿病早期大鼠胃排空的影响,并探讨其相关作用机制。方法：60只清洁级雄性Wistar大鼠随机分为正常对照组（NC组）,糖尿病组（DM组）,GLP-1干预组（GLP-1组）,每组各20只,后两组腹腔注射链脲佐菌素（STZ）制备糖尿病模型,分别于注射STZ2周、6周后每组随机取半数进行实验,实验前于无菌条件下大鼠一侧下丘脑PVN区埋置套管,GLP-1组经套管注入GLP-1,NC组及DM组注入等体积生理盐水。酚红灌胃法检测胃排空率,酶联免疫吸附法（ELISA）测定血浆GLP-1浓度,半定量RT-PCR法测定胃窦、胃底GLP-1RmRNA表达。结果：注射STZ 2周后,DM组较NC组胃排空率显著升高（P〈0.01）。GLP-1组胃排空率低于DM组（P〈0.01）,血浆GLP-1浓度高于DM组及NC组（P均〈0.05）,胃窦GLP-1RmRNA表达明显高于DM组、NC组（P均〈0.01）。注射STZ 6周后,DM组胃排空率高于NC组（P〈0.01）。GLP-1组较DM组胃排空率显著降低（P〈0.01）,血浆GLP-1浓度、胃窦GLP-1RmRNA表达显著高于DM组、NC组（P均〈0.01）。结论：下丘脑PVN区注射GLP-1后,可减慢糖尿病大鼠初期加速的胃排空,原因可能与血浆GLP-1浓度及胃窦GLP-1RmRNA表达增加有关。     

Role of glucagon-like peptide-1 and its agonists on early prevention of cardiac remodeling in type 1 diabetic rat hearts

Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted from intestinal L cells upon nutrients ingestion, and is currently used for treating diabetes mellitus. It plays an important role in receptor modulation and cross talk with insulin at the coronary endothelium (CE) and cardiomyocytes (CM) in diabetic type 1 rat heart model. We studied the effects of insulin, GLP-1 analogues (exendin-4), and dipeptidyl peptidase-IV (DPP-IV) inhibitor on GLP-1 cardiac receptor modulation. The binding affinity of GLP-1 to its receptor on CE and CM was calculated using a rat heart perfusion model with [(125)I]-GLP-1(7-36). Tissue samples from the heart were used for immunostaining and Western blot analyses. GLP-1 systemic blood levels were measured using ELISA. GLP-1 binding affinity (τ) increased on the CE (0.33 ± 0.01 vs. 0.25 ± 0.01 min; p < 0.001) and decreased on the CM (0.29 ± 0.02 vs. 0.43 ± 0.02 min; p < 0.001) in the diabetic non-treated rats when compared to normal. There was normalization of τ back to baseline on the CE and CM levels with insulin and DPP-IV inhibitor treatment, respectively. Histological sections and immunofluorescence showed receptor up-regulation in diabetic rats with significant decrease and even normalization with the different treatment strategies. Systemic GLP-1 levels increased after 14 days of diabetes induction (10 ± 3.7 vs. 103 ± 58 pM; p = 0.0005). In conclusion, there is a significant GLP-1 receptor affinity modulation on the CE and CM levels in rats with diabetes type 1, and a cross talk with GLP-1 analogues in early prevention of cardiac remodeling.     

Excessive islet NO generation in type 2 diabetic GK rats coincides with abnormal hormone secretion and is counteracted by GLP-1

Background

A distinctive feature of type 2 diabetes is inability of insulin-secreting β-cells to properly respond to elevated glucose eventually leading to β-cell failure. We have hypothesized that an abnormally increased NO production in the pancreatic islets might be an important factor in the pathogenesis of β-cell dysfunction.

Principal Findings

We show now that islets of type 2 spontaneous diabetes in GK rats display excessive NO generation associated with abnormal iNOS expression in insulin and glucagon cells, increased ncNOS activity, impaired glucose-stimulated insulin release, glucagon hypersecretion, and impaired glucose-induced glucagon suppression. Pharmacological blockade of islet NO production by the NOS inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) greatly improved hormone secretion from GK islets suggesting islet NOS activity being an important target to inactivate for amelioration of islet cell function. The incretin hormone GLP-1, which is used in clinical practice suppressed iNOS and ncNOS expression and activity with almost full restoration of insulin release and partial restoration of glucagon release. GLP-1 suppression of iNOS expression was reversed by PKA inhibition but unaffected by the proteasome inhibitor MG132. Injection of glucose plus GLP-1 in the diabetic rats showed that GLP-1 amplified the insulin response but induced a transient increase and then a poor depression of glucagon.

Conclusion

The results suggest that abnormally increased NO production within islet cells is a significant player in the pathogenesis of type 2 diabetes being counteracted by GLP-1 through PKA-dependent, nonproteasomal mechanisms.     

The effect of glucagon-like peptide-1 in the management of diabetes mellitus: cellular and molecular mechanisms

Incretins, such as glucagon-like peptide-1 (GLP)-1, have been shown to elevate plasma insulin concentration. The purpose of this study is to investigate the cellular and molecular basis of the beneficial effects of GLP-1. Normal and diabetic male Wistar rats were treated with GLP-1 (50 ng/kg body weight) for 10 weeks. At the end of the experiment, pancreatic tissues were taken for immunohistochemistry, immunoelectron microscopy and real-time polymerase chain reaction studies. Samples of blood were retrieved from the animals for the measurement of enzymes and insulin. The results show that treatment of diabetic rats with GLP-1 caused significant (P?GLP-1 (10^?12–10^?6 M) induced significant (P?GLP-1-treated rats compared to controls. GLP-1 treatment induced significant (P?GLP-1-receptor genes in diabetic animals compared to controls. GLP-1 is present in pancreatic beta cells and significantly (P?GLP-1 is co-localized with insulin and seems to exert its beneficial effects by increasing cellular concentrations of endogenous antioxidant genes and other genes involved in the maintenance of pancreatic beta cell structure and function.     

Enhanced effect of daytime restricted feeding on the circadian rhythm of streptozotocin-induced type 2 diabetic rats

There is increasing awareness of the link between impaired circadian clocks and multiple metabolic diseases. However, the impairment of the circadian clock by type 2 diabetes has not been fully elucidated. To understand whether and how the function of circadian clock is impaired under the diabetic condition, we examined not only the expression of circadian genes in the heart and pineal gland but also the behavioral rhythm of type 2 diabetic and control rats in both the nighttime restricted feeding (NRF) and daytime restricted feeding (DRF) conditions. In the NRF condition, the circadian expression of clock genes in the heart and pineal gland was conserved in the diabetic rats, being similar to that in the control rats. DRF shifted the circadian phases of peripheral clock genes more efficiently in the diabetic rats than those in the control rats. Moreover, the activity rhythm of rats in the diabetic group was completely shifted from the dark phase to the light phase after 5 days of DRF treatment, whereas the activity rhythm of rats in the control group was still under the control of the suprachiasmatic nucleus (SCN) after the same DRF treatment. Furthermore, the serum glucose rhythm of type 2 diabetic rats was also shifted and controlled by the external feeding schedule, ignoring the SCN rhythm. Therefore, DRF shows stronger effect on the reentrainment of circadian rhythm in the type 2 diabetic rats, suggesting that the circadian system in diabetes is unstable and more easily shifted by feeding stimuli.     

Exenatide does not evoke pancreatitis and attenuates chemically induced pancreatitis in normal and diabetic rodents

The risk of developing pancreatitis is elevated in type 2 diabetes and obesity. Cases of pancreatitis have been reported in type 2 diabetes patients treated with GLP-1 (GLP-1R) receptor agonists. To examine whether the GLP-1R agonist exenatide potentially induces or modulates pancreatitis, the effect of exenatide was evaluated in normal or diabetic rodents. Normal and diabetic rats received a single exenatide dose (0.072, 0.24, and 0.72 nmol/kg) or vehicle. Diabetic ob/ob or HF-STZ mice were infused with exenatide (1.2 and 7.2 nmol·kg(-1)·day(-1)) or vehicle for 4 wk. Post-exenatide treatment, pancreatitis was induced with caerulein (CRN) or sodium taurocholate (ST), and changes in plasma amylase and lipase were measured. In ob/ob mice, plasma cytokines (IL-1β, IL-2, IL-6, MCP-1, IFNγ, and TNFα) and pancreatitis-associated genes were assessed. Pancreata were weighed and examined histologically. Exenatide treatment alone did not modify plasma amylase or lipase in any models tested. Exenatide attenuated CRN-induced release of amylase and lipase in normal rats and ob/ob mice but did not modify the response to ST infusion. Plasma cytokines and pancreatic weight were unaffected by exenatide. Exenatide upregulated Reg3b but not Il6, Ccl2, Nfkb1, or Vamp8 expression. Histological analysis revealed that the highest doses of exenatide decreased CRN- or ST-induced acute inflammation, vacuolation, and acinar single cell necrosis in mice and rats, respectively. Ductal cell proliferation rates were low and similar across all groups of ob/ob mice. In conclusion, exenatide did not modify plasma amylase and lipase concentrations in rodents without pancreatitis and improved chemically induced pancreatitis in normal and diabetic rodents.     

C-Fos在db/db自发性糖尿病小鼠颌下腺的表达

目的观察转基因糖尿病小鼠下颌下腺形态学改变与原癌基因C-fos蛋白表达的关系,为糖尿病的临床及基础研究提供依据。方法引进日本C57BL/ksj-db/ m表型正常隐性基因小鼠,其近亲交配所得纯合子后代,即为db/db(单基因遗传自然发病型)糖尿病小鼠。取3、4、6、8、10月龄db/db糖尿病小鼠及相应月龄的db/ m正常小鼠下颌下腺,行HE染色及SP免疫组化染色后进行图象分析,统计各组下颌下腺C-fos阳性表达的细胞数,观察其形态学改变。结果糖尿病小鼠下颌下腺腺泡萎缩,细胞缩小,形态不规则,排列不整齐。各月龄糖尿病小鼠颌下腺C-Fos阳性细胞明显低于相应对照组(P<0.01),且逐渐减少,呈下降趋势。结论db/db糖尿病状态下颌下腺细胞表达C-Fos蛋白明显降低,c-fos低表达可能与下颌下腺实质细胞的增殖减弱性形态学变化密切相关。     

The combination of colesevelam with sitagliptin enhances glycemic control in diabetic ZDF rat model

Bile acid sequestrants have been shown to reduce glucose levels in patients with type 2 diabetes. We previously reported that the bile acid sequestrant colesevelam HCl (Welchol) (COL) induced the release of glucagon-like peptide (GLP)-1 and improved glycemic control in insulin-resistant rats. In the present study, we tested whether adding sitagliptin (Januvia) (SIT), which prolongs bioactive GLP-1 half life, to COL would further enhance glycemic control. Male Zucker diabetic fatty (ZDF) rats were assigned to four groups: diabetic model without treatment (the model), the model treated with 2% COL or 0.4% (120 mg/day) SIT alone, or with the combination (COL+SIT). After 4 wk of treatment, the glucose area under the curve (AUC) was reduced more in the COL+SIT than the COL although both groups showed decreased glucose AUC with increased AUC of bioactive GLP-1 (GLP-1A) compared with the model group. The above changes were not observed after 8 wk. Increasing the SIT dose by 50% (180 mg SIT/day) in the diet reduced the glucose AUC in the COL+SIT group even after 8 wk but still not in the SIT alone group compared with the model. It was noteworthy that, after 8 wk, insulin levels in the SIT group declined to levels similar to the model. Histological examination of the pancreatic β-cell islets showed that islet sizes were larger, proliferation enhanced, and cell apoptosis reduced in the COL+SIT but not the SIT alone group compared with the model. We hypothesize that the combination of COL with SIT extends the half life of COL-induced GLP-1A and benefits preservation of the islets that delay the development of diabetes and improve glycemic control. This study suggests that the combined therapy (COL+SIT) is more effective than either drug alone for reducing glucose levels in diabetes.