Effects of insulin therapy on weight gain and fat distribution in the HF/HS-STZ rat model of type 2 diabetes.

BACKGROUND/OBJECTIVES: Insulin therapy is required for many patients with the obesity-related disorder type 2 diabetes, but is also associated with weight gain. The specific location of adipose tissue location matters to cardiovascular disease (CVD) risk. We investigated effects of exogenous insulin on fat distribution in the high-fat/high-sucrose fed rat treated with streptozotocin (HF/HS-STZ) rat model of type 2 diabetes. We also examined effects of insulin therapy on circulating CVD markers, including adiponectin, triglycerides (TGs), total cholesterol and high-density lipoprotein. SUBJECTS/METHODS: Male SD rats were HF/HS fed for 5 weeks followed by STZ treatment to mimic the hallmarks of human obesity-associated insulin resistance followed by hyperglycemia. Magnetic resonance imaging and computed tomography were used to determine total fat, abdominal fat distribution and liver fat before and after insulin therapy in HF/HS-STZ rats. HbA1c%, TGs, cholesterol, high-density lipoprotein and adiponectin were analyzed by conventional methods adapted for rats. RESULTS: Insulin therapy lowered HbA1c (P<0.001), increased body weight (P<0.001), increased lean mass (P<0.001) and led to a near doubling of total fat mass (P<0.001), with the highest increase in subcutaneous adipose tissue as compared with visceral adipose tissue (P<0.001). No changes in liver fat were observed after insulin therapy, whereas plasma TG and cholesterol levels were decreased (P<0.001, P<0.01), while high-density lipoprotein (HDL) and adiponectin levels were elevated (P<0.01, P<0.001). CONCLUSIONS: Using the HF/HS-STZ rat as an animal model for type 2 diabetes, we find that insulin therapy modulates fat distribution. Specifically, our data show that insulin has a relatively positive effect on CVD-associated parameters, including abdominal fat distribution, lean body mass, adiponectin, TGs and HDL in HF/HS-STZ rats, despite a modest gain in weight.

Upregulation of alpha cell glucagon-like peptide 1 (GLP-1) in Psammomys obesus--an adaptive response to hyperglycaemia?

AIMS/HYPOTHESIS: The hormone glucagon-like peptide 1 (GLP-1) is released in response to a meal from the intestinal L-cells, where it is processed from proglucagon by the proconvertase (PC)1/3. In contrast, in the adult islets proglucagon is processed to glucagon by the PC2 enzyme. The aim of the study was to evaluate if, during the development of diabetes, alpha cells produce GLP-1 that, in turn, might trigger beta cell growth. METHODS: Beta cell mass, GLP-1 and insulin levels were measured in the gerbil Psammomys obesus (P. obesus), a rodent model of nutritionally induced diabetes. Furthermore, the presence of biologically active forms of GLP-1 and PC1/3 in alpha cells was demonstrated by immunofluorescence, and the release of GLP-1 from isolated P. obesus, mouse and human islets was investigated. RESULTS: During the development of diabetes in P. obesus, a significant increase in GLP-1 was detected in the portal vein (9.8 ± 1.5 vs 4.3 ± 0.7 pmol/l, p < 0.05), and in pancreas extracts (11.4 ± 2.2 vs 5.1 ± 1.3 pmol/g tissue, p < 0.05). Freshly isolated islets from hyperglycaemic animals released more GLP-1 following 24 h culture than islets from control animals (28.2 ± 4.4 pmol/l vs 5.8 ± 2.4, p < 0.01). GLP-1 release was increased from healthy P. obesus islets following culture in high glucose for 6 days (91 ± 9.1 pmol/l vs 28.8 ± 6.6, p < 0.01). High levels of GLP-1 were also found to be released from human islets. PC1/3 colocalised weakly with alpha cells. CONCLUSIONS/INTERPRETATION: GLP-1 release from alpha cells is upregulated in P. obesus during the development of diabetes. A similar response is seen in islets exposed to high glucose, which supports the hypothesis that GLP-1 released from alpha cells promotes an increase in beta cell mass and function during metabolic challenge such as diabetes.

Quality of plasma sampled by different methods for multiple blood sampling in mice.

For oral glucose tolerance test (OGTT) in mice, multiple blood samples need to be taken within a few hours from conscious mice. Today, a number of essential parameters may be analysed on very small amounts of plasma, thus reducing the number of animals to be used. It is, however, crucial to obtain high-quality plasma or serum in order to avoid increased data variation and thereby increased group sizes. The aim of this study was to find the most valid and reproducible method for withdrawal of blood samples when performing OGTT. Four methods, i.e. amputation of the tail tip, lateral tail incision, puncture of the tail tip and periorbital puncture, were selected for testing at 21 degrees C and 30 degrees C after a pilot study. For each method, four blood samples were drawn from C57BL/6 mice at 30 min intervals. The presence of clots was registered, haemolysis was monitored spectrophotometrically at 430 nm, and it was noted whether it was possible to achieve 30-50 microL blood. Furthermore, a small amount of extra blood was sampled before and after the four samplings for testing of whether the sampling induced a blood glucose change over the 90 min test period. All methods resulted in acceptable amounts of plasma. Clots were observed in a sparse number of samples with no significant differences between the methods. Periorbital puncture did not lead to any haemolysed samples at all, and lateral tail incision resulted in only a few haemolysed samples, while puncture or amputation of the tail tip induced haemolysis in a significant number of samples. All methods, except for puncture of the tail tip, influenced blood glucose. Periorbital puncture resulted in a dramatic increase in blood glucose of up to 3.5 mmol/L indicating that it is stressful. Although lateral tail incision also had some impact on blood glucose, it seems to be the method of choice for OGTT, as it is likely to produce a clot-free non-haemolysed sample, while periorbital sampling, although producing a high quality of sample, induces such a dramatic change in blood glucose that it should not be applied for OGTT in mice.