A new rat model of type 2 diabetes: the fat-fed, streptozotocin-treated rat.

This study was initiated to develop an animal model of type 2 diabetes in a non-obese, outbred rat strain that replicates the natural history and metabolic characteristics of the human syndrome and is suitable for pharmaceutical research. Male Sprague-Dawley rats (n = 31), 7 weeks old, were fed normal chow (12% of calories as fat), or high-fat diet (40% of calories as fat) for 2 weeks and then injected with streptozotocin (STZ, 50 mg/kg intravenously). Before STZ injection, fat-fed rats had similar glucose concentrations to chow-fed rats, but significantly higher insulin, free fatty acid (FFA), and triglyceride (TG) concentrations (P < .01 to .0001). Plasma insulin concentrations in response to oral glucose (2 g/kg) were increased 2-fold by fat feeding (P < .01), and adipocyte glucose clearance under maximal insulin stimulation was significantly reduced (P < .001), suggesting that fat feeding induced insulin resistance. STZ injection increased glucose (P < .05), insulin (P < .05), FFA (P < .05), and TG (P < .0001) concentrations in fat-fed rats (Fat-fed/STZ rats) compared with chow-fed, STZ-injected rats (Chow-fed/STZ rats). Fat-fed/STZ rats were not insulin deficient compared with normal chow-fed rats, but had hyperglycemia and a somewhat higher insulin response to an oral glucose challenge (both P < .05). In addition, insulin-stimulated adipocyte glucose clearance was reduced in Fat-fed/STZ rats compared with both chow-fed and Chow-fed/STZ rats (P < .001). Finally, Fat-fed/STZ rats were sensitive to the glucose lowering effects of metformin and troglitazone. In conclusion, Fat-fed/STZ rats provide a novel animal model for type 2 diabetes, simulates the human syndrome, and is suitable for the testing of antidiabetic compounds.

Effect of masoprocol on carbohydrate and lipid metabolism in a rat model of Type II diabetes.

Extracts of the creosote bush (Larrea tridentata, family Zygophyllaceae) have long been used as a folk remedy for Type II (non-insulin-dependent) diabetes by native Americans in southwestern North America. In this study we have evaluated the metabolic effects of masoprocol, a pure compound isolated from the creosote bush, in a rat model of Type II diabetes. Animals were fed a 20% fat (by weight) diet for 2 weeks prior to intravenous injection with streptozotocin (STZ, 0.19 mmol/kg). Diabetic animals (glucose 16-33 mmol/l) were treated with vehicle, metformin (0.83 mmol/kg body weight) or masoprocol (0.83 mmol/kg body weight) twice a day for 4 days. Masoprocol treatment lowered glucose concentrations an average of 35% compared with vehicle (14.2+/-1.1 vs 21.7+/-1.0 mmol/l, p < 0.001), a reduction similar to metformin treatment (12.8+/-0.9 mmol/l), without any change in insulin concentration. Masoprocol treatment also lowered triglyceride concentrations 80% compared with vehicle (1.0+/-0.1 vs 4.8+/-0.3 mmol/l, p < 0.001), a reduction far greater than following metformin treatment (3.6+/-0.3 mmol/l). Non-esterified fatty acid and glycerol concentration were decreased by approximately 65% by masoprocol compared with vehicle, a reduction approximately twice as great as seen with metformin (p < 0.001). The effect of masoprocol on in vivo insulin-mediated glucose disposal was evaluated by infusing fat-fed/STZ rats with glucose (0.22 mmol kg x min(-1)) and insulin (30 pmol x kg x min(-1)) for 5 h. In response to the infusion, steady-state plasma glucose concentrations were reduced 30% in masoprocol-treated animals compared with vehicle controls (p < 0.05) with no change noted in rats treated with metformin. The effect of masoprocol treatment was also tested in primary adipocytes isolated from normal animals. Adipocytes treated with masoprocol (30 micromol/l) had higher basal and insulin-stimulated glucose clearance than did adipocytes treated with vehicle (p <0.05). These data show that masoprocol decreases both plasma glucose and triglyceride concentrations in fat-fed/STZ rats, presumably as a result of its ability to both increase glucose disposal and decrease lipolysis.