Summary. Streptozotocin-induced insulin deficiency of a moderate degree was produced in exercisetrained and sedentary young rats, and determinations made of subsequent changes in plasma glucose, triglyceride, and insulin concentrations. Exercise-training attenuated the rise in both plasma glucose and triglyceride concentrations associated with insulin deficiency. Plasma insulin levels were, if anything, lower in exercise-trained rats. Thus, the beneficial effects of exercise-training on plasma glucose and triglyceride concentrations could not be due to the preservation of endogenous insulin secretion, and appear to be secondary to enhanced insulin sensitivity.Key words: Streptozotocin, exercise-training, diabetic hypertriglyceridaemia, insulin deficiency, glucose, triglyceride, insulin.Plasma concentrations of glucose and triglyceride (TG) are elevated in rats with even a moderate degree of streptozotocin-induced insulin deficiency [1]. There is reason to believe that all of these metabolic abnormalities might be ameliorated if insulin sensitivity could be enhanced, and recent evidence has demonstrated that exercise-training can lead to increased insulin sensitivity in normal rats [2,3]. Given these observations, it seemed reasonable to see if exercisetraining could prevent the rise in plasma glucose and TG concentrations that develop in rats with streptozotocin-induced insulin deficiency.vidually in exercise wheel cages (Wahman Co., Timonium, Maryland, USA), and allowed to run at their own pace. The cages, as supplied by the manufacturer, consist of a rotating wheel cage with the number of revolutions/day recorded by a cyclometer attached to the wheel axis plus an adjoining feed cage. In order to maximize exposure to the wheel, we replaced the feed cage attachment with a small feeding trough large enough to hold 4-5 days food supply. Thus, the exercising animals remained entirely in the wheel portion of the cage to run at will and feed on laboratory chow ad lib from the attached feeding trough. Preliminary studies indicated that approximately two out of three of the rats placed in the modified exercise wheel cages showed a progressive increase in running activity and average between 2.0-2.5 miles/day after 10 days exposure. Animals unable to attain a level of 2.5 miles/day were excluded from the study.Two kinds of experiments were conducted. In the first series of experiments the rats were divided into two groups at the outset -exercised and sedentary -and maintained in this manner for 21 days. On the morning of day 21, all animals were injected in the tail vein with 40 mg/kg of streptozotocin (SZ). Following this, the rats were returned to their original status for another 10 days: i. e., sedentary rats were placed back in conventional cages and exercise-trained rats placed back in exercise cages. Food was removed at 0800 h on the morning of day 31, rats were decapitated at 1300 h, and blood taken for determination of plasma glucose [4], TG [5], and insulin [6] concentrations. All biochemical determinations we...

The effect of exercise training and a sucrose-rich diet on insulin-stimulated glucose disposal was studied in rats with streptozotocin-induced insulin deficiency. Rats were injected with streptozotocin (40 mg/kg), and 3 days later divided into three groups with equal degrees of hyperglycemia. One group of rats was allowed to run spontaneously on exercise wheels, another group remained sedentary but ate a sucrose-rich diet (66% sucrose), and the third also remained sedentary but consumed conventional rat chow. Three weeks later, we determined the effect of these various programs on postabsorptive plasma glucose and insulin levels, as well as on the ability of exogenous insulin to stimulate disposal of a glucose load during a period in which endogenous insulin was suppressed by epinephrine and propanolol. Basal plasma insulin levels were the same in all three groups, but plasma glucose levels were significantly lower (P less than 0.001) in exercise-trained rats, and significantly higher (P less than 0.05) in sucrose-fed rats, than in chow-fed diabetic rats. The inference that exercise training markedly enhanced insulin action in rats with insulin deficiency was borne out by direct estimation of insulin-stimulated glucose disposal. In contrast, sucrose-fed diabetic rats seemed to be more insulin-resistant than chow-fed diabetic rats. These results provide direct evidence that spontaneous exercise can dramatically attenuate the severity of diabetes in insulin-deficient rats by enhancing insulin action. DIABETES 32:165-168, February 1983.

The ability of exercise and diet to modify the effects of moderate streptozotocin-induced insulin deficiency on triglyceride metabolism has been studied in the rat. Insulin-deficient rats allowed to run spontaneously in exercise wheel cages had significantly lower (P less than 0.001) plasma glucose levels (187 +/- 19 mg/dl) than either sedentary (374 +/- 24 mg/dl) or sucrose-fed (450 +/- 13 mg/dl) diabetic rats, despite the fact that plasma insulin levels were comparable in all these groups. Plasma triglyceride (TG) levels in exercise-trained rats with diabetes (51 +/- 5 mg/dl) were actually lower than in control rats with normal glucose tolerance (90 +/- 14 mg/dl). In contrast, plasma TG levels were higher than control levels in diabetic sedentary rats (128 +/- 11 mg/dl), and severe hypertriglyceridemia developed in sucrose-fed diabetic rats (369 +/- 35 mg/dl). The ability of exercise training to attenuate diabetic hypertriglyceridemia, which was observed in both chow-fed and sucrose-fed rats, was secondary to a decrease in TG secretion, and appeared to be related to lower plasma FFA concentrations. In contrast, the accentuation of diabetic hypertriglyceridemia seen in sucrose-fed rats was related to a defect in TG catabolism. Adipose tissue lipoprotein lipase (LPL) activities were essentially identical in all diabetic rats, suggesting that the observed difference in TG kinetics could not be attributed to concomitant increases or decreases in adipose tissue LPL activity. These results emphasize the powerful impact of exercise and diet on TG metabolism in rats with moderate degrees of insulin deficiency.