Lactate Production and Pyruvate Dehydrogenase Activity in Fat and Skeletal Muscle From Diabetic Rats

Abstract

This study was initiated to explore the possibility that an increase in the supply of gluconeogenic precursors contributes to the overproduction of glucose by the liver in NIDDM patients. To address this issue, a form of experimental NIDDM was produced in rats by injecting a low dose (38 mg/kg) of STZ and comparing lactate and alanine production and PDH activity in skeletal muscle and isolated adipocytes from normal and diabetic rats. Skeletal muscle lactate production was measured by using a hindlimb perfusion technique and was significantly greater (P < 0.01) in the diabetic rats compared with two groups of control rats: one perfused at normal glucose levels and the other perfused at glucose concentrations comparable with those observed in diabetic rats. Alanine production by hindlimb from diabetic rats was 46% greater than hindlimbs from control rats perfused at normal glucose levels (P < 0.01) but was not significantly greater than control rats perfused at diabetic glucose levels. The percentage of glucose converted to lactate by muscle from both control groups was 4–5%, significantly lower than the 18% conversion rate observed in diabetic animals (P < 0.001). An increase in the ratio of lactate produced/glucose transport by isolated adipocytes from diabetic rats also was observed when measured in both the basal state (0.65 ± 0.12 vs. 0.15 ± 0.03, P < 0.01) and in the presence of maximal amounts of insulin (0.15 ± 0.02 vs. 0.04 ± 0.01, P < 0.02). Total PDH activity in fat and muscle was similar in both groups of animals, but PDH present in the active form was significantly reduced in the diabetic compared with the normal rats in fat (39 ± 6 vs. 58 ± 5%, P < 0.05) and in muscle (11 ± 5 vs. 47 ± 10%, P < 0.01). In conclusion, low-dose STZ-induced diabetes in rats is characterized by reduced PDH activity and increased lactate production in skeletal muscle and adipose tissue, changes that, in the presence of insulin deficiency, could contribute to enhanced HGP.