Mechanisms for development of diabetic hypertriglyceridemia in streptozotocin-treated rats. Effect of diet and duration of insulin deficiency.

A combined ultrastructural and functional approach was employed to define the effects of duration of diabetes and of diet on various aspects of lipid metabolism in rats with severe streptozotocin (SZ)-induced insulin deficiency. Plasma triglyceride (TG) levels rose to a mean of 479 mg/100 ml 24 h after SZ administration in rats eating a fat-free, high carbohydrate diet as compared to a mean of 324 mg/100 ml in rats eating a high fat diet. These changes were associated with a commensurate increase in hepatocyte Golgi very low density lipoprotein (VLDL) content, but only a small increase in estimates of VLDL-TG secretion rate (post-Triton WR 1339 increment in plasma TG level). Although these findings are consistent with the thesis that VLDL-TG synthesis and secretion are increased 24 h after administration of SZ, it seemed unlikely that the observed increase in VLDL-TG secretion could entirely account for the severity of the hypertriglyceridemia. Thus, although lipoprotein removal rate was not measured directly, it was necessary to postulate that a defect in VLDL-TG removal was also present at this stage. Hypertriglyceridemia was still present 7 days later, only in this instance plasma TG levels were higher in rats eating the high fat diet (a mean of 589 mg/100 ml, as compared to 263 mg/100 ml). Rats with diabetes of 7-day duration had a 50% decrease in both TG entry rate and hepatocyte Golgi complex VLDL content, irrespective of diet. Thus, there was no evidence of increased VLDL-TG secretion in chronic insulin deficiency. In this instance, although not assessed directly, it was necessary to postulate that the hypertriglyceridemia in chronically insulin-deficient rats is due entirely to a defect in lipoprotein removal, involving both dietary and endogenous fat.