EFFECT OF LONG-TERM EXOGENOUS HYPERINSULINEMIA AND FRUCTOSE OR GLUCOSE SUPPLEMENTATION ON TRIGLYCERIDE TURNOVER IN RATS

We examined the effect of long-term (6 months) hyperinsulinemia on VLD L-triglyceride turnover in male Wistar rats. Hyperinsulinemia was indu ced in rats by daily s.c. injection of Ultralente insulin (6 U/day at 19:00). Fructose (F) or glucose (G) was supplied in the drinking water (10%) in order to prevent hypoglycemia. The rats were divided into 5 groups: (1) hyperinsulinemia with F water: group F+I; (2) hyperinsulin emia with G water: group G+I; (3) F water alone: group F; (4) G water alone: group G; and (5) control rats without sugar water group C. Afte r 6 months of daily insulin injection triglyceride secretion rate (TGS R) was estimated using Triton WR1339 in all the rats. Groups F+I and G +I were obese and hypoglycemic compared to the other groups. Fasting p lasma glucose level of group F was higher than any other group value. TGSR of group F+I was significantly higher than that of the control gr oup, while that of group G+I was not, indicating that long-term hyperi nsulinemia can stimulate hepatic triglyceride production when the rats were supplemented only with fructose. On the other hand, the rats in group G+I showed the lowest plasma free fatty acid level of all and th eir postheparin lipolytic activity was significantly elevated compared to that of the control rats. Moreover, they had suppressed plasma tri glyceride levels and its fractional catabolic rate was significantly i ncreased, suggesting that hyperinsulinemia can still stimulate triglyc eride removal from the circulation of glucose supplemented rats even a t month 6. In conclusion, exogenous hyperinsulinemia can stimulate hep atic triglyceride secretion even after 6 months duration when suppleme nted with fructose, while its stimulating effect on triglyceride remov al from the circulation can be seen only with glucose supplementation. Thus, the effect of long-term hyperinsulinemia on plasma triglyceride turnover differs depending on the supplemented monosaccharides. (C) 1 997 Elsevier Science Ireland Ltd.