Abstract
Effects of continuous insulin infusion on very low density lipoprotein triglyceride kinetics were compared with those of the previously reported injection model in rats. Insulin infusion was achieved by subcutaneous implantation of an osmotic minipump which delivered insulin at a constant rate (6U porcine insulin/day) for 14 days. In the injection model, NPH insulin was given subcutaneously for 14 days twice daily in incrementally increasing doses from 0.5 to 6 U per day. Insulintreated rats received chow plus 10% sucrose in their drinking water in order to avoid profound hypoglycemia. Two control groups, therefore, were needed: chow only and chow plus the same amount of sucrose. Results in the insulin-injected rats were similar to those previously reported: an increase in the rate of triglyceride secretion, a minimal decrease in serum triglyceride, and a 50% decrease in serum glucose and FFA, suggesting that triglyceride removal from the circulation was stimulated more than triglyceride secretion into the circulation in these rats. Insulin infusion produced the same increase in the secretion rate of triglyceride in the face of a decrease, although less pronounced, in serum FFA, suggesting that the majority of triglyceride fatty acids came from a source other than FFA. The infusion model, however, differed from the injection model in producing an elevation in serum triglyceride. This suggests that triglyceride removal was not stimulated in the infusion model as much as in the injection model. It appeared unlikely that changes in triglyceride kinetics were caused by an increase in counter-regulatory hormones, because there was no hypoglycemia in the infusion model.
