Insulin-mediated increases in the HDL cholesterol/cholesterol ratio in humans.

The role of insulin in the regulation of lipoprotein cholesterol distribution was studied in 18 human volunteers who were of normal weight, normolipemic, and glucose-tolerant. We used the euglycemic clamp technique and made comparisons with six saline-infused controls. While total cholesterol and low density lipoprotein cholesterol levels fell similarly by 6 hours in both groups (p = NS), there was a greater decrease in triglyceride levels (p less than 0.02) but less decrease in high density lipoprotein cholesterol levels (p less than 0.02) in the insulin-infused group. These changes resulted in both a higher high density lipoprotein cholesterol/total cholesterol ratio (p = 0.01) and a higher high density lipoprotein cholesterol/low density cholesterol ratio (p = 0.02) in the insulin-infused group. The timing of this effect of insulin implies a mechanism unrelated to high density lipoprotein turnover. Thus, insulin infusion during euglycemia appears to alter cholesterol distribution favorably in normal subjects.