Figure 5.

Euglycemic clamp experiments in which insulin was infused stepwise either systemically or into the portal vein of the liver. Infusion rates were chosen to attain approximately matched systemic insulin levels (see text; (A)). A plot of systemic insulin levels as a function of insulin infusion (B) yielded a lower slope with portal infusion due to first-pass liver insulin clearance. The ratio of the slopes in Figure 5B yielded a direct and accurate measure of first-pass hepatic clearance of insulin. From Ref. [33].