Study 2. An index of the whole body rate of glucose disposal (R d′) was calculated from the plasma disappearance of 3H-2DG according to [19]. R g′ was calculated from plasma kinetics of 3H-2DG and tissue retention of phosphorylated 3H-2DG based on the methods described in [18]. Note that R g′ data for the liver is not presented due to poor metabolic trapping of 2DG in this tissue [25]. Tissue level insulin action was assessed quantitatively in a particular group by fitting R g′ versus plasma insulin level ([Ins]) results for individual animals to a dose-response curve; that is, (1)Rg′=Rg′(min)+(Rg′(max)−Rg′(min))(1+10(logEC50−log[Ins])b), where R g′(min) is the asymptotic value of R g′ estimated as [Ins]→0, R g′(max) is the asymptotic value of R g′ as [Ins]→∞, EC50 is the [Ins] required to affect a half maximal response; that is, (R g′(min) + R g′(max))/2, b is a slope factor). Note that EC50 is the strict quantitative definition of insulin sensitivity, and the difference, R g′(max)–R g′(min), is the insulin responsiveness.
