Comparison of the effects of insulin and H2O2 on adipocyte glucose transport

The abilities of insulin and the insulin mimickers spermine and H₂O₂ to stimulate 3-O-methyl glucose transport in isolated rat ft cells were stuided in an attempt to determine possible common mechanisms of action. All three agents caused a seven- to 12-fold stimulation of initial rates of glucose transport with insulin being the most effective agent. Insulin and spermine displayed similar time courses for the onset of their stimulation of transport; an initial lag before any effect was seen and then a gradual rise until the full effect was reached. The time course of H₂O₂ activation of glucose transport was different since stimulation was seen at the earliest time point tested and then gradually rose to the maximal effect. Trypsinization of cells removed insulin receptors and rendered the cells insensitive to insulin but not to spermine or H₂O₂. However, trypsinization did alter the time course of H₂O₂ action, causing an initial lag phase to appear and a general slowing of the activation kinetics. Pretreatment of cells with 2,4-dinitrophenol to lower ATP levels prevented the stimulatory effects of insulin and the mimickers. All three of the agents revealed a similar temperature dependency for stimulated glucose transport, resulting in linear Arrhenius plots with activation energies of 10.2–11.4 kcal/mole. These results show that (1) H₂O₂ does not act directly on the glucose transport system of rat adipocytes and (2) insulin and H₂O most likely act through a common energy-dependent biochemical pathway to stimulate glucose transport, but H₂O₂ enters the stimulus-response sequence distal to the initial steps in insulin action.