Removal of an insulin inhibitor from the rat heart by perfusion.

1. Insulin-stimulated efflux of galactose from the perfused rat heart increased when the Krebs bicarbonate medium was prepared with gassing with CO(2).2. Analysis of the kinetics of efflux in the light of the carrier theory is used to justify the interpretation of the increased rate of efflux as an increased response to insulin.3. With medium prepared with CO(2) gassing, the photoperiodic reduction in insulin response seen previously was not found; but it was seen when cardiac contractility was reduced or eliminated during the period of galactose loading.4. The relation between the increase in galactose efflux with insulin and the insulin concentration conforms to the Michaelis-Menten equation, for perfusates prepared both with and without CO(2) gassing, indicating in the latter case the presence of a competitive inhibitor of insulin.5. It has been previously shown that preparing the perfusate with CO(2) gassing results in increased contractility of the perfused heart and a much increased rate of interstitial washout. The conditions of the enhanced response to insulin are consistent with the removal of the inhibitor from the heart due to the increased rate of interstitial washout. The possible role of the inhibitor in the control of lipid and carbohydrate metabolism is discussed.