Cultured human fibroblasts represent an appropriate model for studying both insulin receptor interaction and hormone responsiveness. We have investigated the properties of the pyruvate dehydrogenase multienzyme complex (PDC) and have studied the effects of various concentrations of porcine and biosynthetic human insulin (BHI) on the activity of the enzyme. Under optimal conditions of the assay, both BHI and porcine insulin activated PDC in a dose-dependent fashion in which full activation of the enzyme was achieved with 10−8 M insulin. The half-maximal concentration for porcine and human insulin was similar, occurring at the level of 5 × 10−9 M for activation of the PDC of human fibroblasts.

We conclude that the PDC of cultured human fibroblasts is activated by both human and porcine insulin at a comparable physiologic concentration. Human fibroblasts may therefore serve as a useful model to study insulin action in isolated human tissue.

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