Stimulatory effect of immunoglobulins and Fc fragments on glucose oxidation and glucose transport by adipocytes

Following our demonstration that human IgG, its Fc fragments and IgM stimulate lipogenesis in adipocytes, we embarked on a study to investigate whether these proteins stimulate the oxidation and transport of glucose by adipocytes, and whether such a stimulation is mediated through the insulin receptor. Using a simplified method for the measurement of [¹⁴C]-carbon dioxide produced from [U-¹⁴C]-glucose by rat adipocytes, we demonstrated that both IgG, Fc fragments and IgM produced a dose-dependent stimulation of oxidation of glucose by adipocytes. These proteins also produced a stimulation of 3-O-methyl-glucose uptake by adipocytes. IgG, Fc fragments and IgM did not, however, alter specific binding of insulin to adipocytes. These data provide further evidence that human IgG and IgM may have a role in regulating metabolic activity of adipose tissue. These effects are exerted independently of the insulin receptor and are probably mediated through the interaction of its Fc fraction with putative Fc receptors on the adipocyte membrane. A similar interaction may be important in the regulation of metabolic activity of other cells with Fc receptors.