Phenformin stimulation of insulin binding to human cultured lymphocytes

The effects of the oral hypoglycemic agent, phenformin, were studied on the binding of 125I-insulin to its receptors in IM-9 human cultured lymphocytes. Three h after the addition of 5 μg/ml of phenformin to these cells there was detectable stimulation of 125l-insulin binding; maximal effects were seen after 18 h. A detectable effect of phenformin was seen at 1 μg/ml and maximal effects were seen at 5 μg/ml. These studies demonstrate therefore that phenformin increases the binding of 125l-insulin to human cultured lymphocytes, and raise the possibility that phenformin could act in vivo to regulate insulin receptors.