The purpose of the experiments described in this paper was to determine whether phenformin altered the metabolism of glucose in subjects in whom it did not lower the blood sugar. Glucose-1-C-14 was utilized to investigate the metabolism of glucose in eight normal and eight obese subjects before and after phenformin.

Phenformin increased the turnover, recycling and conversion of glucose to lactate and decreased the oxidation of glucose in all of the normal subjects studied. The increase in glucose turnover was due entirely to the increase in glucose recycling since net glucose turnover (glucose derived from all sources except the Cori cycle) did not change. Phenformin also increased glucose turnover and recycling in obese subjects but in contrast to normals, its effect.s on glucose oxidation and glucose conversion to lactate were more variable.

These results establish that phenformin has clearly defined effects on the metabolism of glucose in subjects in whom it exerts no hypoglycemic action and support the concept that phenformin increases glucose utilization by diverting it from oxidative to nonoxidative pathways in peripheral tissues.

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