EFFECTS OF ACUTE HYPERINSULINEMIA ON PLASMA LEPTIN CONCENTRATIONS IN INSULIN-SENSITIVE AND INSULIN-RESISTANT PIMA-INDIANS

Leptin, a recently discovered protein produced in adipocytes, may be i mportant in the regulation of body energy stores. In humans, leptin is present in the circulation in direct proportion to the amount of body fat. In rodents, insulin seems to regulate the production of leptin, but there is only limited evidence that this occurs in humans. We, the refore, measured plasma leptin concentrations in 13 insulin-sensitive and 13 insulin-resistant Pima Indians at baseline, at the end of 100 m in of physiologic hyperinsulinemia (mean plasma insulin = 563 pmol/L) and after a further 100 min of supraphysiologic hyperinsulinemia (mean plasma insulin = 11,910 pmol/L), during a 2-step hyperinsulinemic-eug lycemic glucose clamp. At baseline, plasma leptin concentrations were directly related to percent body fat, determined by hydrodensitometry (r = 0.85, P < 0.0001). After adjusting for percent body fat, there we re no differences in fasting plasma leptin concentrations between insu lin-sensitive and insulin-resistant subjects. Plasma leptin concentrat ions did not change in response to insulin in either the insulin-sensi tive or insulin-resistant subjects. These results suggest that insulin does not acutely regulate plasma leptin concentrations in humans.