Serum leptin in subjects with impaired glucose tolerance in relation to insulin sensitivity and first-phase insulin response.

Objective: It has been suggested that insulin could regulate the secretion of leptin, the ob gene product, but the findings have been contradictory. Therefore, we studied the association between leptin and insulin secretion and insulin sensitivity in impaired glucose tolerance (IGT).

Subjects: 39 obese subjects (17 men, 22 women, body mass index (BMI) 30.6 +/- 0.6 kg/m2, age 54 +/- 1 y, mean +/- s.e.m.) with IGT.

Measurements: Leptin, insulin sensitivity and first-phase insulin response (frequently sampled intravenous glucose tolerance test), anthropometry, infrared densitometric assay.

Results: Leptin correlated with BMI (r = 0.36, P = 0.022), fat percent (r = 0.74, P < 0.001) and fat mass (r = 0.53, P < 0.001). After adjustment for sex and fat mass, leptin showed no significant linear correlation with fasting insulin, insulin sensitivity or first-phase insulin response.

Conclusion: In obese IGT subjects fat mass is the main correlate of serum leptin concentration. First-phase insulin response or the degree of insulin resistance are not associated with leptin in IGT.