NOCTURNAL RISE OF LEPTIN IN LEAN, OBESE, AND NON-INSULIN-DEPENDENT DIABETES-MELLITUS SUBJECTS

We studied 24-h profiles of circulating leptin levels using a sensitiv e and specific RZA in lean controls and obese subjects with or without non-insulin-dependent diabetes mellitus (NIDDM) during normal routine activity. Serum leptin levels were significantly higher in obese (41. 7+/-9.0 ng/ml; n = 11) and obese NIDDM (30.8+/-6.7; n = 9) subjects co mpared with those in lean controls (12.0+4.4, n = 6). In all the three groups, serum leptin levels were highest between midnight and early m orning hours and lowest around noon to midafternoon. The nocturnal ris e in leptin levels was significant when data were analyzed by ANOVA (l ean: F = 3.17, P < 0.0001, n = 4; obese: F = 2.02, P < 0.005, n = 11; and obese NIDDM: F = 4.9, P < 0.0001, n = 5), The average circadian am plitude between acrophase and nadir was 75.6% in lean, 51.7%, in obese and 60.7% in obese NIDDM groups, respectively. No significant correla tions (P > 0.05) were observed between circulating levels of leptin an d either insulin or glucose levels in any of the 20 subjects studied f or 24-h profiles. The nocturnal rise in leptin observed in the present study resembles those reported for prolactin, thyroid-stimulating hor mone, and free fatty acids. We speculate that the nocturnal rise in le ptin could have an effect in suppressing appetite during the night whi le sleeping.