ULTRADIAN OSCILLATIONS OF LEPTIN SECRETION IN HUMANS

We have recently demonstrated the nocturnal increase in leptin secreti on in humans. In the present study we have examined the pulsatile patt ern of leptin secretion using two different experimental protocols. Th e first protocol utilized blood samples withdrawn at 30 minute interva ls immediately after meals, at 1 hour intervals between meals, and at 2 hour intervals during the night from 4 lean, 11 obese, and 5 obese N IDDM subjects. Analysis of circulating leptin levels by ULTRA algorith mic program and using matched intra-assay coefficient of variations de monstrated 1 to 7 ultradian oscillations with a mean of 3.25 +/- 0.36 (SEM) pulses per 24 hour period (period: 10.0 +/- 1.5 hours; mean rela tive amplitude: 0.52 +/- 0.06, n=20). Significant positive correlation s were observed for changes in absolute amplitude with body mass index (p<0.025) and fasting leptin levels (p<0.0001). In the second series of experiments utilizing 15 minute blood sampling from 10 overnight fa sted obese subjects (BMI 35.9 +/- 2.0 kg/m(2)), ultradian oscillations for leptin were more frequent, i.e., 2 to 7 oscillations (4.20 +/- 0. 59), over a 12 hour duration (period: 3.44 +/- 0.49; mean relative amp litude: 0.28 +/- 0.03). The number of oscillations over a 12 hour peri od correlated significantly with BMI (p<0.001), fasting leptin levels (p<0.01), and absolute amplitude (p<0.005) in a 15 minute sampling pro tocol. In summary, similar to other hormones, ultradian oscillations o f leptin are observed in humans, although the physiological significan ce in relation to obesity or feeding behavior is not yet understood. ( C) 1996 Academic Press, Inc.