ENTRAINMENT OF THE DIURNAL RHYTHM OF PLASMA LEPTIN TO MEAL TIMING

To identify the physiologic factor(s) that entrain the diurnal rhythm of plasma leptin, leptin levels were measured hourly after changes in light/dark cycle, sleep/wake cycle, and meal timing, Four young male s ubjects were studied during each of two protocols, those being a simul ated 12-h time zone shift and a 6.5-h meal shift, During the baseline day, plasma leptin demonstrated a strong diurnal rhythm with an amplit ude of 21%, zenith at 2400 h, and nadir between 0900 and 1200 h, Acute sleep deprivation did not alter plasma leptin, but day/night reversal (time zone shift) caused a 12+/-2 h shift (P<0.01) in the timing of t he zenith and nadir, When meals were shifted 6.5 h without changing th e light or sleep cycles, the plasma leptin rhythm was shifted by 5-7 h (P<0.01), The phase change occurred rapidly when compared with change s in the diurnal rhythm of cortisol, suggesting that leptin levels are not acutely entrained to the circadian clock. The leptin rhythm was a ltered by meal timing in a manner very similar to the rhythm of de nov o cholesterol synthesis. We conclude that the diurnal rhythm of plasma leptin in young males is entrained to meal timing.