Leptin levels and luteinizing hormone pulsatility in normal cycling women and their relationship to daily changes in metabolic rate

Objective: To determine whether leptin and LH secretion in normal women is related to changes in metabolic rate. Setting: Academic medical center. Patient(s) and Design: Ten young women with normal weight and menses were studied during the early follicular phase. Leptin and LH levels were sampled every 15 minutes over a 24-hour period. Metabolic rate was frequently sampled using indirect calorimetry. Luteinizing hormone pulsatility was analyzed using a Cluster Program analysis. Intervention(s): None. Main Outcome Measure(s): Leptin, LH, and metabolic rate levels. Result(s): All subjects demonstrated a diurnal leptin curve. Luteinizing hormone pulses were increased in amplitude and slower after the leptin peak. The average (+/- SE) number of LH pulses per 6 hours slowed from 4.30 +/- 0.42 to 3.00 +/- 0.42 pulses after the leptin peak, whereas pulse amplitude increased from 1.64 +/- 0.26 to 2.51 +/- 0.42 mIU/mL after the leptin peak. The LH interpulse interval increased from 85.1 +/- 3.64 minutes to 108.8 +/- 10.26 minutes after the leptin peak. Metabolic rate began to drop approximately 4-6 hours before leptin levels peaked, going from 1.66 +/- 0.24 to 1.15 +/- 0.04 kcal/min after the leptin peak. Conclusion(s): There is a significant association between the timing of the leptin peak, the nightly slowing of LH pulses, and the fall in metabolic rate, suggesting a metabolic cycle in normal individuals.