ESTIMATION OF INSTANTANEOUS SECRETORY RATE OF LUTEINIZING HORMONE IN WOMEN DURING THE MENSTRUAL CYCLE AND IN MEN

In both men and women the pulsatile secretory pattern of LH has been extensively characterized. In the present study we used the algorithm for computation of instantaneous secretory rate (ISR) incorporated into the DETECT program to evaluate the secretory activity of gonadotrophs in vivo. We studied the pulsatile release of LH in four healthy women during four phases of the same menstrual cycle (early and late follicular and luteal phases) and in five healthy men. Computation of ISR permitted us to estimate the frequency and the duration of the secretory events from the gonadotrophs. Samples were collected every 10 min for 6 h. The apparent LH pulsatile frequency during the menstrual cycle varied from 5.0±0.8 (mean±SD) during the early follicular phase (EFP) to 5.3±1.2 peaks/6h during the late follicular phase (LFP), to 3.3±1.0 during early luteal phase (ELP) and to 5.3±0.4 peaks/6h during the late luteal phase (LLP). The mean pulse duration also changed throughout the phases of the cycle (EFP 47.4±13‐2 min; LFP 55‐4±21.6 min; ELP 100±50.4 min; LLP 48.1±11 min). In healthy men the LH pulse frequency was 3.8±1.6 peaks/6h and the duration was 71‐5±35.7 min. When time series were analysed for ISR determination no significant changes were observed between the LH pulse frequency detected on ISR and that observed on plasma concentrations. Conversely, a significant reduction of the duration of the pulses was found when using ISR instead of plasma concentration. The mean pulse duration in ISR does not show any significant difference between men (22±10.3 min) and women in the four different phases of the cycle investigated (EFP = 25.2±12 min; LFP = 28±12 min; ELP = 21.6±11 min; LLP = 20±13 min). In conclusion these data suggest that the duration of the LH secretion by the gonadotrophs is not different in men and in women and implied that LH mass and the rate, but not the duration, of the secretory bursts are regulated by GnRH and that steroids affect LH pulsatile secretion by influencing the frequency and/or amplitude of the pulses.