The immunoreactive inhibin secretion pattern in the midluteal phase: Relationships with luteinizing hormone and progesterone

With the development of a sensitive radioimmunoassay for inhibin, luteal phase inhibin levels have been noted to parallel progesterone levels and be acutely dependent upon luteinzing hormone (LH) stimulation. To define the midluteal secretory pattern of immunoreactive inhibin and its relationships with LH and progesterone, blood samples were obtained from five normal women every 20 min for a period of 24 h. Individual data series of LH, progesterone and inhibin were analysed for pulsatile using an adaptive-threshold method. Inhibin levels exhibited a relatively frequent, low-amplitude pulsatile secretory pattern (14.6 ± 6.9) pulses/24 h (mean ± SE), amplitude = 17% of the mean inhibin level). In contrast, LH levels demonstrated an infrequent high amplitude secretory pattern (6.2 ± 0.7 pulses/24 h, amplitude = 139% of the mean level). The average progesterone pulse frequency and amplitude were intermediate to LH and inhibin (9.2 ± 1.2 pulses/24 h, amplitude = 36% of the mean progesterone level). In addition, each individual's hormone data were analysed for coincident pulsatile secretion and cross-correlations were performed on the data, with one hormone pattern shifted relative to another by 20-min time intervals. None of the individual inhibin data series showed significant pulse coincidence when compared to the LH or progesterone data series. The cross-correlation analysis, however, revealed a significant (P <0.05) relationship in general trends between the inhibin and LH data series, and the inhibin and progesterone data series in three subjects. These findings suggest that (1) inhibin exhibits a relatively frequent low-amplitude pulsatile secretory pattern in comparison to LH and progesterone in the midluteal phase of the menstrual cycle, and (2) while the secretion of these three hormones in interrelated, there is not a strong coupling between secretory pulses of inhibin and either LH or progesterone pulses.