Specific physiological regulation of luteinizing hormone secretory events throughout the human menstrual cycle: new insights into the pulsatile mode of gonadotropin release

Abstract

Abstract To investigate the physiological regulation of luteinizing hormone (LH) secretory events and the endogenous clearance of this hormone, we applied multiple-parameter deconvolution analysis to serum LH concentration-time series obtained from normal women during three phases of the menstrual cycle. The number of significant LH secretory bursts (/24 h) was maximal in the late follicular (LF) phase (27 +/- 1.6; mean +/- SEM), minimal in the mid-luteal (ML) phase (10 +/-1.0) and intermediate in the early follicular (EF) phase (18 +/- 1.4). Similarly, the half-duration of the secretory impulse (min) was different at each phase of the cycle with values of 6.5+/-1.0, 3.5+/-0.9 and 11 +/- 1.1 during the EF, LF and ML phases, respectively. In contrast, there were no cycle-dependent differences in the LH half-life or in the total daily secretion of LH. When maximal secretory impulse amplitudes were examined, a putative bimodal distribution was found in the ML but not the EF or LF phases. The amplitudes for the large ML impulses, the LF and EF impulses and the small ML impulses were 0.95 +/- 0.05, 070 +/- 0.03, 0.43 +/- 0.02 and 0.26 +/- 0.02, respectively. The mass (mlU/ml) of hormone secreted within bursts was minimal in the LF phase (2.1 +/- 0.1), maximal in the large ML impulses (10.2 +/- 0.5) and intermediate in the EF (2.8 +/- 0.1) and small ML (3.1 +/-0.3) secretory impulses. There was no evidence of tonic (i.e. inter-secretory burst) LH secretion during any phase of the menstrual cycle. The early morning hours of the EF phase were characterized by fewer secretory bursts of greater amplitude. During the ML phase, autocorrelation analysis of inter-secretory burst intervals revealed a negative association indicating that high frequency events both precede and follow secretory pauses. In addition, secretory burst amplitude and both the preceding and following inter-secretory burst interval was correlated to secretory burst amplitude. These new data on the nature of regulated LH secretion indicate that specific facets of spontaneous LH secretory events are controlled throughout the menstrual cycle. Such observations offer a basis for defining altered secretory dynamics in a variety of pathophysiologic situations.