The luteinizing hormone pulsatile secretion: diurnal excursions in normally cycling and postmenopausal women

Abstract

While numerous investigations have determined characteristics of episodic luteinizing hormone (LH) secretion in women, any diurnal LH rhythmicities during eugonadal and hypogonadal states have not been accurately addressed. Accordingly, blood was sampled at 15-min intervals for 24 h in 45 normally cycling women (16 early follicular (EFP), 14 late follicular (LFP), 15 mid-luteal phase (MLP) women) and in eight postmenopausal women (PMW). Pulse attributes (amplitudes, interpulse intervals) determined in the LH secretory profiles were fitted to cosinor functions to assess diurnal variabilities. In both eugonadal women and PMW, significant (p less than 0.05 or less) diurnal excursions were observed in mean LH levels, with maximal acrophase amplitudes occurring in the EFP and MLP. While these 24-h swings peaked at comparable times (11.00-17.00) during the menstrual cycles, a significant (p less than 0.001) shift in acrophase times to early morning hours (05.30) was noted for PMW. Significant (p less than 0.05 or less) 24-h periodicities were also found for the LH pulse amplitudes. LH pulses were of greater magnitudes during night hours in both cycling women and PMW. A slowing of LH pulses (p less than 0.05 or less) was noted during sleep in EFP and, distinctly, in MLP women. These observations demonstrate diurnal variations in LH secretion and its pulsatile attributes in eugonadal women. Differences in time course and magnitude of these diurnal excursions may be explained by variations in the sex steroid environments. In turn, steroids may modulate other neuroendocrine determinants regulating central time-keepers.