Dependence of Mean Levels of Circulating Luteinizing Hormone upon Pulsatile Amplitude and Frequency*

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Abstract
We investigated the relationship between mean serum LH levels and the amplitude and frequency of LH pulses in 23 women. Serum LH levels were determined every 10 min for 8-12 h in 6 normal cycling women during the follicular phase of the menstrual cycle, in 9 women with polycystic ovary syndrome, and in 8 postmenopausal women. A striking linear correlation (r = 0.98; P < 0.00001) was found between the mean LH value during the study period (range, 11.1-137.7 IU/L) and the product of the mean LH pulse amplitude and frequency. The interdependence of these variables was further explored using a mathematical model which identfies two main determinants of the slope of the regression line relating the mean LH value to the product of mean pulse amplitude and frequency: 1) the set of constants that specify the biexponential disappearance pattern of LH from serum and 2) the fraction of LH associated with a given pulse which is released from the anterior pituitary after the peak peripheral LH level is reached. Our data, viewed in the light of this model, suggest that 1) the rate at which LH is cleared from the peripheral circulation (expressed as percentage removed per unit time) is independent of both LH concentrations and the sex steroid milieu, and 2) most circulating LH is released in discrete pulses and little, if any, is released in a nonpulsatile or "tonic" mode.

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