Pulse amplitude and frequency modulation of parathyroid hormone in early postmenopausal women before and on hormone replacement therapy.

Abstract

Although the pathophysiology of postmenopausal osteoporosis has been investigated extensively, it is still not established in what respect PTH is related to the events. Recently, consistent data on the pulsatile secretion of PTH in man have been published. In this study intact PTH was measured in six early postmenopausal women before and after 6 months of hormone replacement therapy (HRT; 0.6 mg conjugated estrogens and 5 mg medrogestone). In addition to parameters of calcium metabolism and bone mass and to control HRT, intact PTH was measured in blood drawn over 6 h every 2 min. With HRT there was a 30% reduction in PTH secretion. Both the amount secreted per pulse (baseline, 26.8 +/- 6.9 ng/L; HRT, 21.4 +/- 7.6 ng/L; P < 0.05) as well as the basal secretion (baseline, 232.6 +/- 117.6 ng/L.h; HRT, 145.5 +/- 80.0 ng/L.h; P < 0.01) were reduced, whereas the pulse count per h remained constant (baseline, 5.1 +/- 2.2; HRT, 5.1 +/- 1.3). Power spectrum analysis showed a shift in spectral maxima consistent with these findings. Ionized and total calcium were slightly, but nonsignificantly, reduced with treatment. In summary we conclude that in early postmenopausal women, HRT reduces the secretion of PTH by reducing both the basal secretion and the amount secreted per pulse. It is conceivable that some of the known effects of HRT on bone metabolism might be mediated by the modulation of PTH secretion.