Pulse amplitude and frequency modulation of parathyroid hormone in primary hyperparathyroidism

Pulsatile secretion of PTH in human subjects has been described recently. However, the pattern of PTH secretion in primary hyperparathyroidism (pHPT) remains to be characterized. In this study intact PTH was measured in 9 female patients with pHPT. As a control group we present data from 10 postmenopausal women. In addition to parameters of calcium metabolism and bone mass, PTH was measured in samples drawn over 4 or 6 h every 2 min by central venous blood sampling. The mean intact PTH concentration was 39.0 +/- 20.3 ng/L in healthy women and 193.2 +/- 127.9 ng/L in female patients with pHPT (P < 0.01). Pulse rhythm analysis showed significant differences between both groups for total PTH secretion per h (patients, 1196.4 +/- 485.3 ng/L; control group, 271.7 +/- 132.2 ng/L), basal PTH secretion per h (patients, 852.4 +/- 459.1 ng/L; control group, 185.6 +/- 126.1 ng/L), and average PTH secretion per pulse (patients, 112.6 +/- 54.8 ng/L; control group, 23.2 +/- 7.1 ng/L). Both patients and control subjects had, on an average, five pulses per h, and the pulsatile secretion accounted for about 50% of the total secretion. Differences in power spectrum analysis were consistent with these findings. The cross-correlation of PTH and calcium indicates an impaired feedback regulation in pHPT. PTH secretion in female patients with pHPT results from both an increased basal secretion and an increased amplitude of PTH pulses. Other features of secretion are the same as those in normal women. Feedback regulation of PTH and calcium is impaired in pHPT.

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

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.