Calcium-Regulating Hormones across the Menstrual Cycle*

Midcycle elevations of serum PTH, calcitonin (CT), and 1,25-dihydroxyvitamin D [1,25-(OH)2D] in women have been reported. To examine the effects of cyclic changes in ovarian steroid secretion on calcitropic hormone concentrations, we used a cytoreceptor assay for 1,25-(OH)2D and homologous RIAs for PTH and CT to measure these hormones in daily blood samples obtained from six women throughout the menstrual cycle. Significant changes in serum PTH, CT, 1,25-(OH)2D, calcium, and phosphorus concentrations during the cycle were not found; transverse means (+/- SE) were 101 +/- 3.5 pg/ml for PTH, 30.8 +/- 1.8 pg/ml for CT, and 40.1 +/- 1.7 pg/ml for 1,25-(OH)2D. In addition, CT reserve was assessed by calcium infusion (3 mg/kg, iv, in 10 min) during the early and late follicular and midluteal phases of the cycle. Although serum CT increased significantly (P less than 0.01) after calcium infusion, the mean (+/- SE) increment (23.2 +/- 2.2 pg/ml) did not significantly differ in the three phases of the cycle (early follicular, 23.8 +/- 4.0; late follicular, 23.3 +/- 3.4; midluteal, 22.5 +/- 4.1). Our data do not support previous reports of midcycle elevations in serum PTH, CT, and 1,25-(OH)2D concentrations, and we conclude that serum concentrations of the calcitropic hormones do not significantly vary during the menstrual cycle.