Does estrogen replacement therapy influence parathyroid hormone responsiveness to exogenous hypercalcemia in postmenopausal women?

In postmenopausal women PTH suppression by exogenous calcium is reduced. To test whether this finding might be caused by estrogen deficiency 9 postmenopausal women were given transdermal estradiol (E2) treatment for 3 months at a dose of 100 micrograms/day. PTH reactivity to iv administration of CaCl2 was determined before and at the end of the E2-treatment period. Compliance to treatment was checked by determination of serum levels of E2 and FSH. The E2 level rose from 0.1 +/- 0.02 (mean +/- SE) to 0.46 +/- 0.10 mmol/l p < 0.01), whereas the corresponding FSH level declined from 77.5 +/- 7.4 to 33.9 +/- 5.7 U/l p < 0.01). This suggests good compliance. At the end of E2-treatment period calcium administration induced a higher PTH suppression as compared with control value (the PTH decremental area 2123 +/- 270 vs 1253 +/- 253 ng/l x min, p < 0.05), although a lower calcemic response was attained (the Ca incremental area 32.6 +/- 6.1 vs 47.4 +/- 4.5 mmol/ml x min, p < 0.05). These results imply that parathyroid glands are dependent on an adequate estrogen provision to respond normally to serum calcium changes.