Journal of Clinical Endocrinology & Metabolism, Vol 74, 413-418, Copyright © 1992 by Endocrine Society

ARTICLES

Effects of conjugated estrogen on the calcitriol response to parathyroid hormone in postmenopausal women

R Marcus, ML Villa, M Cheema, C Cheema, K Newhall and L Holloway
Department of Medicine, Stanford University, California 94305.

We evaluated the effects of estrogen on the calcitriol response to the active peptide, human PTH(1-34), in postmenopausal women. Fifteen women were studied before and again after at least 1 month of treatment with conjugated equine estrogens, 1.25 mg/day. Six women received two series of four graded peptide infusions, each with the sequence 200, 400, 800, and 1600 USP U hPTH(1-34). Nine women received only one dose of peptide, either 200 or 800 U, before and while taking estrogen. Baseline values and the incremental and percent changes in circulating calcitriol 24 h after the 20-min infusions were evaluated. Estrogen treatment resulted in significant reductions in blood levels of calcium (2.26 +/- 0.03 mmol/L vs. 2.16 +/- 0.02, P less than 0.05) and phosphorus (1.23 +/- .05 mmol/L vs. 1.14 +/- 0.03, P less than 0.005), a rise in serum calcitriol concentrations (42.2 +/- 3.9 pg/mL vs. 28.6 +/- 3.1, P less than 0.005), and no change in circulating PTH. The rise in calcitriol after 200 U hPTH(1-34) was significantly greater on estrogen (17.6 +/- 2.0 pg/mL vs. 9.5 +/- 1.8, P less than 0.01), but estrogen did not alter incremental responses to larger doses. When results were normalized for differences in baseline values, the estrogen-related change in response to 200 U was no longer significant. hPTH(1-34) acutely increased urinary clearance of cAMP and phosphorus, but estrogen did not affect this response. We conclude that exogenous estrogen does not increase renal sensitivity to PTH in postmenopausal women.

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