Effects of oral contraceptive and estrogen administration on plasma calcitonin in pre- and postmenopausal women

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Abstract
Estrogen (E) therapy and administration of oral contraceptives (OC) reportedly increase plasma calcitonin (CT) concentrations in women, effects said to mediate in part the beneficial actions of E on bone. To further examine this theory, we tested the effects of three cycles of OC therapy in 12 young women, comparing them to 10 healthy women before and after three normal menstrual cycles. We also determined the effects of 3 months of E therapy (ethinyl estradiol, 20 μg/day, 25 of 30 days) in 14 healthy postmenopausal women, using a crossover design (studied after 3 months with and 3 months without E). We determined CT by radioimmunoassay (antiserum G-1701) in whole plasma (iCT) and silica cartridge extracts of plasma (exCT) after overnight fasting, after calcium (Ca) infusion (2 mg Ca/kg over 5 minutes), and during a normal day at 0800, 1200, 1700, and 2000 h. In no control study was there a significant diurnal change in iCT or exCT, and neither OC nor E therapy altered this. Similarly, OC administration did not affect basal CT levels or the normal iCT and exCT responses to Ca infusion. E therapy induced expected changes in serum Ca, phosphorus, and alkaline phosphatase and urinary Ca and cAMP excretion; basal and diurnal plasma exCT levels were decreased significantly, consonant with the decrement in serum Ca. E did not alter normal iCT and exCT responses to Ca infusion. Thus, administration of either OC or E has no stimulatory effect on CT secretion, which suggests that the beneficial actions of E on bone are not mediated through CT-induced inhibition of bone resorption. Interaction of E with CT action at the cellular level is not excluded by these findings, but there are no data to support such a proposal.
Funding Information
  • National Institutes of Health ((RR-585, AR-32526))