Effects of oral contraceptive and estrogen administration on plasma calcitonin in pre- and postmenopausal women : J. Bone Miner Res.; 4/1 (89–95)/1989/

Abstract

Estrogen (E) therapy and administration of oral contraceptives (OCs) reportedly increase plasma calcitonin (CT) concentrations in women effects said to mediate in part the beneficial actions of E on the bone. To further examine this theory the authors tested the effects of 3 cycles of OC therapy in 12 young women comparing them with 10 healthy women before and after 3 normal menstrual cycles. They also determined the effects of 3 months of E therapy (ethinyl estradiol 20 mcg/day 25 of 30 days) in 14 healthy postmenopausal women using a crossover design (studied after 3 months with and 3 months without E). The authors 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 hours. In no control study was there a significant diurnal change in iCT or exCT and neither OCs 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 OCs 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. (authors)