Influence of estrogen replacement therapy on endogenous calcitonin production rates

Calcitonin is now a well-accepted therapy for inhibition of bone loss, both in the first years of menopause and in established osteoporosis. However, its exact role in the pathogenesis of that disease as well as the interactions between calcitonin production and estrogen metabolism remain unsolved. In order to clarify the influence of estrogen replacement therapy (ERT) on calcitonin secretory capacity, we measured whole plasma immunoreactive calcitonin basal levels, metabolic clearance rates and production rates in a group of postmenopausal women, before and after a daily intake for 28 days of 0.625 mg/day of conjugated equine estrogens, and again 4 weeks after the withdrawal of that estrogen replacement therapy. No significant changes appeared in immunoreactive calcitonin or immunoreactive calcitonin metabolic clearance rate but the production rate significantly increased over the 28 days (mean +/- SEM, from 21.3 +/- 5.1 pg/ml to 25.2 +/- 5.9 pg/ml, p less than 0.05), and then decreased 4 weeks after therapy was withdrawn to the initial level (17.9 +/- 3.6 pg/ml). We concluded that estrogen replacement therapy significantly increases calcitonin secretory capacity. This confirms the interactions between calcitonin production and estrogen metabolism, and may provide an explanation concerning the mode of action of estrogen replacement therapy in prevention of postmenopausal bone loss.