Regulation of calcitonin and parathyroid hormone secretion by oestrogens

Calcitonin is a peptide hormone secreted by C-cells which, in humans, are found mainly in the thyroid gland. It now seems that a major physiological function of this hormone in man is the long-term maintenance of the skeleton achieved by control of bone resorption. A marked sex difference in circulating calcitonin levels normally exists, with a relative deficiency in women as compared to men. It has now been found that oestrogens regulate calcitonin secretion and it appears likely that the loss of ovarian function at the menopause accelerates the natural decline in calcitonin secretion which occurs with age. Thus, post-menopausal women are more markedly calcitonin-deficient. Levels of the bone-resorbing hormones, parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D are not elevated post-menopausally and it seems likely that the increased bone resorption which leads to post-menopausal bone loss is due mainly to the loss of oestrogen and calcitonin secretion.