Regulation of calcium-regulating hormones by exogenous sex steroids in early postmenopause.

A major function of calcitonin in humans appears to be maintenance of the skeleton. There is a marked sex difference in circulating calcitonin levels: women have much lower levels. This has led to speculation that calcitonin lack may be one factor involved in the pathogenesis of postmenopausal bone loss. We have measured levels of calcitonin and the other major calcium-regulating hormones in healthy women during the early menopause, and studied the effects of reversing their oestrogen deficiency with natural and synthetic oestrogen. The major findings were that calcitonin levels were increased by oestrogen administration (P less than 0.02-less than 0.001) and that the levels of the bone-resorbing hormones, parathyroid hormone and 1,25 dihydroxyvitamin D, were not higher in postmenopausal than in premenopausal women. We suggest that loss of oestrogen at the menopause accelerates the natural age-related decline of calcitonin secretion, thus further decreasing the calcitonin levels. This leads to increased sensitivity of the skeleton to the actions of the bone-resorbing hormones. It seems likely that the well-known effect of oestrogen in preventing postmenopausal bone loss is achieved, at least in part, by enhancement of calcitonin secretion.