Calcitonin, estrogens and the bone

Estrogen deficiency following natural or surgical menopause, is thought to be the main factor leading to postmenopausal bone loss. Furthermore, after estrogen failure a significant reduction of intestinal calcium absorption and a negativization of calcium balance has been observed. The mechanism of estrogen effect on skeletal tissue is not yet fully elucidated. Recently, specific receptors for estrogens in osteoblastic cells have been described; however their low density does not give a full explanation about their functional role. Therefore estrogens act, at least in part, indirectly through calciotropic hormones. In order to further elucidate this issue, we performed some studies in postmenopausal osteoporotic patients and in fertile oophorectomized women. In the first double blind placebo controlled study, after a 1-year estrogen treatment period we observed an increase in bone mineral content in the hormone-treated patients. Furthermore, in all treated patients an improvement of intestinal calcium absorption was detected, while 1,25-dihydroxy-vitamin D serum levels did not show significant changes. To further analyse the relationship between estrogens (E) and calcitonin (CT) in postmenopausal osteoporosis, we performed a double blind placebo controlled study to evaluate the effects of 1-yr estro-progestative treatment on CT secretory reserve, evaluated by calcium infusion test. Blood levels of CT showed a progressive increase during the study period in the hormone-treated group, with a significant increase in the CT response to calcium stimulation test, suggesting a modulation of CT secretion by E. Recently, we performed two studies in fertile oophorectomized women. In the first, we followed longitudinally 24 fertile women for 1 yr. In these patients we measured, before and after oophorectomy, biochemical indexes of bone metabolism and bone mass. During the observation period a significant increase in bone resorption and a significant drop in intestinal calcium absorption was observed. In the second study, performed on 14 women before and 6 months after oophorectomy, a treatment with conjugated estrogens allowed the correction of the primary intestinal defect responsible for the reduced calcium absorption.(ABSTRACT TRUNCATED AT 400 WORDS)