Serum calcitonin forms and concentrations in young and elderly healthy females

Abstract

To further investigate the role of calcitonin (CT) in normal physiology we studied circulating forms and the secretion after “calcium clamp” in young and elderly healthy females. Heterogeneity of CT in serum was disclosed after immunoextraction, fast protein liquid chromatography, and radioimmunoassay in young (27±3 years; mean±SD, n=6) and elderly females (69±6 years, n=11). Three distinct molecular forms appeared with approximate mol wt of 30, 10, and 3–4 kDa. All young women studied had considerable amounts of circulating monomer-like CT whereas several elderly had undetectable or low levels. The influence of age on basal and calcium stimulated, immunoextracted CT in serum was also studied in young (26±4 years; mean±SD, n=13) and elderly (63±6 years; n=12) healthy females. The calcium stimulation was carried out by means of the standardized calcium clamp method, where calcium was kept on a presettled level at 1.45 mmol/liter (±2%) for 60 minutes. CT was immunoextracted from serum in all series of experiments with a polyclonal antiserum directed against the mid-and carboxyterminal region of the CT molecule, and the amount of extracted CT was determined by radioimmunoassay using another polyclonal antiserum against the carboxyterminal portion. After calcium infusion, the increase in CT was significantly higher in young women than in elderly (P<0.05). At basal conditions, the CT levels were not significantly different but slightly higher in young than in elderly females. In conclusion, several elderly women lack monomer-like calcitonin in serum in contrast to young women. After calcium stimulation of calcitonin, young women had higher serum concentrations than elderly women.