Calcitonin‐like immunoreactivity in human milk, longitudinal alterations and divalent cations

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Abstract
The concentration of immunoreactive calcitonin (iCT) in human milk was 10-40 times the serum level. Thus in milk samples collected from 29 mothers within 1 wk and from 46 mothers 3 mo. postpartum the levels of iCT were, respectively, 2.46 .+-. 0.99 ng/ml (mean .+-. SD) and 0.58 .+-. 0.08 ng/ml. Of the 29 mothers, 8 delivered milk at 2 occasions, 1-2 and 4-6 days after delivery. There was a significant decline of iCT by about 20% during this period. One mother delivered milk for 2 mo. During the 1st wk after delivery the iCT decreased from 1.4 to 0.5 ng/ml and after that the iCT content remained rather constant. The level of Ca2+ was correlated to iCT the 1st wk postpartum (r = 0.72 P < 0.01) but not in milk samples obtained after 3 mo. The Mg concentration was weakly correlated to iCT during the 1st wk postpartum (r = 0.37 P < 0.05). There was no correlation between iCT and the total Ca level nor to the Zn concentration. The high concentration of iCT in milk compared to serum suggests a local production of iCT within the mammary gland or a specific transport and concentration mechanism.