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

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 one week and from 46 mothers three months post partum the levels of iCT were respectively 2.46 +/- 0.99 ng/ml (mean +/- SD) and 0.58 +/- 0.08 ng/ml. Eight of the 29 mothers delivered milk at two occasions, 1-2 and 4-6 days after delivery. There was a significant decline of iCT with about 20% during this period. One mother delivered milk for two months. During the first week 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 ionized calcium (Ca++) was correlated to iCT the first week post partum (r = 0.72 p less than 0.01) but not in milk samples obtained after three months. The concentration of magnesium was weakly correlated to iCT during the first week post partum (r = 0.37 p less than 0.05). There was no correlation between iCT and the total calcium level nor to the concentration of zinc. 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.