Ceruloplasmin is found in milk and amniotic fluid and may have a nutritional role

Ceruloplasmin is a copper binding, alpha(2)-globulin of blood plasma, made by the liver but also expressed by some other secretory tissues, including the choroid plexus of brain and the mammary gland. During studies of neonatal copper transport in the rat, it was determined that amniotic fluid contains ceruloplasmin, based on the presence of azide-inhibitable p-phenylene diamine (pPD) oxidase activity eluting like serum ceruloplasmin in ion exchange chromatography. When Cu-67-labeled (serum-derived) ceruloplasmin was injected into the amniotic sac of fetal mts near term, there was a rapid transfer of the Cu-67 to the liver and carcass. Uptake of injected ionic C-67(II) was less rapid. Subsequently, the presence of ceruloplasmin in milk was sought and confirmed in several species, using enzymatic and immunologic methods. Based on pPD oxidase activity inhibitable with N-3-, milks from humans, cows, and pigs all contained similar concentrations of ceruloplasmin and more than in mouse milk There was no correlation between milk and serum ceruloplasmin oxidase activities among the species. As in amniotic fluid, ceruloplasmin was calculated to account for a substantial portion of the total copper present. A systematic study of non-colostrum human milk indicated by immunoassay that mean ceruloplasmin concentrations were 4.7 mg/L and copper concentrations 9.3 mu mol/L during the first 5 days, post-partum. These values dropped about 50% (to 2.3 mg/L and 4.3 mu mol/L, respectively) by the end of the first month of lactation. Ceruloplasmin concentrations of about 2 mg/L were maintained during long-term breastfeeding, although total copper concentrations continued to decline. Newborn rats fed Cu-67 in milk preferentially absorbed ceruloplasmin-derived copper over ionic copper mixed with milk whereas 4-week-old weanling rats absorbed both forms equally well. It is concluded that ceruloplasmin is a significant copper binding component of milk and amniotic fluid and more nutritionally available than other ingested copper in the perinatal period. (C) Elsevier Science Inc.