[Biosynthesis and secretion of ceruloplasmin by rat mammary cells during lactation].

Some peculiarities of rat milk ceruloplasmin (CP) biosynthesis have been analysed. Electrophoretic and immunoelectrophoretic data suggest that rat milk contains up to 20 mg/100 ml of CP. Rat milk CP is represented by a single molecular form whose molecular mass, enzymatic activity and antigenic properties are fully identical with those of serumal CP. According to the dot hybridization date, the CP-mRNA content in rat mammary cells is about ten times as low as that in adult rat liver. Analysis of polyribosomal RNA by blot hybridization of RNA-cDNA revealed that rat mammary CP-mRNA is represented by a single molecular form, 3.5 kb in length, whose molecular mass is identical with that of the predominant CP-mRNA of rat liver. The dynamics of secretion of the de novo synthesized CP into rat milk indicates that the CP synthesis and secretion occur independently of the serumal CP. In vitro and in vivo pulse labelling studies demonstrated that rat milk CP is synthesized and secreted by rat mammary cells.