ALBUMIN, TRANSFERRIN AND GAMMA-GLOBULIN METABOLISM DURING LACTATION IN THE RAT

The turnover of rat serum albumin, transferrin and γ-globulin and their transfer to the milk was studied following injection of radioiodine-labelled purified proteins to rats on the 2nd, 9th and 17th days of lactation. The concentrations of the three proteins were also measured in maternal serum, milk whey and the serum of the suckling young. The concentrations and relative and absolute rates of turnover of each protein in maternal serum changed very little with progression of lactation. The concentration of transferrin in whey increased greatly as lactation progressed, while the concentrations of the other two proteins remained constant. The ratio of whey protein-bound radioactivity to maternal serum activity was constant for each protein at the three stages of lactation. The specific activity of whey albumin and γ-globulin also remained constant at 100 and 85 per cent respectively of the maternal serum values, while the transferrin specific activity fell from 100 per cent the maternal serum value in early lactation to 25 per cent of this value late in lactation. It is concluded that all of the albumin and most of the γ-globulin of rat whey is derived from the blood plasma, while an increasing amount of transferrin up to 75 per cent in late lactation, and a little γ-globulin is synthesized in the mammary gland.