PLASMA PROTEIN SYNTHESIS BY TISSUE SLICES FROM PREGNANT AND LACTATING RATS

The capacity of the liver to synthesize albumin and transferrin and the spleen to synthesize transferrin and γG was measured by incubating tissue slices from pregnant and lactating rats with [14C]leucine and determining the incorporation of radioactivity into specific albumin, transferrin and γG immunoprecipitates. Mammary gland synthesis of transferrin and γG was also measured during lactation in the same way. Pregnancy was associated with a marked increase of 14C-incorporation by liver slices into albumin and a lesser increase of incorporation into transferrin when compared with slices from non-mated control rats. Incorporation into both proteins returned to the control levels by the fifth day of lactation. There was no change of 14C-incorporation by spleen slices into transferrin or γG during pregnancy or lactation relative to the controls. The incorporation of [14C]leucine into transferrin by mammary tissue fell from relatively high values on lactation day No. 1 to minimal values on day No. 5 and then rose again steadily to be maximal on day No. 20. At this time incorporation per unit weight of tissue was 1.15 times as great for mammary gland as for liver, and the incorporating capacity of all the mammary tissue was 1.5 times as great as the whole liver. The incorporation per unit weight of mammary tissue into γG remained relatively constant throughout lactation at a rate which was about 10 % that of the spleen. © 1969.