Specific effects of protein deprivation on thymus and spleen; rates of protein synthesis in lymphocytes derived from thymus,spleen and bone marrow

Young adult male rats (body weight 90 g) were fed for 6 days a low protein (3% casein) diet and compared with rats fed a diet optimal in protein (20% casein). To study the dietary effects of protein, but not energy deficiency, intake of energy per unit body weight was kept constant. Wet weights and DNA content of thymus and spleen organs decreased in the low protein diet group. The in vitro incorporation of 14C-leucine into protein by isolated ribosomes was diminished in thymus by 22% and in spleen by 33% per mg of ribosomal RNA, and per mg of DNA by 43% in thymus and 48% in spleen. Lymphocytes were separated by Ficoll gradients. As compared with controls lymphocyte number from thymus decreased by 90%, that of spleen by 43% and of bone marrow by 20%. The rates of protein synthesis were significantly reduced after protein restriction in lymphocytes of the 3 organs. The strongest effects on the rates of protein synthesis were observed in bone marrow. Reduction in lymphocytes recovered was most pronounced in thymus. The results indicate that malnutrition by protein, but not energy deficiency, elicites specific effects on the 3 lymphocyte producing or containing organs studied.