Sex differences in nitrogen balance following marrow grafting for leukemia

A sex difference in nitrogen balance was investigated in 40 adults, 21 men and 19 women, undergoing chemoradiotherapy and marrow transplantation for leukemia and receiving total parenteral nutrition. Twenty-four hour collections of urine and mixed urine-stool were analyzed for total nitrogen daily through day 14 posttransplant. Nitrogen balance, corrected for changes in blood urea nitrogen, decreased significantly over time (p less than 0.005) in both men and women, but men experienced a greater negative nitrogen balance during the time period (p less than 0.001). Mean daily nitrogen balance in men was -6.0 g for week 1 and -9.2 g for week 2, corresponding to -3.3 g and -5.6 g in women for week 1 (p less than 0.005) and 2 (p less than 0.01), respectively. The differences remained after controlling for stress level and adjusting for total calorie intakes. There were no differences in age, disease status, or nitrogen intakes per kg ideal body weight, and no effects on nitrogen balance by arm muscle area at admission, cyclosporine use, or the branched-chain amino acid content of the parenteral solution. The average rise in 3-methylhistidine excretion was 23% in men and 11% in women. These results suggest higher per kg nutrient needs in males during stress and may indicate differing metabolic responses to stress. The possibility of gender differences should be considered in research evaluating nitrogen metabolism during severe stress.