Whole body protein turnover in aging man

Abstract

To explore the effects of aging on dynamic aspects of whole body protein metabolism in man, the 15N-glycine infusion method of Picou and Taylor-Roberts was used to estimate rates of total body protein synthesis and breakdown in both young adults and elderly subjects. Nine healthy elderly subjects, 4 male and 5 female, 65–91 yr old, participated in the study. Results obtained with 4 young men and 4 young women, 18–25 yr old, were used for comparative purposes. Total body protein synthesis and breakdown rates, per day and per unit body weight per day, were lower in women than in men and significantly lower in elderly women than in young women. Urinary creatinine was used to estimate muscle mass, and whole body 40K to calculate body cell mass. Whole body protein synthesis and breakdown rates, per unit creatinine, were higher in the elderly than in the young adults. Expressed per unit body cell mass, the rates were higher in elderly men than in young men, and a similar, but not statistically significant, difference was observed between elderly and young women. From these results it appears that whole body protein synthesis declines with age in man and is associated with the loss of body cell mass. There is also a redistribution in the pattern of whole body protein synthesis and breakdown as aging progresses, with the visceral organs making a progressively greater contribution to whole body protein metabolism than the skeletal musculature.