KINETICS OF HEPATIC AMINO-NITROGEN CONVERSION IN AGING MAN

Previous studies have shown that hepatic function, quantitatively meas ured by dynamic liver function tests, progressively declines with agei ng. Urea synthesis is a specific process taking place in the liver; a reduced urea synthesis in response to a protein-rich metal has previou sly been demonstrated in the elderly, but the process has never been s tandardized in relation to amino acid supply. We measured the hepatic conversion of alpha-amino nitrogen into urea nitrogen in response to a lanine infusion in 32 subjects, with normal routine liver and renal fu nction tests and without evidence of previous hepatic disorders, belon ging to three different age-groups (less than or equal to 55 years, 56 -70, greater than or equal to 71). The functional hepatic nitrogen cle arance was reduced on average by 20% in subjects aged 56-70 years, and by 30% in subjects over 70 years old in comparison to the age group u nder 55 years (ANOVA: P=0.0001), and significantly correlated with age (r=-0.684). No sex differences were observed on the effects of age on hepatic clearance. Also, liver volume, measured by ultrasonography, w as reduced with advancing age, but the age-related decrease in hepatic nitrogen conversion was not primarily dependent on decreased liver vo lume. The measurement of functional hepatic nitrogen clearance has alr eady been validated as a quantitative liver function test in clinical hepatology. In keeping with previous studies, the age-related deceline in hepatic nitrogen conversion points to a decreased functional capac ity of the ageing hepatic parenchyma.