The Na(+)-dependent transport of L-alanine into liver plasma membrane vesicles isolated from young, 2-month-old, and aged, 24-month-old, normal and turpentine-treated rats, to induce an aseptic inflammatory condition and the acute-phase response, was studied. In old rats, alanine transport maintained the same features observed in young controls, being strictly Na(+)-and electrical potential-dependent. However, old rats showed a twofold increase in the Vmax value for alanine uptake compared with young controls, the affinity constant (Km) remaining unmodified. Four hours after turpentine treatment, the Vmax value of alanine transport in young rats was 2.5-fold over that observed in untreated controls. In contrast, old turpentine-treated rats demonstrated only slight increases in this value, compared to untreated old controls. In both young and old turpentine-treated rats, the Km values of alanine transport remained almost unmodified. Since dysregulation of interleukin 6 (IL-6) gene expression, a multifunctional cytokine that is proving to be a major contributor to the acute phase response, occurs with advancing age in different animal species, the increased alanine transport across liver plasma membrane vesicles observed in old "normal" rats might be related to an increased IL-6 production, inducing an acute phase protein synthetic activity, in these animals.