Hepatic, renal, and total body galactose elimination in the pig

Galactose elimination capacity is used as a quantitative measure of liver function on the assumption that galactose elimination outside the liver is negligible or easily corrected for. The relationship between hepatic and extrahepatic removal of galactose was studied in anesthetized pigs during quasi-steady-state conditions by continuous infusion of galactose. The hepatic removal approximated a constant [maximal velocity = 585 +/- 41 mumol/min, Michaelis constant (Km) = 0.24 +/- 0.07 mmol/l, mean +/- SE, n = 20]. The renal removal was less than the amount filtered, showing maximal tubular reabsorption (Tm 178 +/- 3.0 mumol/min, Km 3.8 +/- 0.9 mmol/l, n = 20). Metabolic conversion of galactose in the kidney was not demonstrable. At all concentrations studied (0.4-5.8 mmol/l), total galactose elimination from the body exceeded the sum of hepatic and renal elimination by approximately 100 mumol/min, independent of the concentration. At blood concentrations usually used for clinical estimation of the galactose elimination capacity (approximately 4 mmol/l), hepatic removal in the pig accounted for 55% and renal removal for 30% of total removal; 15% of removal occurred in other organs. We conclude that estimation of the hepatic galactose elimination capacity from whole body elimination curves requires correction for renal removal of galactose.