APPLICATION OF MAXIMAL REMOVAL RATE OF INDOCYANINE GREEN TO THE DETERMINATION OF HEPATIC FUNCTIONAL MASS IN CONSCIOUS RATS

We established a versatile method for the measurement of indocyanine g reen maximal removal rate (ICG Rmax) to detect hepatic functional mass in conscious rats using a repeated blood sampling procedure. On inves tigation of the optimal technical conditions, the appropriate intraven ous administered doses of ICG were 2.5, 5, 10 or 20 mg/kg, and the bes t blood collection times for calculating plasma half-life at these dos es were immediately before, and 4, 7 and LO min after ICG injection. T he interval among the respective ICG injections was more than 4 hr. In hepatectomized rats, the ICG Rmax value was reduced to about 50% and 20% of sham-operated rats in mean 2/3 and 4/5 liver resections, respec tively, suggesting that it would almost extrapolate to hepatic survivi ng reserves under these experimental conditions. In rats treated subcu taneously with carbon tetrachloride (CCl4, 0.1 and 0.25 ml/kg) thrice weekly during a 17-week period (120 days), a decrease in ICG Rmax valu e did not correlate with increases in serum alanine transaminase (ALT) , alkaline phosphatase (ALP) and total bilirubin values throughout the experimental periods. However, the reduced ICG Rmax well correlated w ith decreases in serum albumin and cholinesterase (CHE) values from da y 50. Histological examinations in the liver revealed that nodules of hepatocytes were separated by thick fibrous bands, defining the typica l aspect of cirrhosis on day 30 to 90. These results suggest that the measurement of ICG Rmax is a valuable tool for the estimation of hepat ic functional integrity in rats.