Plasma and hepatic binding of indocyanine green in guinea pigs of different ages.

Binding of indocyanine green (ICG) to the proteins in plasma and bile of guinea pigs ranging in age from 1 day old to adult was studied. The ICG in plasma was almost totally bound to the protein and there was no significant difference in the binding between newborn and adult animals. Binding of ICG to biliary protein was similar in all age groups. Particulate fractions of liver from adult guinea pigs had a higher ICG binding capacity than that from the newborn at all concentrations tested. The uptake of ICG by liver slices involved mostly active processes. The slice-to-medium (S/M) ratio of ICG was lowest in liver preparations from the newborn; however, the S/M ratio for adult animals was lower than that for 10-day-old animals. Liver slices from adult guinea pig showed the fastest ICG efflux rate, and the efflux rate with liver slices from the newborn was the slowest. Processes of hepatic uptake and release of ICG were incompletely developed in the newborn guinea pig.