Relative Dispersions of Intra-albumin Transit Times across Rat and Elasmobranch Perfused Livers, and Implications for Intra- and Inter-species Scaling of Hepatic Clearance using Microsomal Data

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Abstract
It is recognized that vascular dispersion in the liver is a determinant of high first‐pass extraction of solutes by that organ. Such dispersion is also required for translation of in‐vitro microsomal activity into in‐vivo predictions of hepatic extraction for any solute. We therefore investigated the relative dispersion of albumin transit times (CV2) in the livers of adult and weanling rats and in elasmobranch livers. The mean and normalized variance of the hepatic transit time distribution of albumin was estimated using parametric non‐linear regression (with a correction for catheter influence) after an impulse (bolus) input of labelled albumin into a single‐pass liver perfusion. The mean±s.e. of CV2 for albumin determined in each of the liver groups were 0·85 ± 0·20 (n = 12), 1·48 ± 0·33 (n = 7) and 0·90 ± 0·18 (n = 4) for the livers of adult and weanling rats and elasmobranch livers, respectively. These CV2 are comparable with that reported previously for the dog and suggest that the CV2 of the liver is of a similar order of magnitude irrespective of the age and morphological development of the species. It might, therefore, be justified, in the absence of other information, to predict the hepatic clearances and availabilities of highly extracted solutes by scaling within and between species livers using hepatic elimination models such as the dispersion model with a CV2 of approximately unity.

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