Kinetics of Saturable Transport across the Blood—Brain Barrier

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Abstract
This article is concerned with the extension of the Renkin-Crone model to a case of saturable transport across the blood–brain barrier, i.e., when the apparent permeability-surface area product is concentration dependent. A well-mixed tissue compartment is assumed, together with a simple symmetric saturable transport system. A computation scheme, or algorithm, is described that allows the calculation of arteriovenous differences and net influx rates for parent substance and tracer in terms of arterial and tissue concentrations of each, the transport maximum Tmax, the half-saturation constant Kt, and plasma flow rate. The scheme was devised initially for the analysis of experiments in which the parent substance was not in a steady state and in which tracer backflux from tissue to capillary was significant.