Penetration of [ 3 H] Tiazofurin Into Guinea Pig Eye by a Saturable Mechanism

Abstract

This study investigated the transport of tiazofurin (2-ß-D-ribofuranosyl thia-zole-4-carboxamide) across the blood-aqueous humor barrier, using the vascular perfusion method in the guinea pig. Volume of distribution (V_d) of [³H] tiazofurin increased almost linearly in time, from 4% of its plasma concentration at 3 min to 10% after 12 min of perfusion. Unidirectional transport constant, K_in was 7.01 ± 1.06 × 10^-3 ml/min/g. These results indicate that tiazofurin penetrates the aqueous humor to a considerable extent. Addition of unlabelled tiazofurin to the perfusing medium caused a significant decrease in the uptake of [³H] labelled tiazofurin (K_in = 2.60 ± 0.91 × 10^-3 ml/min/g). Therefore, penetration of tiazofurin from blood into aqueous humor seems to be a saturable process with a diffusional component that cannot be disregarded. Such findings could be of considerable importance since this molecule is known to affect tissue metabolism.