In vivo entry of glucose analogs into lens and cornea of the rat.

Methods were developed for the in vivo estimation of rate constants for transport from blood to aqueous and subsequently into lens and corneal water compartments. Glucose transport was characterized with the nonmetabolized radiolabeled glucose analogs (14C)-L-glucose (L-glu) and (3H)-3-O-methyl-D-glucose (mD-glu) that are considered to enter the ocular humors by passive and facilitated diffusion respectively. The glucose analogs were introduced simultaneously as a bolus into a femoral vein in anesthetized normal rats and the subsequent appearance in ocular humors, lens, and corneal tissue were determined at various time periods after the initial introduction. Results indicate that mD-glu transport into lens is faster than L-glu with mD-glu concentration in lens water approaching steady state aqueous humor concentrations. Estimated steady state L-glu concentrations in lens remain well below aqueous concentrations, and entry into lens is seen to be slow with interior regions probably inaccessible to this passive marker. This study gives in vivo support to the previous in vitro studies, which have suggested a facilitated diffusion mechanism for glucose entry into lens. Corneal steady state concentrations of L-glu and mD-glu are higher than in either plasma or aqueous humor from which they are thought to have originated via the endothelium. Transport of both L-glu and mD-glu into cornea is very fast, and entry rate constants demonstrate no clear statistical difference, thereby suggesting the absence of a stereospecific mechanism. The results indicate that glucose transport is not by simple or facilitated diffusion or by stereospecific active transport.(ABSTRACT TRUNCATED AT 250 WORDS)