Glucose concentration profiles of normal and ultraviolet radiation-exposed rabbit corneas

The passage of glucose within the cornea has been thought to occur by passive diffusion processes. However, corneal glucose concentration profiles have not been established to support this notion. While microfluorometric methods of metabolite assay typically have been used as a means of assessing regional brain metabolism, this unique methodology of tissue isolation and metabolite determination has not previously been applied to the cornea. Since this technique permits metabolite quantification on microgram-sized tissue samples, a co-ordinated corneal glucose concentration profile can be obtained. Tissue preparation consisted of liquid nitrogen freezing, cryo-sectioning, and freeze-drying, with storage at -20 degrees C. The sections were thawed under vacuum pump, subsectioned, weighed, and assayed for glucose concentration (by dry weight). This study established a glucose concentration profile of the epithelium, anterior stroma, midstroma, posterior stroma, and endothelium for the normal pigmented rabbit cornea. A glucose concentration profile for UV radiation-exposed rabbit corneas also was documented. The UV radiation glucose profile data indicate the presence of an active transport mechanism capable of delivering glucose into the corneal epithelium against a concentration gradient. The presence of a transport system that 'pulls' glucose through the deeper corneal layers thus would make epithelial integrity important for the maintenance of overall corneal viability.