Phosphorus and proton magnetic resonance spectroscopic studies on the relationship between transparency and glucose metabolism in the rabbit lens

Abstract

We report the results of a series of nuclear magnetic resonance (NMR) experiments designed to investigate the relationship between particular aspects of glucose metabolism and cataract formation in the rabbit lens. The glucose metabolism of the rabbit lens incubated in TC-199 medium containing 5·5 m m glucose, in glucose-deficient medium, and in modified Earle's medium containing 5·5 m m glucose devoid of NaCl, is examined in conjunction with the assessment of lens transparency. Significant age-dependent differences in the phosphorus metabolite profile and in hexosemonophosphate shunt flux, as measured by NMR, were observed in lenses incubated in TC-199 medium containing 5·5 m m glucose. Incubation in glucose-deficient medium for 8 hr results in significant increases in the levels of inorganic phosphate and phosphomonoesters, and decreases in ATP and l-α-glycerolphosphate. These levels regain near-normal values after 24 hr incubation in control medium containing 5·5 m m glucose. By contrast, shunt flux is three times the basal level during the recovery period. Lens clarity, as assessed by slit lamp micrography, was maintained throughout the duration of the experiment. Incubation of adult and juvenile lenses for 18 hr in Earle's medium (pH 7·4 or 9·2) containing 5·5 m m glucose, and no NaCl, results in uniform lenticular opacification within 18 hr and changes in ultrastructure of the epithelial and cortical lens fiber cells. No statistically significant change in the NMR visible phosphorus metabolite profile or intralenticular pH is observed for the adult rabbit lens relative to a lens incubated under control conditions. For the juvenile rabbit lens, small, but statistically significant differences in the levels of dinucleotide and uridinediphosphoglucose were observed. Shunt flux, in contrast, is increased two-fold. These results demonstrate that the NMR visible phosphorus metabolite profile of the lens does not necessarily correlate with transparency, and that hexosemonophosphate shunt activity provides a sensitive measure of prior or current lenticular stress.