Real-time hexose monophosphate shunt activity in light- and dark-adapted rabbit retinas

Correlation proton nuclear magnetic resonance spectroscopy was performed on light- and dark-adapted rabbit retinas to elucidate real-time hexose monophosphate shunt (HMPS) activity. Light significantly stimulated retinal HMPS initially, which consumed 17% more glucose than that in dark-adapted retinas. The glucose consumption eventually declined to 16% of total, the baseline level, after 60 min of light exposure. In contrast, dark-adapted retinas showed an initial HMPS activity of 29% total glucose consumption, which declined to the basal level after 40 min. Lactate production appeared stable in both sets of retinas. Tert-butyl hydroperoxide (1 mM) also stimulated the shunt; however, a combination of light-adaptation and tert-butyl hydroperoxide did not stimulate the shunt additively. These data indicate that the retina has limited HMPS capacity.