Non-invasive measurement of steady-state vitreous lactate concentration

The cellular events leading to the proliferation of new preretinal blood vessels into the vitreous are unknown. It has been hypothesized that a metabolic trigger, such as increased lactate concentration, induces ambient growth factors to initiate this neovascularization. However, this hypothesis has not been tested in vivo because non-invasive methods for measuring vitreous lactate concentration have not been available. In this study, we identified lactate as the dominant resonance in normal rabbit vitreous using a water-suppressed, localized proton NMR method; negligible spectral contamination from lipid, alanine and threonine was demonstrated. The steady-state vitreous lactate concentration in vivo was 11.3 +/- 4 mM (mean +/- SD, n = 7 eyes) which was not statistically different (p = 0.498) to the enzymatically determined lactate content in vitreous from a parallel group of animals [12.1 +/- 0.6 mM (n = 6 eyes)]. Non-invasive measurement of steady-state vitreous lactate concentration using localized proton NMR represents the necessary first step in understanding the role of lactate in neovascularization.