Longitudinal (T1) relaxation times of phosphorus metabolites in the bovine and rabbit lens.

Longitudinal (T1) magnetic relaxation times for the major phosphorus-containing metabolites present in the bovine and rabbit lens under organ culture conditions and in the bovine and rabbit globe have been determined. Significant differences in T1 for the major phosphorus metabolites in each case are observed, as well as for the same metabolite in the two species examined. Species-dependent lens hydration may account, in part, for these differences. Because of the requirement for rapid repetitive pulsing for the attainment of optimum signal collection efficiency by the Fourier transform nuclear magnetic resonance method, significant differential saturation of metabolite resonance intensities occurs in circumstances where appreciable differences in T1 relaxation times are present, which, unless corrected, leads to erroneous determinations of relative metabolite levels. The net effect of assessing relative metabolite levels in terms of the percentage of total phosphate signal, without a correction for T1 discrimination, is to underestimate metabolites with a long T1 (sugar phosphates) and overestimate those metabolites with a short T1 (ATP). Individual metabolite T1 discrimination factors are calculated from integrated areas of spectra acquired using short and long repetition times as well as from metabolite T1 values. They are then employed, for the first time, for the correction of 31P-NMR spectra of bovine and rabbit lenses. Corrected spectra provide relative metabolite levels for lenticular ATP which are in excellent agreement with values determined by chemical and enzymatic assays.