31P-NMR determination of phosphomonoesters in relation to phospholipid biosynthesis in testis of the rat at different ages.

Changes in the phosphomonoester (PM) peak, as observed in in vivo 31P-NMR spectra, are often attributed to changes in phospholipid synthesis and therefore to changes in cell proliferation. However, this technique provides information about the absolute size of the phosphomonoester pool rather than its turnover rate. To investigate whether there is a good correlation between changes in PM concentration and its turnover rate, we studied the turnover rate of the two major PM compounds, phosphocholine and phosphoethanolamine, in rat testes at different stages of testis development. [3H]Choline and [3H]ethanolamine were injected intraperitoneally into rats at the age of 3, 6 and 13 weeks, respectively. Phosphorylation of these compounds and their incorporation into phospholipids, were followed up to 6 h after injection of the phospholipid precursors. When these data were compared with the changes observed in the in vivo 31P-NMR PM peak, the concentration of the PM compounds appeared to correlate linearly, both with the conversion of choline into phosphocholine, as well with the rate of phospholipid synthesis, and therefore with the rate of cell proliferation. Hence, it is suggested that cell proliferation can be monitored by determining the changes in the PM peak that is observed in in vivo 31P-NMR spectra.