CHANGES IN CARBOHYDRATE-METABOLISM OF TESTICULAR GERM-CELLS DURING MEIOSIS IN THE RAT

A study was undertaken to estimate the activities of the key enzymes o f glycolysis, the pentose phosphate pathway and the tricarboxylic acid (TCA) cycle in purified rat spermatocytes and spermatids, which have been shown to die in glucose-containing medium and require lactate/pyr uvate for maintaining normal ATP concentrations. The aim was to elucid ate the changes in the glycolytic and oxidative potential of germ cell s undergoing meiosis. Pachytene spermatocytes and round spermatids fro m adult rat testis were purified to similar to 90% purity by trypsin d igestion followed by a combination of centrifugal elutriation and Perc oll density gradient centrifugation. After the purity and viability of these cells had been established, their contents of hexokinase, phosp hofructokinase, lactate dehydrogenase (LDH) and LDH-X of glycolysis, g lucose 6-phosphate dehydrogenase of the pentose phosphate pathway and citrate synthase, aconitase, malate dehydrogenase and 2-oxoglutarate d ehydrogenase of the TCA cycle were estimated. These enzymes were also estimated in epididymal spermatozoa for comparison with the testicular germ cells. The results indicate greater activity of glycolytic and p entose phosphate pathway enzymes in spermatocytes than in spermatids, which exhibited greater activity of TCA cycle enzymes than the former. The difference in activity was statistically significant for most of the enzymes studied. In contrast, spermatozoa exhibited markedly great er activity of glycolytic enzymes and significantly lower activity of pentose phosphate pathway and TCA cycle enzymes than did the testicula r germ cells. We conclude that the unusual dependence of spermatids ex clusively on lactate may be due to their lower glycolytic potential, w hereas spermatocytes with comparatively greater glycolytic activity ha ve an intermediate dependence on lactate and are therefore able to uti lize lactate, pyruvate, or both, while retaining a better ability to u tilize glucose. Spermatozoa with the greatest glycolytic potential and the lowest TCA cycle activity appear to be 'programmed' to utilize ex clusively glucose/fructose for energy.