Metabolism of pachytene primary spermatocytes from rat testes: pyruvate maintenance of adenosine triphosphate level.

Pachytene primary spermatocytes were prepared and examined for energy metabolism. When the cells were incubated with various substrates (glucose, fructose, pyruvate and lactate) to measure their utilization of substrates and the degree of ATP synthesis, spermatocytes were observed to use pyruvate as much as lactate, but in amounts much greater than those of glucose or fructose. Pyruvate and lactate maintained ATP levels in spermatocytes, while only lactate did in round spermatids and residual bodies. Pyruvate (5 mM) did not inhibit ATP synthesis from lactate in spermatocytes, differing from its behavior in spermatids. Pyruvate was oxidized in the Krebs cycle for further oxidative phosphorylation and was not altered by addition of glucose. Pyruvate and lactate were interconverted, but the intracellular level of pyruvate remained unchanged (approx. 0.2 mM) when either pyruvate or lactate was added to the medium. The maximal activity of lactate dehydrogenase (LDH) of spermatocytes occurred at 0.3-0.7 mM pyruvate, and this enzyme promoted the conversion of pyruvate to lactate rather than the reverse reaction. In addition, activity assays of 11 glycolytic enzymes and concentration assays of glycolytic intermediates showed a possible regulatory role for glyceraldehyde-3-phosphate dehydrogenase (GA3PDH) in glycolysis. These observations suggested that spermatocytes differed strikingly from spermatids with respect to energy metabolism, even though glycolysis in the two categories of germinal cells was presumably regulated by GA3PDH.