Exogenous lactate is essential for metabolic activities in isolated rat spermatocytes and spermatids

Spermatocytes and round spermatids were isolated from rat testis and the effects of addition of 3.3 mM-glucose and 6 mM-DL-lactate to the incubation medium on the morphology, oxygen consumption and incorporation of uridine and amino acids of these cells were investigated. Addition of lactate to isolated germ cells increased O2 consumption 1.8-fold and incorporation of precursors of RNA and protein by at least 5-fold. The amino acid incorporation into spermatocytes and spermatids was irreversibly decreased after a preincubation for at least 5 h or 70 min respectively in the absence of lactate, indicating degeneration of the germ cells. In the presence of lactate, however, spermatocytes maintained their morphological integrity for at least 24 h. Addition of glucose to isolated germ cells had no effect on any of the parameters investigated. It is concluded that isolated spermatocytes and round spermatids may utilize lactate, perhaps secreted by Sertoli cells, as the main source of energy.