Lactate Dependent Protein Synthesis in Round Spermatids from Rat Testes

Lactate (20 mM) markedly increased protein labeling of round spermatids (steps 1-8) from rat testes. The stimulatory effect of lactate on protein labeling was also observed to some degree in spermatocytes and late spermatids (steps 13-16), but not in Leydig cells and 7 day-old testis cell suspznsions. In the lactate-treated spermatids, 51 % of the labeled proteins was found in the water-soluble fraction (the 105,000 ×g 1 hr supernatant), whereas only 21%, in the control cells. The labeled proteins did not break down for at least 90 minutes in the presence of lactate. Actinomycin D (20 μg/ml) had no effect on [3 H]leucine incorporation into the water-soluble proteins of spermatids, while labeling of the water-insoluble proteins (the 105,000 ×g 1 hr pellet) was decreased by 23%. These findings suggest that the round spermatids might be the most susceptible for the lactate-induced stimulation of protein synthesis among various types of testicular cells, and that lactate increases the synthesis of water-soluble proteins which may be regulated in the translational level of protein synthesis.