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.