Influence of Temperature on Lactate Utilization by Round Spermatids from Rat Testes. (Temperature/lactate/spermatids/rat/oxidative phosphorylation)

Abstract

Rotenone-sensitive "CO, formation from [Wllactate and oxygen consumption by round spermatids were found to be greater at elevated temperatures than at 34°C. More than 96% of the total radioactivity of the metabolized ["Cllactate was recovered in the released CO, and the acid soluble fraction of the cells. There was practically no incorporation of ["Cllatctate into the lipid, nucleic acid, and protein fractions. Intracellular level of ATP in spermatids was enhanced in the presence of lactate (20 mM) at 34°C (scrotal temperature), whereas it was decrease at 37°C (body temperature). However, this was reversible when the cells were transferred from the elevated temperature to 34°C. It was also found that oxygen consumption and CO, production were increased at 34°C by 2, 4-dinitrophenol (DNP), but decreased by oligomycin. On the other hand, oligomycin and DNP had no etrect on oxygen consumption and "CO, formation at the elevated temperature.These findings provide evidence that lactate utilization by spermatids is coupled with oxidative phosphorylation at scrotal temperature, but becomes uncoupled at elevated temperature, although more lactate is consumed.In the most mammals, the testis is positioned in the scrotum which provides an ambient temperature lower than the abdomen. An increase in testicular temperature has been found to cause a rapid degeneration of the seminiferous tubules and to disturb the normal spermatogenesis (l), but the reason for this remains unclear.The testicular metabolism in rats has been shown to be heavily dependent on glucose (2, 3). Glucose has been reported to stimulate protein synthesis of rat testis tissue (4, 5). Interestingly, oxygen uptake by the tissue of rat testis occurred in the presence of glucose at a maximum rate when the temperature was 37°C (2), but protein synthesis declined at the same temperature (6). Recent studies by NAKAMURA and co-workers (7-9) have shown that lactate is a major substrate for spermatid metabolism in rats. In particular, lactate markedly enhanced protein synthesis of round spermatids via an increase in intracellular level of ATP (8, 9).Experiments described in this paper demonstrate that utilization of lactate by round spermatids from rat testis occurs more at an elevated temperature. However, such an enhanced utilization of lactate at the elevated temperature as described here is uncoupled with oxidative phosphorylation. 265