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AN EVALUATION OF THE RESPIRATORY CAPACITY OF HUMAN SPERMATOZOA

Summary.: The level of human sperm respiration in semen and in artificial media has been estimated by manometric and radiochemical techniques. Our results show that the respiration is small, exhibiting rates that rarely exceed 1 to 2 µl/10⁸ cells/hr. These low Zo₂ values and the limited sensitivity of the manometric apparatus stress the point that pooled specimens with high cell concentrations must be used in order to obtain reliable estimates of oxygen consumption. Attention is also drawn to the fact that measurements of oxygen uptake by cells in whole semen are further complicated by the high rates and variability of oxygen absorption by seminal plasma and that small errors in the estimation of this absorption can lead to substantial errors in estimates of cellular oxygen uptake. Although isotopic measurements of respiration are more sensitive than manometric techniques, some reserve is also required when interpreting results based on ¹⁴CO₂ evolution alone. Experiments with [U-¹⁴C]glucose and [6-¹⁴C]glucose indicate that the carbon atoms of glucose are not converted to CO₂ in an identical manner. The higher rates of ¹⁴CO₂ produced from the metabolism of uniformly labelled glucose suggest that a portion of the glucose molecule may be converted to CO₂ through non-oxidative pathways. In view of such a possibility, the ability of washed cells and whole semen to convert [6-¹⁴C]glucose into labelled CO₂ provides less equivocal radiochemical evidence than that previously reported for true respiratory activity in human sperm cells. High phosphate concentrations inhibit the conversion of glucose to carbon dioxide. It is suggested that this may represent the presence of competing reactions for limiting intermediates involved in glycolytic and respiratory pathways. We have also described the use of the rapid Millipore filtration technique to follow glucose uptakes and incorporation into acid-insoluble (lipid) components of sperm cells. Uptake into acid-insoluble compounds is rapid and represents a substantial portion of the radio-active glucose that is retained by cells. The potential usefulness of this method to measure endogenous lipid turnover and the role of cellular lipid in endogenous respiration is also considered.