Investigations on the motility of human spermatozoa in a defined medium in the presence of metabolic inhibitors and of carnitine.

When washed human sperm were incubated in a modified Krebs-Ringer buffer solution in the absence of exogenous metabolizable substrates at 30 degrees C they maintained progressive motility for at least six hours. Under these conditions the spermatozoa apparently utilize endogenous substrates but addition of exogenous substrates (glucose, fructose, acetate, short-chain fatty acids, branched chain amino acids) did not affect the % progressive motility or % total motility of the cells. The phospholipase inhibitors, quinacrine and Upjohn No. 1002, inhibited progressive motility when added to sperm utilizing endogenous substrate, and subsequent addition of oxidative or glycolytic substrates did not reverse the inhibition. In contrast, the inhibition by KCN of progressive motility based upon utilization of endogenous substrate was reversed upon addition of glycolyzable compounds (glucose or fructose). The addition of carnitine or its acetyl-, propionyl-, isobutyryl-, valeryl- or isovaleryl esters did not consistently affect progressive or total motility of sperm samples. The inhibitor, octylsulfobetaine, inhibited sperm motility at a concentration higher than that required for inhibition of carnitine acetyltransferase or translocase activity. On the basis of these results it does not appear that exogenous carnitine has an effect on the motility of human sperm incubated under the conditions described here.