Glucose and acetate metabolism by ram, bull, dog and fowl spermatozoa

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Abstract
Ram, bull, dog and fowl spermatozoa metabolize acetate and glucose, but there are differences between the species. Ram and bull spermatozoa oxidize acetate in preference to glucose, but with dog spermatozoa the reverse is true. The preferential oxidation of acetate by ruminant spermatozoa indicates their greater ability to activate acetate in the presence of pyruvate, an alternative precursor of acetyl-CoA. Ram, bull and dog spermatozoa break glucose down to lactic acid almost quantitatively under aerobic conditions, but with fowl spermatozoa there is an accumulation of fructose as well as lactate. There was no evidence of pentose-shunt activity from the labelled-carbon dioxide ratios (1.00-1.18) obtained after incubating spermatozoa with D-[6-14C]glucose and with D-[1-14c]glucose. The labelled-carbon dioxide ratios (0.83-1.10) obtained with [1-14C]acetate and with [2-14c]acetate as substrates indicate that ram, bull and dog spermatozoa have negligible synthetic activity and possess only catalytic amounts of C3 or C4 intermediates. The corresponding ratio (2.25) for fowl spermatozoa suggests an influx of unlabelled tricarboxylic acid-cycle intermediates. With labelled acetate and glucose it has been possible to obtain an accurate estimate of the endogenous oxidation in spermatozoa in the presence of an exogenous substrate. The endogenous contribution was less than the exogenous for all species except the fowl.