Biology of Reproduction, Vol 12, 275-283, Copyright © 1975 by Society for the Study of Reproduction

The Role of Carnitine in Spermatozoan Metabolism: Substrate-Induced Elevations in the Acetylation State of Carnitine and Coenzyme A in Bovine and Monkey Spermatozoa

¹ Reproductive Physiology Section, Oregon Regional Primate Research Center, Beaverton, Oregon

To determine the metabolic role of carnitine in bovine epididymal and rhesus (Macaca mulatta) ejaculated spermatozoa, we studied the effect of substrate utilization on the acylation state of carnitine and on the acetylation state of carnitine and CoA. The acetylcarnitine content of bovine spermatozoa incubated in fructose, glucose, pyruvate, lactate, acetoacetate. -OH butyrate, and acetate was significantly higher than that of nonincubated cells or cells incubated without substrate. In bovine cells incubated with palmitate or without substrate, however, the levels of acetylcarnitine and long-chain acylcarnitine remained relatively unchanged. In freshly ejaculated monkey spermatozoa, about 45% of the acid-soluble carnitine was in the acetylated state. This value dropped to about 15% in cells incubated without substrate and increased to about 70% in cells incubated with glucose or fructose. Total acid-soluble CoA concentrations in bovine and monkey spermatozoa were 0.96 and 2.0 nmoles/10⁹ cells, respectively; when the cells were incubated in fructose or glucose, the increases in the acetylation state of CoA were similar to those in carnitine. Thus the acetylation of carnitine plays an important role in normal spermatozoan metabolism and the carnitine: carnitine acetyltransferase system appears to buffer against rapid changes in the concentration of acetyl-CoA.