[Acetylcarnitine and spermatozoa: relationship with epididymal maturation and motility in the boar and man ].

The level of carnitine and acetylcarnitine in spermatozoa of boar epididymal origin and of human ejaculates was demonstrated. In the epididymal fluid of boars, the concentration of carnitine (nmol/mg protein) began to increase from 20 in the distal caput to rise progressively to 700 in the distal cauda. By contrast, the carnitine content of spermatozoa only started to increase in the proximal cauda where the concentration of carnitine in the fluid was 200-300 nmol/mg protein, then gradually increased in spermatozoa from more distal sites. The increase in the acetylcarnitine content of spermatozoa paralleled that of the carnitine amount, represented 50% of total carnitine (carnitine + acetylcarnitine) and coincided with the acquisition of progressive motility. In two populations of human seminal spermatozoa selected by migration and characterised by a very large difference in their percentage of progressively motile cells, higher carnitine and acetylcarnitine contents (40%) were found in migrated spermatozoa compared to the residual population. These results suggest that accumulation of carnitine and its metabolite may be an important factor in the acquisition and the maintenance of progressive motility. Measurement of acetylcarnitine content of human seminal spermatozoa could be used as a marker of epididymal maturation.