Inhibition of Sperm Maturation Through Intervention of the Carnitine System

Carnitine, acetylcarnitine and carnitine acetyltransferase (E.C.2.2.1.7) are present in 6–120 fold higher concentrations in human spermatozoa than in seminal plasma. Carnitine uptake by epididymal tissue in vitro in the rat is most active in the same segments of epididymis where the highest concentrations of carnitine are found in man. Radiolabelled carnitine is not taken up by mature human spermatozoa. Carnitine suppresses oxygen uptake in bovine ejaculated spermatozoa but not in human ejaculated or in rat or bovine epididymal spermatozoa. These findings indicate that the epididymis contributes to the accumulation of carnitine in caput spermatozoa and that carnitine may not be primarily responsible for the quiescent state of the spermatozoa in the cauda epididymis. Extensive changes in carnitine uptake in the epididymis can be encouraged by a hormonal treatment which has no effect on the carnitine uptake by the heart. This raises the possibility of interference with the carnitine balance in the epididymis without effecting the pattern of carnitine uptake in other tissues.