Accumulation of Carnitine by Bovine Spermatozoa during Maturation in the Epididymis

The free carnitine content of bovine epididymal spermatozoa taken from the distal caput, midpiece, and proximal and distal cauda was measured and the average values were 0.07, 0.28, 0.49, and 1.0 µmole/109 cells, respectively. Carnitine was not detected in testicular spermatozoa. Acetyl-carnitine was detected only in caudal sperm and amounted to 10 to 20% of the total HClO4-soluble carnitine. This amount was increased to 67% by incubation of caudal cells in fructose. Caput spermatozoa incubated in [methyl-14C]carnitine took up radioactivity but caudal cells did not. The rate of carnitine uptake was related to concentration, maximal rates (1.7 nmoles per hour per 109 cells) were observed in 1 mm l-carnitine. The rate was linear with time for 2 hours and with cell number from 1 x 108 to 2 x 109. The relationship between spermatozoal carnitine levels and epididymal function is discussed.