Carnitine Transport into the Perfused Epididymis of the Rat: Regional Differences, Stereospecificity, Stimulation by Choline, and the Effect of Other Luminal Factors1

Abstract

The transfer of carnitine from blood into the perfused, sperm-free lumen of segments of the epididymis has been examined in anesthetized rats. During i.v. infusion of DL-[³ H]-carnitine, radioactive material with chromatographic properties similar to those of free carnitine appeared in perfusates flowing at 1.0-l.3 µl/min through the distal cauda epididymidis within 30 min and slowly attained plateau values at 2-4 h. The entry rate showed a significant (P3 H]-carnitine into the lumen of the corpus epididymidis and the secretion of carnitine into the perfusate from ∼200 to 350 pmol/h/cm. In dual isotope infusions of the enantiomers of carnitine, the transport of L-carnitine into the distal cauda epididymidis exceeded that of the D-form 14-fold, and choline (20m mM) in the perfusing solution stimulated the entry of both, but to different extents. A model for the transport of carnitine across the epithelium of the epididymis is proposed.