1. The testis of the ram secretes considerable amounts of amino acids (200μmoles/day) into the fluid collected from the efferent ducts. The principal amino acid in this testicular fluid is glutamate, which is present in concentrations about eight times those in testicular lymph or in blood from the internal spermatic vein. 2. The concentration of glutamate in seminal plasma from the tail of the epididymis is about ten times that in testicular fluid, and, though glutamate is the major amino acid in ejaculated seminal plasma, its concentration is less than in epididymal plasma. 3. After the intravenous infusion of [U−14C]glucose, labelled glutamate was found in the testicular fluid. Radioactivity was also detected in alanine, glycine, serine plus glutamine and aspartate. Alanine had the highest specific activity, about 50% of the specific activity of blood glucose. 4. When [U−14C]glutamate was infused, the specific activity of glutamate in testicular fluid was only about 2% that in the blood plasma. 5. Testicular and ejaculated ram spermatozoa oxidized both [U−14C]glutamate and [U−14C]leucine to a small extent, but neither substrate altered the respiration from endogenous levels. 6. No radioactivity was detected in testicular spermatozoal protein after incubation with [U−14C]glutamate or [U−14C]leucine. Small amounts of radioactivity were detected in protein from ejaculated ram spermatozoa after incubation with [U−14C]glutamate. 7. The carbon of [U−14C]glucose was incorporated into amino acids by testicular spermatozoa; most of the radioactivity occurred in glutamate.
