Creatine Synthesis in the Testis

When guanido-L-arginine-14C was injected directly into rat testis, both guanidoacetic acid and creatine were significantly labeled in the testis after 30 min. About 7% of the total dose of radioactivity injected was recovered in creatine while 8% of the dose was recovered in guanidoacetic acid. Similarly, guanidoacetic acid-2-14C injected into the testis was converted to labeled creatine; 3% of the total dose of radioactivity injected was found in creatine after 15 min. These data, along with the specific activity relationships observed among arginine, guanidoacetic acid, and creatine support the existence of the classical pathway for creatine biosynthesis in rat testis, namely, creatine.