Creatine synthesis and transport systems in the male rat reproductive tract

Previous studies from this laboratory showed that high levels of guanidinoacetate methyltransferase are present in mouse testis and epididymis, whereas guanidinoacetate methyltransferase mRNA and protein are not detected in seminal vesicles where large amounts of creatine (Cr) and phosphocreatine are found (Lee et al., Biol Reprod 1994; 50:152-162). To further investigate the origin(s) of Cr in the male reproductive tract, the expression patterns of the three enzymes and a transporter involved in Cr metabolism were examined with rat reproductive tissues. Western blot analysis showed that expression of L-arginine:glycine amidinotransferase was limited to the kidney. On the other hand, high levels of the mRNAs for both guanidinoacetate methyltransferase and Sadenosylhomocysteine hydrolase were expressed in the testis and epididymis as well as the liver and kidney. Cr transporter mRNA was highly expressed in the seminal vesicle and vas deferens. These results suggest that the source of Cr in the male reproductive tract varies depending on the tissue; in the testes and epididymides, Cr is synthesized from guanidinoacetate, while in the seminal vesicles, Cr is transported from blood. Previous and present findings suggest the importance of Cr metabolism and/or transport for reproductive functions.