The endogenous nitric oxide (NO) synthase (NOS) inhibitor asymmetrical dimethylarginine (ADMA) is elevated in many patients and may contribute to the initiation and progression of their disease. While some mechanistic pathways have been identified, tissue-specific contributions to ADMA control remain unclear. We sought to determine if whole blood (WB) could participate in ADMA control ex vivo. Anesthetized male Sprague-Dawley rats underwent exsanguinations, and WB preparations were incubated at 37°C for 5 h. ADMA and symmetrical dimethylarginine were analyzed by high-pressure liquid chromatography. Incubation of lysed red blood cell (RBC) supernatant yielded a significant decrease in ADMA that was blocked by 4124W, a synthetic inhibitor of dimethylarginine dimethylaminohydrolase, the only reported enzyme to hydrolyze ADMA. Hydrolysis of ADMA was diminished by addition of physiologically relevant concentrations of zinc (i.e., 20 M). Conversely, when rat WB or WB supernatant was incubated at 37°C, it liberated quantities of free ADMA (1-2 M) that in vivo would likely have pathological consequences. Addition of arginine methyltransferase inhibitors to these incubations did not reduce ADMA release, indicating no dominant role for active protein methylation during these incubations. This ADMA liberation was significantly reduced by addition of protease inhibitors, indicating a dependence on peptide bond hydrolysis. Total ADMA (protein incorporated plus free) was determined by acid hydrolysis and found to be 43.18 Ϯ 4.79 M in WB with ϳ95% of this in RBCs.These ex vivo data demonstrate the potential of blood to control the NO-NOS system by modulating free ADMA. nitric oxide; protein arginine methyltransferase; symmetrical dimethylarginine; protease NITRIC OXIDE (NO) is produced by NO synthase (NOS) and has a myriad of functions throughout the body, including vasodilation, signaling functions, and inhibition of platelet aggregation. Deficiency or loss of NOS activity has been termed "endothelial dysfunction" and may contribute to a spectrum of cardiovascular diseases. Asymmetrical dimethylarginine (ADMA) and N G -monomethyl-L-arginine (L-NMMA) are endogenous inhibitors of NOS, but the concentration of ADMA exceeds that of L-NMMA by ϳ10-fold (60) and hence is of greater potential clinical interest. ADMA and its noninhibitory regioisomer, symmetrical dimethylarginine (SDMA) (6, 12), are released into the plasma following the breakdown of proteins containing arginine residues previously dimethylated by protein arginine methyltransferases (PRMT) (37). The literature contains compelling evidence that elevated plasma ADMA exists in diabetes mellitus (37), hypertension (1, 15, 22, 45, 51, 52), hypercholesterolemia (6), hyperhomocyst(e)inemia (50), experimental hemorrhage (4), preeclampsia (16), and sickle cell anemia (47). ADMA has also been reported to increase platelet activation and atherogenesis in the cardiovascular system (33). Cooke (11, 13) and others (17,59) give extensive reviews of much of these data and argue that ...

No abstract