Isoform-Specific Regulation by N,N-Dimethylarginine Dimethylaminohydrolase of Rat Serum Asymmetric Dimethylarginine and Vascular Endothelium-Derived Relaxing Factor/NO

Asymmetric dimethylarginine (ADMA), which inhibits NO synthase, is inactivated by N,N-dimethylarginine dimethylaminohydrolase (DDAH). We tested whether DDAH-1 or -2 regulates serum ADMA (SADMA) and/or endothelium-derived relaxing factor (EDRF)/NO. Small inhibitory (si)RNAs targeting DDAH-1 or -2, or an siRNA control were given intravenously to rats. After 72 hours, EDRF/NO was assessed from acetylcholine-induced, NO synthase–dependent relaxation and 4-amino-5-methylamino-2 ,7 -diflouroflourescein diacetate for NO activity in isolated mesenteric resistance vessels (MRVs). Expression of mRNA for DDAH-1 versus -2 was 2and 7-fold higher in the kidney cortex and liver, respectively, whereas expression of DDAH-2 versus -1 was 5-fold higher in MRVs. The proteins and mRNAs for DDAH-1 or -2 were reduced selectively by 35% to 85% in the kidney cortex, liver, and MRVs 72 hours following the corresponding siRNA. SADMA was increased only after siDDAH-1 (266 25 versus 342 39 [mean SD] nmol L ; P 0.005), whereas EDRF/NO responses and NO activity were not changed consistently by siDDAH-1 but were greatly reduced after siDDAH-2. Mean arterial pressure was not changed significantly by any siRNA. In conclusion, SADMA is regulated by DDAH-1, which is expressed at sites of ADMA metabolism in the kidney cortex and liver, whereas EDRF/NO is regulated primarily by DDAH-2, which is expressed strongly in blood vessels. This implies specific functions of DDAH isoforms. (Circ Res. 2007;101:627-635.)