Isoform-specific regulation by NG,NG-dimethylarginine dimethylaminohydrolase of rat serum asymmetric dimethylarginine and vascular endothelium-derived relaxing factor/NO

Abstract

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 2- and 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. © 2007 American Heart Association, Inc.