Biol. Pharm. Bull. 29(2) 202—205 (2006)

enzyme which inactivates the released catecholamines from nerve endings by methylating their catechol moieties using S-adenosyl-L-methionine (SAMe) as a methyl donor. COMT is found in most mammalian tissues, with highest activity in the liver and the kidney. There are two COMT isoforms: in the cytoplasm as soluble COMT (S-COMT) and in association with membranes as membrane-bound COMT (MB-COMT). S-COMT protein is more prevalent than MBCOMT in all tissues in rats. Catecholamines, norepinephrine (NE), dopamine and epinephrine, play important roles in the central nervous system as in the periphery, and in central regions, catecholaminesrelated gene expression was correlated with blood pressure. We have previously reported an assay method for rat brain COMT activities, using NE as an endogenous substrate. The use of the endogenous substrate provides significant information of COMT in vivo as compared with formerly reported method which uses an artificial substrate, 3,4-dihydroxybenzoic acid (DBA). Endogenous NE has higher affinity for COMT than DBA, and our method is more sensitive to measure COMT activity. In this study, COMT activities were evaluated in cerebral cortex, cerebellum, hippocampus, brain stem, hypophysis, and hypothalamus in order to evaluate the role of COMT in blood pressure regulation using spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. In addition, in order to investigate the contribution of COMT activities to NE metabolism, NE and its 3-Omethyl metabolite, normetanephrine (NMN), concentrations were examined in discrete areas of SHR and WKY rats.