Variations in catechol-O-methyltransferase activity in inbred strains of rats

Catechol-O-methyltransferase (COMT) activity was measured in nine strains of rats aged 9 to 11 weeks. Hepatic COMT activity levels in Sprague-Dawley and Fischer 344 animals varied from 48% to 66% of those in livers of the other strains studied. Kidney COMT levels in these same two strains were only 50% and 60%, respectively, of those in Wistar-Furth animals. There was no difference in the recovery of purified rat liver COMT added to homogenates of liver and kidney from Fischer 344 and Wistar-Furth animals, a finding that makes it less likely that the different levels of COMT activity were due to differences in levels of endogenous enzyme activators or inhibitors. Enzyme activity in heart, brain, and blood differed much less among the nine strains of rat than did hepatic COMT activity. Hepatic COMT activity levels in Sprague-Dawley and Fischer 344 animals were already significantly less than those in other strains at 2 weeks of age (p < .05). However, the magnitudes of the differences (73-86%) were smaller than were those present in more mature animals. The existence of striking differences of COMT activity among strains of rats may make possible genetic, biochemical and pharmacogenetic studies of strain differences of COMT in this species.