Quantitative tissue and gene-specific differences and developmental changes in Nat1, Nat2, and Nat3 mRNA expression...

Human N-acetyltransferase 1 (NAT1) and 2 (NAT2) are important phase II enzymes involved in the biotransformation of xenobiotics. In toxicity and carcinogenicity studies, functional polymorphism of rat N-acetyltransferase is considered a model for similar human variability. To accurately quantitate expression of the three rat N-acetyltransferases, we developed sensitive, specific assays for Nat1, Nat2, and Nat3 mRNAs. In male F344 rats, tissue-specific expression varied over a limited range for both Nat1 (approximately 19-fold) and Nat2 (approximately 30-fold), with the highest expression of both genes in colon. Expression of Nat3 mRNA was at least 2 to 3 orders of magnitude less than that of Nat1 or Nat2. Comparison of Nat1 and Nat2 mRNA expression in bladder, colon, liver, and lung of male and female F344 rats detected no significant gender-specific difference. In Sprague-Dawley and F344 rats ranging in age from neonate to mature adult, colon showed a >10-fold increase in Nat2 during the first postnatal month that did not correlate with changes in Nat1. In contrast, Nat2 showed no developmental change in Sprague-Dawley or F344 liver as Nat1 increased modestly. These measures of rat Nat expression confirm that Nat3 expression is negligible and that Nat1 and Nat2 are the primary determinants of arylamine acetylation activity in all tissues tested. The findings demonstrate differential tissue-specific and developmental regulation of the rat Nat1 and Nat2 genes and contribute to more complete understanding of tissue-, gender-, and development-specific expression patterns of the cognate N-acetyltransferase genes of humans and other species.