Morphine regulation of a novel uridine diphosphate glucuronosyl-transferase in guinea pig pups following in utero exposure

The uridine diphosphate glucuronosyltransferases (UGTs) catalyze conjugatio n reactions between various substrates and glucuronic acid, UDPGA (uridine diphosphate glucuronic acid), within the endoplasmic reticulum. Conjugation with UDPGA (glucuronidation) is an important pathway in the elimination, d etoxification, and activation of compounds including steroid hormones, xeno biotics, and quaternary ammonium substrates. The guinea pig, which has a pl acental structure and a glucuronidation profile for morphine that are simil ar to the human, serves as a good small animal model to study the ontogeny of UGTs and the effect of in utero exposure to morphine on UGTs. We examine d type 2 UGTs expressed in the guinea pig using amplification and cloning o f partial cDNAs from liver RNA. Sequence analysis revealed a novel UGT2 (su bsequently named UGT2A3),(2) that has a 64% amino acid sequence similarity to a known UGT2.(3) Full-length cDNAs were isolated from a guinea pig liver cDNA library. Tissue distribution of UGT2A3 using Northern blot analysis s howed expression of three distinct size UGT2A3 mRNAs with unique expression in liver and small intestine. UGT2A3 mRNA is expressed at high levels in l iver and lower levels in kidney and small intestine. In utero exposure to c hronic intermittent morphine resulted in the up regulation of mRNA in 7-day -old female pups' liver and kidney as determined by quantitative RT-PCR ana lysis. The conjugation profile for UGT2A3 using stable expression in CHO ce lls and thin-layer chromatography demonstrated active conjugation of phenol ic substrates. Regulation of UGTs by in utero morphine exposure may play an important role in fetal development. (C) 1999 Academic Press.