Hepatic regeneration is associated with preservation of microsomal glucuronidation

Significant controversy exists regarding the regulation of glucuronidation during the process of hepatic regeneration. We used a partial hepatectomy rat model to elucidate the effects of hepatic regeneration on the various components of the microsomal glucuronidation system. Hepatic microsomes were prepared by standard sucrose density centrifugation, coupled with a modified technique involving Percoll centrifugation. Microsomal uridine diphosphate (UDP)-glucuronosyltransferase (UGT) protein expression and UGT messenger RNA (mRNA) levels were measured by Western and Northern blotting. UGT enzyme activity was determined toward two prototypical aglycones, p-nitrophenol and estrone, in intact and digitonin-treated microsomes. Microsomal uptake of the cosubstrate for all glucuronidation reactions, UDP-glucuronic acid (UDP-GlcUA), was determined using a rapid- filtration assay. Microsomal enrichment after hepatectomy was preserved only when the Percoll method was used. Microsomal UGT protein expression and UGT mRNA levels were unaltered after hepatectomy. UGT enzyme activity toward estrone was unchanged 1 day posthepatectomy compared with sham laparotomy controls. Similarly, p-nitrophenol glucuronide formation was unaffected by hepatic regeneration 1, 2, and 5 days posthepatectomy when digitonin-treated microsomes were used. Glucuronidation of p-nitrophenol in intact microsomes was increased in partial hepatectomy compared with sham-operated controls at 1 and 2 days. This increase was not attributable to changes in microsomal UDP-GlcUA uptake, which was comparable in both groups. We conclude that microsomal glucuronidation, in contrast to other well characterized hepatic metabolic functions, is highly preserved during liver regeneration.