Abolition of the apparent deficiency of 2-aminophenol glucuronidation in perfused Gunn rat liver by pentan-3-one

Effects of administration of N-nitrosodialkylamines and N-nitrodiethylamine on hepatic UDP-glucuronosyltransferase activity in Wistar rats

N-Nitrosodiethylamine (NEN) and N-nitrodiethylamine (NEA) are carcinogens and in vitro activators of hepatic UDP-glucuronosyltransferase (GT) toward 2-aminophenol (AP) and 4-nitrophenol (NP). In this communication, they were intraperitoneally administered to male Wistar rats for 7 days and GT activities were determined towards AP, NP, phenolphthalein (PH) and testosterone (TS). Administration of 30 or 20 mg/kg dose of NEN caused marked decrease of liver and body weights, and did not affect hepatic GT activities. Injection of 10 mg/kg dose of NEN did not diminish liver and body weights, and increased the maximally activated GT activities toward AP and NP. In contrast, 30 mg/kg dose of NEA, did not affect either liver and body weights or GT activities. N-Nitrosodimethylamine (NMN), which is a carcinogen and a weak in vitro AP GT activator, was more toxic than NEN, and 3.6 mg/kg dose of NMN appears to induce GT toward NP and AP. Administration of 46.5 mg/kg N-nitrosodibutylamine (NBN), which is a carcinogen but not a GT activator, did not affect GT activities or liver body weights.

Reconstitution of purified Wistar rat liver bilirubin UDP-glucuronyltransferase into Gunn-rat liver microsomes

1. Reconstitution of purified bilirubin UDP-glucuronyltransferase from Wistar-rat liver into Gunn-rat liver microsomes provides a better environment than phosphatidylcholine liposomes, such that the final specific activity of the Wistar-rat liver enzyme was increased up to 85 units/mg of protein. 2. Gunn- and Wistar-rat liver microsomes were equally effective for reconstitution of the purified enzyme. 3. The transferase activity does not appear to be fully expressed in the more rigid environment of foetal Wistar-rat liver microsomes. 4. These reconstitution experiments reveal a final specific activity for the purified bilirubin UDP-glucuronyltransferase consistent with the capacity of the whole rat liver to glucuronidate bilirubin and indicate that the absence of this enzyme activity in Gunn-rat liver microsomes is not due to an abnormal microenvironment.

Liver snips. A simple, rapid and reproducible method for studying metabolism in small fragments of tissue, as applied to glucuronidation in rat liver

A simple, rapid method is described of preparing intact cells as small (about 2mm) pieces of organized tissue capable of performing synthetic metabolic functions. It has been applied to the study of glucuronidation in rat liver. In this process, snips appear less damaged, more versatile and more active than tissue slices and yield results of reproducibility comparable with those with homogenates. From a comparison with the literature, snips glucuronidate the substrates employed at a rate much the same as in perfused preparations and some 30% less than the rate in isolated-hepatocyte suspensions; the advantages they offer in certain situations over these two techniques are discussed.