Activation and inhibition of rat hepatic UDP-glucuronyltransferase by mercuric acetate

Abstract

1. The effects of mercuric acetate on glucuronide conjugation of bilirubin and 4-methylumbelliferone in vitro represent a new type of modifier of UDP-glucuronyltransferase activity.

2. Bilirubin UDPG-transferase was normally activated (optimally 4-fold), inhibition was seen only at high concn. of Hg^2-. 4-Methylumbelliferone UDPG-transferase was normally inhibited by Hg²⁺, but at high concn. of UDPGA (10mmol/l) slight activation was seen.

3. Activation of bilirubin conjugation was unaffected by Mg ²⁺ concn., indicating that the mechanism of Hg²⁺ activation differs from that caused by Mg²⁺.

4. Glucuronidation of bilirubin in liver microsomes from control rats, or rats treated with phenobarbital, methylcholanthrene or TCDD respond similarly to Hg²⁺, confirming the view that bilirubin conjugation is not inducible by these inducers.