Thyroid hormone and hepatic UDP-glucuronosyl transferase activity: contrary effects in rat and mouse

The administration of tri-iodothyronine (T3) to female Sprague-Dawley (SD) rats lowered the basal activity of uridine diphosphoglucuronate glucuronosyl transferase (UDPGT:EC 2.4.1.17) for bilirubin (Bili) by 75 percent, but dramatically increased the level of UDP-glucuronosyl transferase for p-nitrophenol (UDPGT-PNP) by more than 100 percent. Similar experiments performed in four strains of female mice produced results contrary to those observed in the rat. T3 administered to C57BL/6J, DBA/2J, Swiss-Webster (SW) and CD-1 mice significantly increased hepatic UDPGT-Bili by 28, 69, 79 and 94%, respectively. The increase of UDPGT-Bili in the selected strains was observed to be inversely and linearly proportional to the basal level of enzyme measured in each strain (r = -0.99215; p less than 0.001). Only in the DBA/2J strain was UDPGT-PNP significantly diminished to 66% of control levels, producing a result exactly opposite to that observed in the SD rat; in the other three strains, UDPGT-PNP was not significantly altered.