Metabolism of Estrogens in Hepatomas of Different Growth Rates

The activity of estrogen 16a-hydroxylase was measured for nine Morris hepatomas of different growth rates and host livers. Activity was measured in the microsomal fraction of the cell (100,000 x g). In the spectrum of hepatomas studied, 16a-hydroxylase activity was significantly decreased in parallel with the increase in hepatoma growth rate. The decrease in enzymic activity ranged from 16 to 19% for the slow-growing tumors (Hepatomas 44, 28A, and 9633), 2 to 9% for the intermediate-growing tumors (Hepatomas 38B, 7795, and 5123A), and 0% for the fast-growing tumors (Hepatomas 7288C, 7777, and 42A). Estrogen 16a-hydroxylase activity of the liver of tumor-bearing rats differed from that of liver of healthy animals. There was a decrease in enzymic activity ranging from 66% to 90% of normal control rats. The activity level of the host liver did not correlate with tumor growth rate. Stimulation of 16a-hydroxylase with phenobarbital showed a 4-fold increase in activity in normal liver and only a 2-to 3-fold increase in host livers. The slow-and intermediate-growing hepatomas showed a 1.2-to 1.4-fold increase in enzyme activity, and no activity or stimulation in the fast-growing hepatomas was observed.