CHANGE IN Δ4-STEROID HYDROGENASE ACTIVITY IN RAT LIVER AFTER TUMOR IMPLANTATION

Abstract

For the purpose of clarifying the mechanism of altered metabolism of steroid hormones in tumor bearing animals, Δ4-steroid hydrogenase activity in Wistar strain rat liver was examined periodically after Rhodamine sarcoma implantation. The enzyme activity was determined according to Tomkins’ method using cortisol, cortisone and corticosterone as substrates. After tumor implantation, Δ4-steroid hydrogenase activity increased for a week, then began to decrease gradually as the tumor grew, and the low level of the activity was maintained until the sixth week, when the implanted tumors were totally extirpated. After the extirpation, Δ4-steroid hydrogenase activity in the liver of the surviving rats was measured for two weeks further. During this period the enzyme activity returned rapidly to its normal level. The decrease of the enzyme activity in tumor-bearing rat liver was confirmed also by the suppressed rate of metabolism of cortisol-4-14C in vitro in the Tomkins’ medium. Throughout the experiments the existence of Δ4-steroid hyclrogenase-suppressing factors in tumor-bearing rats was suggested.