Effect of Ecdysone on Incorporation of C 14 -Leucine into Hepatic Protein in vitro. ∗

Previous studies(1) indicated that ecdysone, the growth and metamorphosis hormone of insects, may have an effect on mammalian cells also, even though no material yielding a positive bioassay was obtained from human tissues when methods of extraction yielding positive results in insects were used(2). Growth of mammalian cells in tissue culture was inhibited by the hormone(3,4), and a few regressions of sarcoma 180 occurred after injection of ecdysone. In a continuation of these studies, active hormone was added to the fraction of mammalian (murine) liver obtained from centrifugation of homogenates at 14000 × g, and results were compared to samples without the hormone. DL-leucine labeled in position one with C¹⁴ was added, and amount of incorporation into protein from zero time for a period of 30 minutes was determined by plating the insoluble material precipitated by trichloracetic acid and counting in the proportional range(5,6,7). (Removal of sources of energy from the system resulted in failure of synthesis to occur in both control and experimental groups, eliminating the possibility that they were supplemented by the hormonal extract.)

As much as a 10-fold increase in incorporation of leucine occurred when ecdysone was present in the preparation (Table I). The level of incorporation was increased significantly (t test) when ecdysone was present in concentrations of 250 c.u. or more per ml and the activity of leucine in each experiment adjusted to 10 millicuries per millimole. The effect was more pronounced with higher doses, and a threshold was present above a concentration of 100 c.u. per ml.

Although animals were fasted and conditions of study maintained as nearly constant as possible, results of determinations of uptake vary from one preparation to another. However, when the values for control and experimental values for paired samples from a single preparation are compared, those containing ecdysone (<100 c.u.) have a higher uptake in every case.