Effect of the Plant Product Croton Oil on the in vivo Incorporation of ³ H-Thymidine. Evidence for a Pronounced Inhibition in the Thymus

Abstract

An in vivo technique for screening interference with the DNA synthesis was used for evaluating the effects of croton oil (the oil from the seeds of Croton tiglium). The effect on the DNA turnover in various organs of the mouse was studied by measuring the incorporation of [6-³ H]-thymidine. Twenty-four hours after an intraperitoneal injection, croton oil (2 mg/kg) significantly reduced the uptake of ³ H-thymidine into the thymus, spleen, liver, and small intestine. The most potent effect was observed in the thymus, the incorporated amount of ³ H-thymidine corresponding to 11% of that found in the controls. The inhibitory effects of croton oil were transitory and no longer present three days after the injection. Croton oil is usually regarded as a tumour promoter, not being carcinogenic per se. It is therefore of interest to note that the active principle of croton oil (12-O-tetradecanoyl-phorbol-13-acetate, TPA) has been reported to induce skin tumours in mice. If this effect of TPA can be confirmed, it will support the idea that the present observation of a marked inhibition of the ³ H-thymidine incorporation may reflect genotoxic properties of croton oil.