Effect of pyrrolizidine alkaloids from tansy ragwort ( Senecio jacobaea) on hepatic drug-metabolizing enzymes in male rats

Abstract

Ad lib. consumption of diets containing 5% tansy ragwort ( Senecio jacobaea) for 1–4 weeks produced a 5- to 6-fold increase in hepatic microsomal epoxide hydrase and significant increases in cytosolic glutathione S-transferase activities in male Long-Evans rats. An enhancement of these enzyme activities was also observed when a diet containing 1% tansy ragwort was fed for a period of 3 weeks. Feeding a diet containing 0.5% pyrrolizidine alkaloid (PA) mixture extracted from tansy ragwort for 1 week produced a 5-fold increase in hepatic epoxide hydrase and a 73 per cent increase in glutathione S-transferase activities. In contrast, hepatic microsomal aryl hydrocarbon hydroxylase activity (AHH) was reduced significantly by feeding diets containing 5% tansy ragwort or a 0.5% alkaloid mixture. Hepatic microsomal cytochrome P-450 content was lowered following consumption of the 0.5% alkaloid mixture but not by feeding a 5% tansy ragwort diet, the difference presumably being a result of the lowered PA intake by the latter animals. Exposure to the pyrrolizidine alkaloids, therefore, may influence significantly the capacity of animals to metabolize endogenous or foreign compounds and possibly also affect the subsequent biotransformation and toxicity of these plant constituents.