Effects of dietary pyrrolizidine (Senecio) alkaloids on vitamin A metabolism in rats.

In two experiments, the effect of feeding the pyrrolizidine alkaloid (PA)-containing plant tansy ragwort (Senecio jacobaea) on the metabolism of vitamin A in rats was examined. In Experiment 1, dietary levels of 0, 5 and 10% tansy ragwort and 0, 25,000 and 100,000 IU supplementary vitamin A/kg diet were used. In rats fed tansy ragwort, both plasma and liver concentrations of vitamin A were depressed (P less than 0.05). Plasma values were decreased to about 50% of control values. In Experiment 2, rats fed 5% tansy ragwort had depressed plasma and liver vitamin A concentrations 48 h after oral dosing with vitamin A. Fecal excretion of vitamin A was decreased in tansy ragwort-fed rats. In control rats, most fecal vitamin A was excreted in the first 24 h post-dosing, while in tansy ragwort-fed animals, the excretion was delayed, suggesting a possible effect of PA on gut motility. The results indicate that PA causes reductions in liver and plasma vitamin A concentrations. Postulated mechanisms include an effect of PA on hepatic retinol-binding protein synthesis, and impaired biliary excretion depressing vitamin A absorption.