Pyrrolizidine alkaloid content of houndstongue (Cynoglossum officinale L.)

Houndstongue (Cynoglossum officinale L.) is a biennial weed infesting pasture, hayfields, and disturbed areas throughout North America. Houndstongue contains pyrrolizidine alkaloids (PAs) that are hepatotoxic. First and second year's growth of houndstongue were harvested from emergence to maturity. Nuclear magnetic resonance was used to determine the levels of total PAs, free base, and N-oxide forms of the alkaloids in leaves, stems, buds, flowers, and pods. PA levels generally were highest (1.5 to 2.0% dry weight) in immature plant tissue, with a gradual decline during maturation. Most plant parts contained greater quantities of the N-oxide form of PAs (60-90%) compared to the free base form. Leaves and pods of mature houndstongue contained sufficient PAs to be potentially toxic if ingested by livestock.