Comparison of the acute toxicity of zygacine versus zygadenine.

Foothill death camas (Zigadenus paniculatus) is a common poisonous plant found throughout western North America. The toxic alkaloids in foothill death camas are zygadenine, esters of zygadenine, with zygacine, the 3-acetyl ester of zygadenine, often being the most abundant. Two additional esters of zygadenine that are found primarily in the floral parts of foothill death camas are 3-angeloylzygadenine and 3-veratroylzygadeine. Recent research has shown that very little zygacine is detected in the blood of animals dosed with zygacine. A recent investigation into the metabolism of zygacine demonstrated that zygacine is rapidly metabolized to zygadenine, demonstrating a clear first pass effect. The objective of this study was to determine if there is a difference in the acute toxicity of zygacine and zygadenine to mice and sheep. Additionally, two other esters of zygadenine, 3-angeloylzygadenine and 3-veratroylzygadenine, were evaluated for their acute toxicity in a mouse IV LD assay. All three esters of zygadenine tested were more toxic than zygadenine, with the following rank order of toxicity in the mouse IV LD assay: zygadenine-HCl (59.5 mg/kg) < zygacine-HCl (1.6 mg/kg) < angeloylzygadenine-HCl (1.0 mg/kg) < veratroylzygadenine-HCl (0.5 mg/kg). Similar to the results of the mouse experiments, zygacine-HCl was significantly more toxic than zygadenine-HCl in sheep dosed IV with pure compounds. Sheep dosed with 1.25 mg/kg zygacine-HCl showed severe clinical signs of poisoning. Whereas a dose of 12.5 mg/kg zygadenine-HCl was required to elicit a similar onset and severity of clinical signs. Overall, these data indicate that zygacine is more toxic than zygadenine when administered IV, when first pass metabolism is bypassed.