Submitted to: Biochemical Systematics and Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2001
Publication Date: March 1, 2002
Citation: PANTER, K.E., MANNERS, G.D., JAMES, L.F., GARDNER, D.R., RALPHS, M.H., PFISTER, J.A., STEGELMEIER, B.L., LEE, S.T. LARKSPUR POISONING: TOXICOLOGY AND ALKALOID STRUCTURE ACTIVITY RELATIONSHIPS. BIOCHEMICAL SYSTEMATICS AND ECOLOGY. 2002. Interpretive Summary: Larkspurs cause serious economic losses to cattle producers on mountain rangelands in the western U.S. Three types of larkspurs have been classified including: tall larkspurs growing on mountain ranges; plains or intermediate larkspurs growing on the plains of Wyoming, Colorado and Nebraska; and low larkspurs growing on the foothill and desert rangelands. Research at the Poisonous Plant Research Lab in Logan, UT. focuses on the identification of the toxic alkaloids, screening these alkaloids for toxicity, determining why poisoning occurs and developing methods to reduce cattle losses. Alkaloids have been characterized and assigned to one of three classes (high, moderate and low) based upon chemical structural aspects and relative toxicity. In this paper we review the toxicology of the larkspur alkaloids, their mode of action or how they cause poisoning and the chemical structural components that are important in causing toxicity.
Technical Abstract: Tall larkspurs (Delphinium spp.) continue to be the most serious cause of cattle losses on mountain rangelands in the western U.S. Over 40 norditerpenoid alkaloids have been reported in species of larkspurs and toxicology data on 25 of these have been reported by us. These alkaloids can be classified into three general types based on their structural characteristics and toxicity: The N-(methylsuccinyl) anthranoyl-lycoctonin (MSAL)-type, having high toxicity; the lycotonine-type, with moderate toxicity; and the 7,8-methylenedioxylycoctonine (MDL)-type, of low toxicity. The structural importance of the methylsuccinimido anthranilic acid ester group at the C18 position is evident in the high toxicity of MSAL alkaloids, particularly methyllycaconitine (MLA), Nudicauline (NUD) and 14-deacetylnudicauline (14-DAN). Other structural aspects of these alkaloids such as the C14 functionality are also important as demonstrated by the reduced toxicity of barbinine. Methyllycaconitine is the alkaloid of most importance in toxicity of larkspurs on mountain rangelands because of its prevalence in most larkspurs and high toxicity. While Nudicauline and 14-deacetylnudicauline also possess high toxicity, they are relatively minor components in few larkspur species (generally the plains and low larkspurs) but when present at concentrations > 1mg/g dry weight they contribute significantly to overall toxicity. Delta line is often found in high concentrations in many larkspurs but because of low toxicity, its contribution to larkspur poisoning in the field is relatively minor and it will probably not cause toxicosis in the absence of the MSAL-type alkaloids.