The Physiological Effects and Toxicokinetics of Tall Larkspur (Delphinium barbeyi) Alkaloids in Cattle

摘要

Toxic larkspur (Delphinium) species have been responsible for large losses to the cattle industry in western North America since the beginning of the 20th century (Marsh et al. 1916; Pfister et al. 1999, 2003). The initial symptoms of larkspur poisoning in cattle include lack of appetite, general uneasiness, nausea, rapid pulse and respiration, and a stiff staggering gait (Marsh et al. 1934; Nation et al. 1982). As the poisoning proceeds bloating, respiratory depression, tremors in locomotor musclesleading to more generalized tremors, failure of voluntary muscular coordination, and finally collapse to sternal or lateral recumbency occur (Olsen et al. 1990). The poisoning of cattle from the consumption of larkspur has been attributed to diterpenoidalkaloids produced by the plant and found in high concentration in plant tissues. Total diterpenoid alkaloid content can represent 3% of plant dry weight and is a mixture of 10-15 alkaloids belonging to three structural classes-the norditerpenoid alkaloids; C2o-diterpenoid alkaloids; and ^^-diterpenoid alkaloids-that vary in relative abundance between species of larkspur (Olsen et al. 1990). The norditerpenoids are the most toxic and can be further subdivided into two main structural groups, the ^-(methylsuccinimido) anthranoyllycoctonine type (MSAL-type) and 7,8-methylenedioxylycoconine type (MDL-type) norditerpenoid alkaloids of which the MSAL-type alkaloids are the most toxic (Olsen et al. 1990; Manners et al. 1993, 1995). The most abundant membersof the MSAL-type alkaloids group include methyllycaconitine (MLA), nudicauline, and 14-deacetylnudicauline (Gardner et al. 1997). Plants high in MSAL-type alkaloids are thought to be the most toxic to cattle and the concentrations of these alkaloids havebeen used for the prediction of plant toxicity (Pfister et al. 2002; Ralphs et al. 2002).