Cardenolides metabolism

Milek, R, Reinhard, E. and Kreis, W. (1997) Influence of precursors and inhibitors of the sterol pathway on sterol and cardenolide metabolism in Digitalis lanata Ehrh. Plant Physiol. Biochem., 35,111-21. 

Cardenolldes appear to be metabolized by a variety of species, possibly as a mechanism for converting these steroids into compounds that can be efficiently sequestered. The milkweed bug, Oncopeltus fasclatus, metabolizes (hydroxylates ) the nonpolar cardenollde dlgltoxln to more polar compounds that are subsequently sequestered In the dorsolateral space fluid (17. 18). Larvae of another cardenolide-adapted Insect, the monarch butterfly, Danaus plexlppus. also convert these steroids Into compounds that are readily sequestered. For example, uscharldln, which contains a carbonyl group at C-3 ( ) of the... 

Cardenolides vary in their absorption, distribution, metabolism, and excretion, as shown by comparison of three representative agents digoxin, digitoxin, and ouabain (Table 13-2). Of these three, digoxin is the only preparation used in the USA. 

Marty, M.A. and Krieger, R.I., Metabolism of uscharidin, a milkweed cardenolide, by tissue homogenates of monarch butterfly larvae, Danaus plexippus L. /. Chem. Ecol., 10,945,1984. 

Other enz)mies involved in pregnane metabolism will be introduced when discussing cardenolide and BR bios)mthesis (see Sections 6.3 and 6.4). 

Luckner, M. and Diettrich, B. (1985) Formation of cardenolides in cell and organ cultures of Digitalis lamta, in Primary and Secondary Metabolism of Plant Cell Cultures (eds K. Neumann, W. Barz and E. Reinhard). Springer-Verlag, Berlin, Heidelberg, New York, pp. 154-63. 

Various aspects of steroid biosynthesis were included in a Royal Society Symposium. The published proceedings and other reviews have dealt with cyclase enzymes,water-soluble steroids and triterpenoids, the involvement of a 14(15)- or 8(14)-double bond and its reductionin cholesterol biosynthesis, biosynthesis of sterols, steroid metabolism in insects, pregnane steroids, cardenolides, and bufadienolides. ... 

There are several research observations which support the utilization of cardenolides in milkweed by monarch butterflies for purposes of defense. First, the monarch larvae feed exclusively on species of Asclepias through all developmental stages (Urquhart, 1960). Second, the insects are capable of selective storage of some cardenolides among different members of Asclepiadaceae (Roeske et al., 1976 Brower et al., 1982). Finally, metabolic conversion to specific types of cardenolides occurs in the monarch (Seiber et al., 1980). These data and the emetic response ellicited by the cardenolides in vertebrates provide compelling evidence on behalf of the utilization of phytochemicals by insects for the purpose of defense against predators. 

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