The role of cardenolides in a crucifer-insect relationship.

The cardenolides belong to a group of steroidal compounds, which, along with the bufadienolides, are referred to as cardiac glycosides because of their cardiotonic properties. As a result of this bioactivity, they are widely used to treat congestive heart failure. The bufadienolides are characteristic of toads in the family Bufonidae, which secrete the compounds from specialized glands when they are threatened by predators. Cardenolides, however, are produced almost exclusively by plants and serve to protect these plants from herbivory.1 The protective qualities of cardiac glycosides stem from their extreme toxicity to most higher animals and insects, due to inhibition of Na+K+-ATPase and the resulting effects on the sodium pump. However, at low concentrations, they are valuable medicinal drugs for humans and they have also been shown to have cytotoxic activity against cancer cell lines.2