PRINCIPLES OF TOXICOLOGY

17.6 TOXINS OF HIGHER PLANTS 421
TABLE 17.3 Some Common Flowering Plants, their Alkaloid or Peptide Toxins, and Major Symptoms
Associated with their Ingestion
Toxin Type of Compound Plant (Toxic Parts) Symptoms
Solanine Saponin Potato (Spuds, Stressed tuber) Headache, fever, abdominal pain,
hemorrhagic vomiting, diarrhea
Oleandrin Cardiac glycoside Oleander (all parts) Headache, nausea, vomiting,
diarrhea, bradycardia, irregular
pulse, coma, respiratory
depression
Grayanotoxin Diterpene Rhododendron, Azalea (all parts) Salivation, vomiting, hypotension,
convulsions, weakness
Coniine Piperidine Poison hemlock (all parts) Tremor, motor weakness,
vomiting, diarrhea, dilated
pupils, bradycardia, coma
Lupinine Quinolizidine Lupine (all parts, esp. seeds) Vomiting, salivation, nausea,
dizziness, headache, abdominal
pain
Cicutoxin Complex alcohol Water hemlock (all parts, esp. Tremors, dilated pupils,
roots)
convulsions, respiratory
depression
Ricin Peptide Castor bean (chewed seed) Pain in mouth; delayed onset:
abdominal pain, vomiting,
severe diarrhea, hemolysis,
renal failure
Viscotoxin Peptide Mistletoe (all parts, esp. berries) Vomiting, diarrhea, hypotension,
bradycardia
in traditional herbal medicine, their clinical efficacy in the treatment of most of these disorders has not
yet been demonstrated.
Alkaloid Toxins Thousands of compounds of this type have been isolated and investigated, in many
cases quite superficially. Most of these substances can also be called heterocyclic compounds, as they
generally possess a ring structure containing at least one non-carbon atom, usually N or O. Flowering
plants have been a particularly rich source of alkaloids, and apart from the antimicrobial drugs, which
are mostly derived from bacteria, most drugs have originated directly or indirectly from alkaloids found
in the flowering plants. Some flowering plant alkaloid toxins are listed in Table 17.3.
One of the most commonly used alkaloids is nicotine, the substance that stimulates “nicotinic”
cholinergic receptors. In addition to its self-administration as tobacco, nicotine and related compounds
are useful toxins for controlling certain insect pests. Because the free base form of nicotine rapidly
diffuses across the skin, this substance can be quite toxic to farm workers applying it as an insecticide
or to laboratory scientists who are handling the free base. Another heterocyclic compound, reputedly
taken by the Greek philosopher Socrates, is coniine, a major alkaloid in poison hemlock potion. Two
thousand years later, the mechanism of action of this infamous toxin is still unknown! A South
American arrow poison alkaloid, tubocurarine, acts as a competitive antagonist of ACh and nicotine
at the skeletal muscle neuromuscular junction.
In recent years a significant number of alkaloids were also isolated from less traditional sources
such as marine organisms, and some of these are also toxins.
Flowering Plants Containing Peptide and Protein Toxins Several plants contain protein toxins that
are lethal when orally ingested or parenterally administered. Rosary bean seeds are quite attractive red
seeds with a black spot, and as the name indicates, are often used to make necklaces. These seeds
contain a 70-kD protein called abrin, which is a ribosomal protein synthesis inhibitor. The castor bean,