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Plants and Society, 3/e
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Medicinal Plants

Chapter Summary

1. From the earliest civilizations, native plants have supplied medicinal compounds. Western medicine traces its traditions back to Greek and Roman herbal remedies that were used for hundreds of years. During the Renaissance, there was a renewal of interest in herbalism and a revival of the Doctrine of Signatures. Although herbalism waned in the eighteenth and nineteenth centuries, many of the remedies became incorporated into modern prescription drugs. Today, 25% of prescription drugs are of plant origin, and an even greater percentage is based on synthetic or semisynthetic ingredients originally isolated from plants. While Western medicine strayed away from herbalism, 75%–90% of the rural population in the rest of the world still relies on herbal medicine as their only health care. Today, there is renewed interest in studying the medicinal plants used by indigenous populations in remote areas of the world, especially the rain forests. Investigating these folk remedies may lead to important medical discoveries that could save millions of lives.

2. Alkaloids and glycosides have been identified as the therapeutically important components of most medicinal plants. Alkaloids are a diverse group of compounds that contain nitrogen, are alkaline, and have a bitter taste. Alkaloids have pronounced effects on the physiology of animals, especially affecting the nervous system. They are widely distributed among plants, with three families known to contain abundant alkaloids: the Fabaceae, Solanaceae, and Rubiaceae. Glycosides are another diverse group of compounds; the feature they share is the presence of a sugar molecule attached to the active component. The physiological effects depend on the nature of the active component such as the cardioactive glycosides, which affect the contractions of heart muscle.

3. Digitalis, aspirin, quinine, reserpine, vinblastine, and vincristine are just a few of the countless plant-based medicinal compounds that form the basis of modern medicine. Digitalis, the primary treatment for several heart ailments, is derived from foxglove, a biennial in the snapdragon family. The leaves contain more than 30 glycosides, with digoxin and digitoxin the most medically significant compounds.

4. Today, aspirin is purely synthetic, but it is based on traditional remedies from willow bark. Salicylic acid, the active principle in willow bark, was identified early in the nineteenth century, and laboratory synthesis was achieved about 30 years later. In 1898, the Bayer Company developed acetylsalicylic acid, a modification they named aspirin.

5. Quinine, the active alkaloid in the bark of Cinchona trees, has been used for centuries in the treatment of malaria. Although synthetic drugs are usually prescribed today, quinine is still an effective treatment and is the drug of choice for infections resistant to the synthetics.

6. In 1952, the alkaloid reserpine was isolated from the roots of Rauwolfia serpentina, a plant used by Hindu healers for thousands of years. Although first used as a tranquilizer, reserpine and other Rauwolfia alkaloids have their greatest use in the treatment of hypertension.

7. The sap of Aloe vera contains several glycosides that are used to treat minor burns and cuts. This herbal remedy, which has been used since ancient times, promotes healing and reduces scarring. The moisturizing effect of the sap has resulted in its inclusion in skin creams, shampoos, lotions, and other cosmetics.

8. Ephedrine and pseudoephedrine, alkaloids from various species of Ephedra, are found in prescription and over-the-counter decongestants. Ephedrine is also a potent stimulant, and abuse of this compound in herbal remedies has led to proposed restrictions by the U.S. Food and Drug Administration.

9. Active compounds from several plants have become standard treatment for various forms of cancer, and researchers continue to look for and develop new anticancer compounds. The alkaloids vinblastine and vincristine, isolated from the Madagascar periwinkle, are remarkably effective in the treatment of certain forms of leukemia. Taxol, from the bark of the Pacific yew, has proved useful in the treatment of ovarian and breast cancer.

10. Herbal remedies are becoming a major component of alternative medical treatments in the United States. These widely available dietary supplements often contain secondary compounds that can have powerful effects on the human body but are generally marketed without rigorous scientific studies. Although many herbal remedies show great promise, some of them may interact with prescription and over-the-counter drugs.