G. biloba produces vasodilating effects on both the arterial and venous circulation.60,61 The result is increased tissue perfusion (i.e., in the peripheral circulation) and cerebral blood flow. The extract produces arterial vasodilatation (rodent models), dampens arterial spasticity, and decreases capillary permeability, capillary fragility,60 erythrocyte aggregation, and blood viscosity. There are several possible explanations for these effects. One possibility is that the compounds in G. biloba extract inhibit prostaglandin and thromboxane biosynthesis. It has also been speculated that G. biloba extract has an indirect regulatory effect on catecholamines. Ginkgolide B is reportedly a potent inhibitor of PAF.15 In any case, the effects are caused by a mixture of the constituents, not a single one.
G. biloba has become popular because of its putative abilities to increase peripheral and cerebral circulation. The herb is called an adaptogen,63 a drug that helps persons handle stress. In the periphery, the herb has been compared to pentoxifylline. If the properties are true, the herb could be used for intermittent claudication. If cerebral blood flow can be increased with G. biloba, the herb might be useful for disorders of memory that occur with age and Alzheimer disease. The popular use for the herb is to help people think better under stress and to increase the length of time that someone (e.g., a student) can handle mental stress.
Ginseng is the root of the species Panax quinquefolius. This form is commonly known as American, or Western, ginseng. The shape of the root is important to many and may make it highly prized. Panax means "all" or "man." Sometimes, the root is shaped like the figure of a human. The doctrine of signatures would say that this root would benefit the whole person. Another species of ginseng, Panax ginseng, is commonly called Asian, or Korean, ginseng. Chemically, the two species are very similar. Major components are named the ginsenosides (Figs. 29.13, 29.14).64
The chemical constituents of ginseng are called ginseno-sides or panaxosides. A total of 12 of these have been isolated but are present in such small quantities that purification is difficult. Sterols, flavonoids, proteins, and vitamins (B1, B2, B12, pantothenic acid, niacin, and biotin) are also components with pharmacological activity. The chemistry of ginseng gives a good example of how different compounds in
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