The structures and nomenclature of the chemical constituents of Panax ginseng have been discussed elsewhere (78) (see also Section 9).
P-Sitosterol is a steroid sapogenin that has been isolated from ginseng. Approximately 50-60% of a dose of P -sitosterol is absorbed from the gastrointestinal tract in rats (79). After oral administration of radiolabeled ginsenoside Rg1, blood radioactivity peaked at 2.1 hours. Bioavailability was 49% (80).
Studies of the distribution of [3H]ginsenoside Rg1 following intravenous injection have been performed in mice (80). Tissue radioactivity was greatest in the kidney, followed by the adrenal gland, liver, lungs, spleen, pancreas, heart, testes, and brain. Plasma protein binding was 24%, and tissue protein binding was 48% in the liver, 22% in testes, and 8% in the brain.
The blood radioactivity decreased in a triphasic manner after intravenous injection of [3H]ginsenoside Rg1 to mice (80). Other Chinese studies have characterized the biotransformation of ginsenoside 20(S)-Rg2, one of the main constituents of ginseng roots and leaves. Its metabolism is complex and involves multiple hydrolysis reactions in the gastrointestinal tract. Metabolites of 20(S)-Rg2 include 20(S)-Rh1 and 20(S)-protopanaxatriol. Details of the biotransformation of 20(S)-Rg2 and chemical structures of the ginsenosides are available in the cited reference (80).
Corroborating two rat studies (81,82) suggesting that only trace amounts of ginsenosides are excreted in the urine, low levels of ginsenoside aglycones were identified using gas chromatography-mass spectroscopy to analyze urine samples of 65 athletes claiming to have ingested ginseng within the 10 days prior to urine collection (14). An aglycone (molecule from which the sugar moiety has been removed) of ginsenosides, 20(S)-protopanaxatriol, was found at concentrations between 2 and 35 ng/mL in approx 90% of the urine samples studied. Another aglycone, 20(S)-protopanaxadiol, was barely detectable despite the fact that the ginsenosides from which it is derived were the major ginsenosides found in the commercially available Swedish ginseng products analyzed by the investigators.
This indicates that these two ginsenosides have different pharmacoki-netics. Because the actual amount of ginseng ingested and the time since ingestion were unknown, little else can be inferred from these data.
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