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Bulbus Allii Sativi
injection of a mixture of diallyl disulfide and diallyl trisulfide (66). The
mechanism of garlic’s antihypercholesterolaemic and antihyperlipidaemic
activity appears to involve the inhibition of hepatic hydroxymethylglutaryl-CoA
(HMG-CoA) reductase and remodelling of plasma lipoproteins
and cell membranes (67). At low concentrations (0.5 mg/ml) cholesterol biosynthesis was inhibited in
the later stages of the biosynthetic pathway (68). Alliin was not effective,
but allicin and ajoene both inhibited HMG-CoA reductase in vitro (IC 50
= 7 and 9 mmol/l respectively) (49). Because both allicin and ajoene are
converted to allyl mercaptan in the blood and never reach the liver to affect
cholesterol biosynthesis, this mechanism may not be applicable in
vivo. In addition to allicin and ajoene, allyl mercaptan (50 mmol/l) and
diallyl disulfide (5 mmol/l) enhanced palmitate-induced inhibition of
cholesterol biosynthesis in vitro (50). It should be noted that water extracts
of garlic probably do not contain any of these compounds; therefore
other constituents of garlic, such as nicotinic acid and adenosine,
which also inhibit HMG-CoA reductase activity and cholesterol biosynthesis,
may be involved (69, 70).
The antihypertensive activity of garlic has been demonstrated in vivo.
Oral or intragastric administration of minced garlic bulbs, or alcohol or
water extracts of the drug, lowered blood pressure in dogs, guinea-pigs,
rabbits, and rats (52, 71–73). The drug appeared to decrease vascular resistance
by directly relaxing smooth muscle (74). The drug appears to
change the physical state functions of the membrane potentials of vascular
smooth muscle cells. Both aqueous garlic and ajoene induced membrane
hyperpolarization in the cells of isolated vessel strips. The potassium
channels opened frequently causing hyperpolarization, which
resulted in vasodilation because the calcium channels were closed (75,
76). The compounds that produce the hypotensive activity of the drug are
uncertain. Allicin does not appear to be involved (43), and adenosine has
been postulated as being associated with the activity of the drug. Adenosine
enlarges the peripheral blood vessels, allowing the blood pressure to
decrease, and is also involved in the regulation of blood flow in the coronary
arteries; however, adenosine is not active when administered orally.
Bulbus Allii Sativi may increase production of nitric oxide, which is associated
with a decrease in blood pressure. In vitro studies using water or
alcohol extracts of garlic or garlic powder activated nitric-oxide synthase
(77), and these results have been confirmed by in vivo studies (78).
Aqueous garlic extracts and garlic oil have been shown in vivo to alter
the plasma fibrinogen level, coagulation time, and fibrinolytic activity
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