Agriculture Reference
In-Depth Information
Pharmacokinetics
—
Glycyrrhizin is well absorbed in the gastrointestinal tract. A clinical
evaluation with human volunteers
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used the enzyme immunoantibody technique to measure the
disposition of the compound and its aglycone.
600
It was found that the time required for maximum
serum concentration of glycyrrhizin was less than 4 h after oral administration of a decoction of
liquorice containing 133 mg of glycyrrhizin. Most of the drug was eliminated from the blood in the
majority of the cases within 72 h
.
The aglycone reached a maximum serum concentration at about
24 h, and in two of the five cases, the glycyrrhetic acid was still detected in the blood after 96 h. It
was interesting to note from the study that in the two clinical cases with symptoms of pseudoaldo-
steronism by liquorice, glycyrrhetic acid levels were up to 70-80 mg/ml, whereas the serum levels
of the glycosides were comparatively low. It is probable that pseudoaldosteronism is restricted to the
use of the aglycone and not the glycoside.
Glycyrrhizin has been shown to bind with intracellular and serum-binding proteins. In rab-
bits, the inhibitor constant values for glucocorticoid receptor binding (dissociation constant of 1.0
nmol/l) in the liver cytosol were found to be 2.0 nmol/l for glycyrrhizin and 1.7 nmol/l for glycyr-
rhetic acid, and for the mineralocorticoid receptor binding (dissociation constant = 1.1 nmol/l) in
the livercytosol, they were 3.5 nmol/l for glycyrrhetinic acid and 3.0 nmol/l for glycyrrhizin.
614
It
follows that the activity of glycyrrhizin is due, at least in part, to its effect on glucocorticoid and
mineralocorticoid receptors. The compounds did not show any significant effect on estrogen recep-
tors or serum sex hormone-binding globulin.
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Glycyrrhetinic acid hydrogen succinate (GAHS) as the disodium salt has been found to be well
absorbed by nasal instillation, and it was also observed that nasal absorption of insulin was greatly
enhanced by the presence of 1% GAHS.
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Toxicity and Adverse Reactions —
Liquorice is well tolerated, and not many serious side
effects have been reported when used within normal therapeutic dosage ranges. Most of the adverse
reactions are due to hypersensitivity to liquorice, and the few cases of toxicity have been associated
with excessive doses. Epstein and his colleagues reported a case of a woman who consumed 30 to
40 g of liquorice daily for 9 months as a starving diet to control her obesity. Her serum potassium
level fell to about 1-6 mEq/l, and her urine was dark brown and contained myoglobin. She was
reported as lethargic, with dulled reflexes, and had flaccid weakness. She also suffered from sodium
retention, which resulted in hypertension, and high aldosterone levels.
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Cumming et al. have also
reported another case of a patient who, after taking as little as 150 mg glycyrrhetic acid per week,
showed symptoms of hypokalemia (1.2 mmol/l) and flaccid quadriplegia.
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It is believed that the observed pseudoaldosteronism associated with glycyrrhizin intoxication is
due to the inhibitory effect of liquorice on 11β-hydroxysteroid dehydrogenase. The results of clini-
cal and laboratory experiments supported this conclusion.
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GNETUM AFRICANUM
Botanical Name —
Gnetum africanum
Welw.
Synonym —
Thoa africana
(Welw.) Doweld
Related Species —
Gnetum buchholzianum
Engl.
Family —
Gnetaceae
Common Names —
Gnetum, eru
African Names —
Efik (Nigeria): áfàng; Ibibio: afang; Igbo: okazi, ukazị; Yala (Ogoja, Nigeria):
eruru; Yoruba: àjáàbalè, ajakobale
Description —
Gnetum
is a dioecious liana up to 10 m long but sometimes longer; it grows
in the wild in West and Central Africa; branches are somewhat thickened at the nodes, glabrous.
Leaves are decussately opposite, sometimes in whorls of 3, and simple; stipules are absent; the
