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The principal active constituents of senna are dimeric glycosides called SENNOSIDES A, B, C, and D. The aglycones are composed of aloe-emodin + rhein for A and B and rhein + rhein for C and D.
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The Sennosides are water soluble but the meso form is more soluble than the trans form. All the four glycosides are responsible for the activity of senna. The two methods used to assay senna are: the Borntrager assay and the mice assay.
Consists of taking sample of plant and heating it to 100 deg.C. for 30 min. with 2M HCl. Cool and extract into CCl4 (carbon tetrachloride). The HCl hydrolyses off the sugar leaving the aglycone which then dissolves in CCl4. Take the CCl4 solution with dissolved aglycone and shake with KOH soln. This gives a purple color. Color intensity is proportional to concentration of anthracene. The purple color is due to the
anthracene which includes both active dimers and inactive derivatives.
Two sets of mice under equal conditions are tested. One set is given the drug and the other placebo or just water. The droppings are then measured and compared.
The anthraquinone glycosides pass unchanged into the colon where
bacteria hydrolyse the glycoside bond yielding the free anthraquinones which has a direct stimulant effect on the
myenteric plexus, resulting in smooth muscle activity and thus defaecation.
Some of the drug is also absorbed and excreted in the urine and may appear in breast milk. There is evidence to suggest that long-continued use of anthroquinone purgatives results in damage to the myenteric plexus. Long term use or misuse can result in dependency and electrolyte loss. Senna should not be used during pregnancy or lactation.
FRIEDLI ENTERPRISESBorntrager Assay
Mice Assay
PHARMACOLOGY
Georges-Louis Friedli, PgDip., MSc., Ph.D.
georges-louis@friedli.com