The prostaglandins are endogenous 20-carbon unsaturated fatty acids biosynthetically derived from arachidonic acid. These bioactive substances and their synthetic derivatives have been of considerable research and development interest as potential therapeutic agents because of their widespread physiological and pharmacological actions on the cardiovascular system, GI smooth muscle, the reproductive system, the nervous system, platelets, kidney, the eye, etc. Prostaglandins of the E, F, and I series are found in significant concentrations throughout the GI tract. The GI actions of the prostaglandins include inhibition of basal and stimulated gastric acid and pepsin secretion in addition to prevention of ulcerogen or irritant-induced gross mucosal lesions of the stomach and intestine (termed cytoprotection). The prostaglandins can both stimulate (PGFs) and inhibit (PGEs and PGIs) intestinal smooth muscle contractility and accumulation of fluid and electrolytes in the gut lumen (PGEs). Therapeutic application of the natural prostaglandins in the treatment of GI disorders is hindered by their lack of pharmacological selectivity coupled with a less-than-optimal biodisposition profile.
Misoprostol. Misoprostol, (±)-methyl 11a, 16-dihy-droxy-16-methyl-9-oxoprost-13£-en-1-oate, is a semisynthetic derivative of PGE1 that derives some pharmacological selectivity as well as enhanced biostability from its 16-methyl, 16-hydroxy substitutions. A mixture of miso-prostol diastereomers are present in the commercial product, but most of the activity is associated with the 11r, 16S-isomer.79 Misoprostol exhibits both antisecretory and cytoprotectant effects characteristic of the natural prostaglandins and has a therapeutically acceptable biodis-
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