The role of stomachal digestion on the pharmacological activity of plant extracts, using as an example extracts of Harpagophytum procumbens.

Various researchers have described anti-inflammatory activity of aqueous extracts of devil's-claw (Harpagophytum procumbens DC.). In this study the extent of the anti-inflammatory activity of an aqueous extract prepared from cryoground fresh plant and administered intraperitoneally, per os (by gavage), and intraduodenally was determined in rats. The anti-inflammatory properties were assessed by applying the carrageenan-induced edema test. The results obtained indicated that intraperitoneal pretreatment with an aqueous extract of H. procumbens significantly reduced the carrageenan-induced edema at 400 and 800 mg/kg 4 h after carrageenan injection (45 and 65% inhibition, respectively). When administered orally (by gavage), the extracts were inefficient. This result could be attributed to the time in transition in the stomach, where the pH is acidic, causing a decrease of the activity of the extract. This inference is consistent with the results obtained by other authors, showing the absence of extract activity when it was treated in an environment of pH 1 and 37 degrees C (similar to the physicochemical conditions found in the stomach) and then administered intraperitoneally. Intraduodenal pretreatment with the aqueous extract significantly reduced the carrageenan-induced edema at 200, 400, and 1600 mg/kg 6-9 h after carrageenan injection (43, 60, and 41% inhibition, respectively). The presence of extract activity after intraduodenal administration supports the assumption that transition of the extract through the stomach leads to loss of activity.