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The possible regulatory mechanisms of aqueous, ethyl acetate and nhexane fractions of the Ribes khorassanicum extract on acute hypertension in rats.

OBJECTIVE
Our previous studies showed the antihypertensive effect of Ribes khorassanicum (R. khorassanicum), a medicinal herb growing in the North Khorasan Province of Iran. For further evaluation, the present study investigated the effect of n-hexane (HX), ethyl acetate (EA), and aqueous (AQ) fractions of hydroalcoholic R. khorassanicum extract on cardiovascular responses in angiotensin II (AngII) and NG-nitro-L-arginine methyl ester (L-NAME) hypertensive rats.


METHODS
Wistar rats were randomly divided into 11 groups (n=5): 1) control, 2) AngII (50 ng/kg, i.v), 3) AngII + losartan (10 mg/kg, i.p), 4) L-NAME (10 mg/kg, i.v), 5) L-NAME+ sodium nitroprusside (SNP) (50 mg/kg, i.p), 6,7,8) one dose of each fraction of R. khorassanicum (AQ/EA/HX (50 mg/kg, i.p)) +AngII, and 9,10,11) one dose of each fraction of R. khorassanicum (AQ/EA/HX (50 mg/kg, i.p)) + L-NAME. Treated rats received three fractions 30 min before the injection of L-NAME and AngII in separate groups. The cardiovascular parameters were recorded by the Power Lab instrument via an angiocath inserted into the femoral artery. The peak changes (∆) of mean arterial pressure (MAP), systolic blood pressure (SBP), and heart rate (HR) in treated groups were compared with those of the hypertensive and control groups.


RESULT
AngII and L-NAME significantly increased ∆MAP and ∆SBP and attenuated by pretreatment of LOS and SNP, respectively. Pretreatment with polar (AQ) and semipolar (EA) fractions of R. khorassanicum reduced the peak changes of MAP and SBP in both AngII and L-NAME-treated groups. Only the fraction of the herb attenuated the HR increased in the L-NAME group. The HR in other groups did not demonstrate any significant difference.


CONCLUSION
All fractions of R. khorassanicum have an antihypertensive effect. However, the effect of polar fractions is more salient. It is also conceivable that the antihypertensive effect of fractions is mostly mediated by the inhibition of AngII.