Prostaglandin I ₂ Contributes to the Vasodepressor Effect of Baicalein in Hypertensive Rats

Abstract

Abstract-Lipoxygenase inhibitors reduce blood pressure in hypertensive rats. The vasodepressor effect of lipoxygenase inhibitors may be related to increased production of prostaglandin (PG) I 2 since lipoxygenase-derived fatty acid hydroperoxides inhibit PGI 2 synthase. This hypothesis was examined in rats made hypertensive by infusion of angiotensin II (200 ng/min IP) for 12 to 14 days. In hypertensive but not in normotensive rats, the lipoxygenase inhibitor baicalein (60 mg/kg SC) increased (PϽ.05) the conversion of exogenous PGH 2 to PGI 2 by aortic segments, the release of 6-keto-PGF 1␣ by aortic rings, the concentration of 6-keto-PGF 1␣ in blood, and the renal excretion of 6-keto-PGF 1␣ . Treatment with baicalein did not affect the blood pressure of normotensive rats but decreased the blood pressure of hypertensive rats from 177Ϯ8 to 133Ϯ9 mm Hg after 120 minutes (PϽ.05). Also, the lipoxygenase inhibitor cinnamyl-3,4-dihydroxy-␣-cyanocinnamate (8 mg/kg SC) was without effect on the blood pressure of normotensive rats but decreased the blood pressure of hypertensive rats from 182Ϯ4 to 139Ϯ8 mm Hg (PϽ.05). However, the blood pressure of hypertensive rats pretreated with indomethacin (5 mg/kg IV) was affected by neither baicalein nor cinnamyl-3,4-dihydroxy-␣-cyanocinnamate. Moreover, in hypertensive rats in which baicalein had decreased blood pressure to 148Ϯ6 mm Hg, the administration of rabbit serum containing antibodies against 5,6-dihydro-PGI 2 (0.3 mL IV) partially reversed the response to baicalein, increasing blood pressure to 179Ϯ7 mm Hg within 20 minutes (PϽ.05). The antibodies also were shown to block the vasodepressor effect of PGI 2 but not of PGE 2 . Collectively, these data suggest contribution of PGI 2 to the acute antihypertensive effect of baicalein in rats with angiotensin II-induced hypertension.

Inhibitory activities of baicalin against renin and angiotensin-converting enzyme

“…In addition, the vasodepressor effect of baicalin has been previously reported in rats (Takizawa et al, 1998). The results of this study revealed that baicalin is more potent in renin inhibition than ACE inhibition, similar to the activity of sodium houttuyfonate analogs (Yuan et al, 2006), suggesting that baicalin, formerly an antimicrobial and antiviral agent, may interfere the RAS in vivo through renin and ACE inhibitions.…”

Nitric oxide dilates rat retinal blood vessels by cyclooxygenase-dependent mechanisms

“…In this protocol, the responses to NOR3 (30 g ⅐ kg Ϫ1 ⅐ min Ϫ1 iv) determined before and after treatment with indomethacin (5 mg/kg iv), SC-560 (5 mg/kg iv), NS-398 (5 mg/kg ip), or nimesulide (1 mg/kg iv) were compared. The doses of COX inhibitors were chosen on the basis of previous reports (1,7,31).…”

Immunostimulant Activity ofn-Butanol Fraction of Root Bark ofOroxylum indicum, vent.

“…Antiinflammatory, anti-HIV, anti-cancer, and anti-oxidant activities have all been reported for baicalein in in vitro studies using cell lines (reviewed in Lai et al, 2003). In vivo studies in rats have indicated that this agent also possesses anti-inflammatory and vasodepressor effects (Lin and Shieh, 1996;Takizawa et al, 1998).…”