Modulation by endothelium of the vascular effects of angiotensin II.

Modulation by vascular endothelium of the effects of AII was studied in the isolated rabbit aortic and superior mesenteric artery strips. The contractile effect of AII was enhanced in rubbed aortic strips. Similar enhancement was obtained in hydroquinone pretreated unrubbed strips. The relaxing effect of acetylcholine in AII--induced precontracted aortic strips was abolished after rubbing and hydroquinone pretreatment. However, no significant changes were observed in the contractile response to AII on aspirin and nicotine pretreated strips. In the isolated mesenteric artery strips AII produced a biphasic responses. The contractile effect of AII was enhanced in rubbed strips. Similar potentiation was also obtained in hydroquinone, aspirin and nicotine pretreated unrubbed strips. The relaxation phase of AII response was completely abolished in rubbed strips but partially inhibited in hydroquinone, aspirin and nicotine pretreated unrubbed strips. From these results it was concluded that EDRF is the main endothelial humoral factor which modulates the effect of AII in the rabbit aorta while both EDRF and PGI2 are involved for the modulation of the effects of octapeptide in the mesenteric artery.