Angiotensin-II contracts isolated human posterior ciliary arteries.
The effect of angiotensin-II (A-II) was studied on ring segments of the terminal extraocular branches of the posterior ciliary artery isolated from human enucleated eyes. It induced a potent concentration-dependent contraction on top of the spontaneous myogenic tone of all arteries studied from five patients with the concentration required to give half-maximal response equal to 51 nM. The spontaneous tone and maximal increase in vessel wall tension induced by A-II was equal to 51% of Emax. The relative response and sensitivity to A-II was unchanged in three endothelial denuded vessels, but the spontaneous tone increased. The arteries became completely insensitive to A-II after one exposure. These results show an immediate direct contractile effect of A-II on human posterior ciliary arteries, but the development of pronounced tachyphylaxis indicates that A-II is probably not an important factor in reducing blood flow to the optic nerve head.
Nyborg
N C
NC
Department of Pharmacology, Aarhus University, Denmark.
Nielsen
P J
PJ
D000368:Aged; D000804:Angiotensin II / Q000502:physiology*; D001158:Arteries / Q000502:physiology; D002924:Ciliary Body / Q000098:blood supply* / Q000187:drug effects; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D010208:Papaverine / Q000494:pharmacology; D014661:Vasoconstriction / Q000502:physiology*
D000804:Angiotensin II; D010208:Papaverine