A Major Role for Prostacyclin in Nitric Oxide–Induced Ocular Vasorelaxation in the Piglet

Abstract—We studied the mechanisms of retinal and choroidal vasorelaxation elicited by nitric oxide (NO) using piglet eyes. The NO donors sodium nitroprusside (SNP) and diethylamine-NONOate caused comparable concentration–dependent relaxation that was partially (≈40%) attenuated by the guanylate cyclase inhibitors methylene blue and LY83583 and reduced to a lesser extent (≈25%) by the inhibitor of cGMP–dependent kinase, KT 5823. In contrast, NO-induced dilatation (by NO donors and endogenous NO after stimulation with bradykinin) was substantially (≈70%) diminished by the KCa channel blockers tetraethylammonium (TEA), charybdotoxin, and iberiotoxin; by the cyclooxygenase inhibitors indomethacin and ibuprofen; by the prostaglandin I (PGI2) synthase inhibitor trans-2-phenyl cyclopropylamine (TPC); and by the removal of endothelium; whereas relaxation of endothelium-denuded vasculature to SNP was unaltered by indomethacin, TPC, and charybdotoxin but was nearly nullified by methylene blue and the Kv channel bl...