title: Contribution of nitric oxide synthase isoforms to cholinergic vasodilation in murine retinal arterioles.
abstract: Nitric oxide synthases (NOSs) are critically involved in regulation of ocular perfusion. However, the contribution of the individual NOS isoforms to vascular responses is unknown in the retina. Because some previous findings suggested an involvement of inducible nitric oxide synthase (iNOS) in the regulation of retinal vascular tone, a major goal of the present study was to examine the hypothesis that iNOS is involved in mediating cholinergic vasodilation responses of murine retinal arterioles. Another subject of this study was to test the contribution of the other two NOS isoforms, neuronal (nNOS) and endothelial NOS (eNOS), to cholinergic retinal arteriole responses. Expression of individual NOS isoforms was determined in murine retinal arterioles using real-time PCR. All three NOS isoforms were expressed in retinal arterioles. However, eNOS mRNA was found to be most, and iNOS mRNA least abundant. To examine the functional relevance of iNOS for mediating vascular responses, retinal vascular preparations from gene-targeted iNOS-deficient mice (iNOS-/-) and wild-type mice were studied in vitro. Changes in luminal vessel diameter in response to the thromboxane mimetic 9,11-dideoxy-9α,11α-methanoepoxy prostaglandin F2α (U-46619), the endothelium-dependent vasodilator acetylcholine, and the nitric oxide donor nitroprusside were measured by video microscopy. To determine the contribution of individual NOS isoforms to cholinergic vasodilation responses, retinas from iNOS-/- and wild-type mice were incubated with Nω-nitro-l-arginine methyl ester (l-NAME), a non-isoform-selective inhibitor of NOS, 7-nitroindazole, a selective nNOS blocker and aminoguanidine, a selective iNOS inhibitor. U-46619 evoked concentration-dependent vasoconstriction that was similar in retinal arterioles from iNOS-/- and wild-type mice. In retinal arterioles preconstricted with U-46619, acetylcholine and nitroprusside produced dose-dependent dilation that did not differ between iNOS-/- and wild-type mice. Remarkably, in both genotypes, vasodilation to acetylcholine was negligible after incubation with l-NAME. In contrast, pharmacological inhibition of nNOS and iNOS had no effect on acetylcholine-induced vasodilation. These findings suggest that dilation of murine retinal arterioles to acetylcholine is mediated predominantly by eNOS.
authors: Department of Ophthalmology, University Medical Center, Johannes Gutenberg University Mainz, Langenbeckstr. 1, 55131 Mainz, Germany. adrian.gericke@gmx.net
authors: Adrian
authors: A
authors: Gericke
authors: Evgeny
authors: E
authors: Goloborodko
authors: Jan J
authors: JJ
authors: Sniatecki
authors: Andreas
authors: A
authors: Steege
authors: Leszek
authors: L
authors: Wojnowski
authors: Norbert
authors: N
authors: Pfeiffer
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000201:enzymology*; D001921:Brain / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009599:Nitroprusside / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D012171:Retinal Vessels / Q000187:drug effects / Q000201:enzymology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D014665:Vasodilator Agents; D009599:Nitroprusside; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496321:Nos1 protein, mouse; C496317:Nos2 protein, mouse; C496315:Nos3 protein, mouse; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester