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The Role of Nitric Oxide and cGMP in Somatostatin’s Protection against Retinal Ischemia

From the Laboratory of Pharmacology, Department of Basic Sciences, Faculty of Medicine, University of Crete, Heraklion, Crete, Greece.

PURPOSE. To investigate whether nitric oxide (NO) and/or cGMP protects the retina from chemical ischemia and underlie somatostatin’s neuroprotective effects.

METHODS. Eyecups of female Sprague-Dawley rats were incubated with PBS or the chemical ischemia mixture [iodoacetic acid (5 mM)/sodium cyanate (25 mM)] in the absence or presence of (1) arginine (0.05–2.0 mM), the substrate of nitric oxide synthase (NOS); (2) the NO donors sodium nitroprusside (SNP; 0.25–4.0 mM), 3-morpholinosydnonimine (SIN-1; 0.1, 0.3, 1.0 mM), SIN-1 (0.1 mM)/L-cysteine (5 mM, peroxynitrite scavenger), and NONOate (1, 5, 10 µM, slow NO releaser); (3) 8-Br-cGMP (0.1, 0.5, 1.0 mM); (4) BIM23014 (sst₂ receptor agonist; 1 µM), alone or in the presence of (5) the NOS inhibitor N-monomethyl-L-arginine (NMMA; 0.5 mM); or (6) the guanylyl cyclase inhibitors 1H-[1,2,4]oxadiazolol [4,3-a]quinoxalin-1-one (ODQ;100 µM) and NS2028 (50 µM) for 60 minutes, at 5%CO₂/air in 37°C. The effect of SIN-1 (0.1, 0.3, 1.0, or 3.0 mM) on the retina was also examined. Subsequently, the eyecups were fixed and sectioned for choline acetyltransferase (ChAT) immunoreactivity and TUNEL staining.

RESULTS. Arginine and SNP had no effect on the chemical ischemia–induced toxicity. SIN-1, NONOate, and 8-Br-cGMP produced a concentration-dependent protective effect, as shown by ChAT immunoreactivity. TUNEL staining also confirmed the neuroprotective effect of these agents. L-Cysteine partially reduced the SIN-1–induced protective effect. SIN-1 alone was toxic only at the highest concentration used (3 mM). NMMA, ODQ, and NS2028 reversed the protective effect of BIM23014.

CONCLUSIONS. The results suggest that a NO/peroxynitrite/cGMP mechanism may be important in the protection of the retina from ischemic insult. Furthermore, the NO/sGC/cGMP pathway is involved in the neuroprotective effects of sst₂ ligands against retinal ischemia.

This article has been cited by other articles:

				F. Kiagiadaki and K. Thermos Effect of Intravitreal Administration of Somatostatin and sst2 Analogs on AMPA-Induced Neurotoxicity in Rat Retina Invest. Ophthalmol. Vis. Sci., July 1, 2008; 49(7): 3080 - 3089. [Abstract] [Full Text] [PDF]