Effect of ocular hypertension on retinal nitridergic pathway activity.
OBJECTIVE
Understanding the mechanisms of neuronal cell death in glaucoma is important for devising new treatments. Excitatory amino acids, excessive Ca(2+) influx, and formation of nitric oxide (NO) via NO synthase (NOS)-1 could be involved in glaucomatous neuropathy. The purpose of the present study was to examine the retinal nitridergic pathway activity in rats exposed to experimentally elevated intraocular pressure.


METHODS
Weekly injections of HA were performed unilaterally in the rat anterior chamber, whereas the contralateral eye was injected with saline solution. At 3 or 6 weeks of treatment, retinal NOS activity was assessed through the conversion of (3)H-L-arginine to (3)H-L-citrulline, whereas NOS-1, -2, and -3 levels were assessed by Western blotting. L-Arginine uptake was measured using (3)H-l-arginine, whereas mRNA levels of L-arginine transporters were determined by semiquantitative RT-PCR. In addition, cyclic guanosine monophosphate (cGMP) levels were quantified by radioimmunoassay.


RESULTS
At both 3 and 6 weeks of treatment, NOS activity significantly increased in HA-injected eyes although no changes in retinal NOS-1, -2, or -3 levels were observed in eyes injected with HA. L-Arginine influx and mRNA levels of cationic amino acid transporter type (CAT)-1 and -2 significantly increased in retinas from hypertensive eyes. Retinal cGMP levels significantly increased in eyes injected with HA for 3 but not 6 weeks.


CONCLUSIONS
These results suggest a significant activation of the retinal nitridergic pathway in hypertensive eyes.
Belforte
Nicolás
N
Laboratorio de Neuroquímica Retiniana y Oftalmología Experimental, Universidad de Buenos Aires, Centro de Estudios Farmacológicos y Botánicos, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
Moreno
María Cecilia
MC
Cymeryng
Cora
C
Bordone
Melina
M
Keller Sarmiento
María Inés
MI
Rosenstein
Ruth E
RE
D026923:Amino Acid Transport Systems, Basic / Q000378:metabolism; D000818:Animals; D000867:Anterior Chamber / Q000187:drug effects; D001120:Arginine / Q000378:metabolism; D015153:Blotting, Western; D002956:Citrulline / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004195:Disease Models, Animal; D006820:Hyaluronic Acid / Q000633:toxicity; D007429:Intraocular Pressure; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D009798:Ocular Hypertension / Q000139:chemically induced / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D026923:Amino Acid Transport Systems, Basic; D012333:RNA, Messenger; D002956:Citrulline; D009569:Nitric Oxide; D006820:Hyaluronic Acid; D001120:Arginine; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496322:Nos1 protein, rat; C496318:Nos2 protein, rat; C496316:Nos3 protein, rat; D006152:Cyclic GMP