PURPOSE: Production of NO may be regulated by argininosuccinate synthetase and argininosuccinate lyase which recycle citrulline to arginine, and by arginase which hydrolyzes arginine to urea and ornithine. Expression of these and related enzymes in rat eye was studied. METHODS: mRNAs for the enzymes were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Localization of the enzyme proteins and mRNAs was analyzed by immunohistochemistry and in situ hybridization, respectively. RESULTS: In RT-PCR analysis, arginase II (nonhepatic type) mRNA was detected in retina and weakly in cornea, whereas arginase I (hepatic type) mRNA was not detected in any area. mRNAs for argininosuccinate synthetase, argininosuccinate lyase, ornithine aminotransferase and ornithine decarboxylase were present in all areas. In immunohistochemical analysis, arginase II was stained in cornea, epithelium of iris and ciliary process, inner part of neural retina and retinal pigment epithelium. Immunostaining of ornithine aminotransferase resembled that of arginase II. In in situ hybridization, arginase II and ornithine aminotransferase mRNAs were located much as seen with the enzyme proteins. CONCLUSIONS: These results indicate that arginine recycling activity from citrulline is present widely in ocular tissues, whereas expression of arginase II differs among the tissues. We suggest that NO production may be regulated by these enzymes in the cells where NO synthase is colocalized. Colocalization of arginase II and ornithine aminotransferase suggests a role for arginase II in collagen synthesis in the eye.
PURPOSE: Production of NO may be regulated by argininosuccinate synthetase and argininosuccinate lyase which recycle citrulline to arginine, and by arginase which hydrolyzes arginine to urea and ornithine. Expression of these and related enzymes in rat eye was studied. METHODS: mRNAs for the enzymes were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Localization of the enzyme proteins and mRNAs was analyzed by immunohistochemistry and in situ hybridization, respectively. RESULTS: In RT-PCR analysis, arginase II (nonhepatic type) mRNA was detected in retina and weakly in cornea, whereas arginase I (hepatic type) mRNA was not detected in any area. mRNAs for argininosuccinate synthetase, argininosuccinate lyase, ornithine aminotransferase and ornithine decarboxylase were present in all areas. In immunohistochemical analysis, arginase II was stained in cornea, epithelium of iris and ciliary process, inner part of neural retina and retinal pigment epithelium. Immunostaining of ornithine aminotransferase resembled that of arginase II. In in situ hybridization, arginase II and ornithine aminotransferase mRNAs were located much as seen with the enzyme proteins. CONCLUSIONS: These results indicate that arginine recycling activity from citrulline is present widely in ocular tissues, whereas expression of arginase II differs among the tissues. We suggest that NO production may be regulated by these enzymes in the cells where NO synthase is colocalized. Colocalization of arginase II and ornithine aminotransferase suggests a role for arginase II in collagen synthesis in the eye.