5' nucleotidase and adenosine during retinal vasculogenesis and oxygen-induced retinopathy

5' nucleotidase (5'N) is a major source of the vasogenic substance adenosine in most tissues. The distribution and relative levels of 5'N and adenosine were examined in neonatal dog inner retina during normal vasculogenesis and oxygen-induced retinopathy (OIR).

Animals ranging in age from 1 to 22 days of age were used in this study. Adenosine immunolocalization was performed on frozen sections with an antibody against adenosine conjugated to laevulinic acid using a streptavidin peroxidase technique. Triplicate room air control animals at different postnatal ages and triplicate oxygen-treated animals at different time points during or after hyperoxic insult were analyzed. Adenosine immunoreactivity (AI) and 5'N enzyme histochemical reaction product were quantified using microdensitometry. Adjacent sections were incubated for von Willebrand factor to label blood vessels.

During normal vasculogenesis, AI was most prominent within the inner retina. The peak of immunoreactivity was located at the border of vascularized retina throughout the period of primary retinal vasculogenesis (1-15 days of age). At 22 days when vasculogenesis was complete, AI decreased within the inner retina. The highest 5'N activity was localized to inner Muller cell processes in inner retina and decreased after vasculogenesis was complete. In animals killed after 4 days of oxygen breathing, the vasoobliterative stage of OIR, AI and 5'N activity were reduced throughout the retina. During the vasoproliferative stage, AI was markedly elevated at the edge of reforming vasculature as well as throughout the more posterior inner retina where 5'N activity also was elevated. AI was also in intravitreal neovascularization.

Peak adenosine levels in the inner retina correlated temporally with active vasculogenesis. Adenosine and 5'N levels were reduced in hyperoxia and then returned to above normal levels during the vasoproliferative stage of OIR.