EXPOSURE TO ALTERNATING HYPOXIA AND HYPEROXIA CAUSES SEVERE PROLIFERATIVE RETINOPATHY IN THE NEWBORN RAT

Exposure to variable hyperoxia has recently been shown to be much more effective at producing proliferative retinopathy in the newborn rat t han exposure to constant hyperoxia. To incorporate a more clinically r elevant oxygen-exposure paradigm in our studies, we have now used a cy cle between 50 and 10% oxygen and have compared its effects with those found using new exposures to the previously used 80/40% cycle. Starti ng at birth and continuing for 14 d, rats were exposed to environments that cycled between 50 and 10% oxygen or 80 and 40% oxygen every 24 h . After exposure, some rats were killed for assessment of retinal vasc ular development. Others were removed to room air for 4 d before killi ng and evaluation for the presence of abnormal neovascularization-a cl inical consequence believed to be promoted by termination of oxygen th erapy. The 50/10% cycle resulted in greater retardation of retinal blo od vessel development during oxygen than that found in the 80/40% expo sure group. After 4 d postexposure in room air, the incidence of prere tinal neovascularization was 97% in the 50/10% rats and 72% in the 80/ 40% group. Clearly, the overall amount of oxygen the subject receives is less critical than other parameters of its administration in produc ing proliferative retinopathy. Also, the range of variation (40% in bo th cases) is not the controlling characteristic. Our results suggest t hat consistency of oxygen level and avoidance of hypoxic levels should be important concerns in neonatal oxygen therapy.