Objective    To investigate the effects of different oxygen inhalation modes on retinal vessels development in neonatal rat in order to approach its etiopathogenesis and provide experimental evidence for proper oxygen therapy for premature.     Methods    Totally 150 postnatal day 7 (P7) Wistar rats were randomly assigned into 5 groups according to different oxygen inhalation modes (n=30 in each group). Experimental group 1 were exposed to 75%

60%

50%

40% and 30% oxygen in turn for one day

followed by room air exposure for 5 d. Experimental group 2 were exposed to 30%

40%

50%

60% and 75% oxygen in turn for one day

then exposed in air for 5 d. Experimental group 3 were exposed to 75% oxygen for 5 d

then oxygen supply was suddenly stopped

followed by room air exposure for 5 d. Experimental group 4 were exposed to 75% oxygen for 5 d

then the oxygen supply was reduced by 10% per day till oxygen supply level equal to room air

finally room air exposure for 5 d. The control group were exposed to room air in the same experimental condition. The retinal vascular development and proliferation were evaluated by stretched preparation (ADPase stained retina) and eyeball cross-section. The nuclei of proliferative retinal vessels of 5 groups were counted and the vascular endothelial growth factor (VEGF) expressions in retina were detected by immunohistochemical staining. The dependability between the nuclei of proliferative retinal vessels and the VEGF expressions in retina were also analyzed.     Results    In the experimental groups 2 and 3

there existed retinal hypoxia and formed abnormal new vessels as retinopathy of prematurity (ROP). The VEGF expressions increased after hypoxia

mainly in endochylema and nucleus of capillary endothelium of ganglionic layer of retina and inner nuclear layer. Linear correlation analysis of the data indicated the positive correlation was between the nuclei of the proliferative vessels and the VEGF levels in retina (r=0.807

P0.01).     Conclusion    Abrupt quit of oxygen supply contributes to the development of retinal vessels in neonatal rats and induces pathological changes of retina as ROP. So we should monitor oxygen concentration intimately in clinic and adopt the mode of gradually reducing oxygen supply.