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BACKGROUND: Apoptosis of retinal photoreceptor cells is a commonly pathological characteristic of various eye diseases, while caspase-3 is an important regulating gene and plays a key role in apoptosis. OBJECTIVE: To measure the expression of caspase-3 mRNA in rats with apoptosis of retinal photoreceptor cells by using real-time fluorescent quantitative polymerase chain reaction and compare with those of the normal rats.DESIGN: Randomized controlled animal study.SETTING: Zhongshan Ophthalmological Center of Sun Yat-sen University.MATERIALS: A total of 36 female SD rats of 50 days old and clean grade and weighing (150±10) g were provided by Experimental Animal Center of Northern Area of Sun Yat-sen University. All rats were randomly divided into normal control group (n =6) and N-methyl-N-nitrosourea (MNU) group (n =30), and they were observed at 12 hours, 1, 2, 3 and 5 days after model establishment, with 6 rats at each time point. METHODS: The experiment was carried out at Zhongshan Ophthalmological Center, Key Laboratory of Ophthalmology by State Ministry of Education from March to December 2004. Rats in the normal control group were intraperitoneally injected with saline and rats in the MNU group were intraperitoneally injected with 40 mg/kg MNU. And then, retinal photoreceptor injured models were established. At 12 hours, 1, 2, 3 and 5 days after model establishment, the rats were sacrificed for enucleating right eyeballs, isolating retina immediately and extracting total RNA. The expression of caspase-3 mRNA in retina was measured with real-time fluorescent quantitative polymerase chain reaction.MAIN OUTCOME MEASURES: Expression of caspase-3 mRNA in retina of rats in the two groups. RESULTS: A total of 36 SD rats were involved in the final analysis. The expressions of caspase-3 mRNA in the rat retina of both groups at the five time points (12 hours, 1, 2, 3 and 5 days) after model establishment were 1.52×105, 18.35×105, 25.14×105, 29.25×105, 13.72×105 and 12.24×105, respectively. The expression of caspase-3 mRNA in the MNU group increased after 12 hours of intraperitoneal injection, and rose to the top on the 2nd day, which was 19 times as many as that of the normal control group. Then, it decreased gradually and was still 8 times as many as that of the normal control group on the 5th day.CONCLUSION: The expression of caspase-3 mRNA is related to apoptosis of retinal photoreceptor cells,while caspase-3 plays an important role in occurrence and development of apoptosis of retinal photoreceptor cells.