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R.E. Rosenstein, G.B. Sacca, L. Minces, C.O. Jaliffa, M.I. Keller Sarmiento, D.A. Saenz; Photic Regulation of Heme Oxygenase Activity in the Golden Hamster Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4571.
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Purpose: To study the photic regulation of heme oxygenase activity in the golden hamster retina. Methods: Heme oxygenase (HO) activity was assessed by a spectrophotometric assay. Western blotting was employed to identify retinal HO isoforms and to assess their levels. Retinal levels of cGMP were measured by radioimmunoassay, whereas retinal thiobarbituric acid reactive substances (TBARS) levels were assessed spectrophometricaly Results: HO activity was significantly higher at midday than at midnight. When the hamsters were placed under constant darkness for 48 h and killed at subjective day or at subjective night, the differences in HO activity disappeared. Western blot analysis showed no differences in HO-2 levels among these time points, whereas HO-1 was not detected at any interval. Dopamine significantly increased HO activity in retinas excised at noon or at midnight, with a higher sensitivity during the night. The effect of dopamine was reversed by SCH 23390 but not by spiperone and clozapine and it was not reproduced by quinpirole. Two cAMP analogues (8 Br and dibutyryl-cAMP) increased HO activity being their effect as well as the effect of dopamine blocked by H-89, a PKA inhibitor. Tin-protoporphyrin IX, an HO inhibitor, significantly decreased cGMP accumulation with maximal effects during the day. Low concentrations of bilirubin decreased retinal thiobarbituric acid substances levels (an index of lipid peroxidation) in basal conditions and after exposing retinal cells to H2O2. Conclusions: These results suggest that hamster retinal HO activity is regulated by the photic stimulus, probably through a dopamine/cAMP/PKA dependent pathway. In addition, present results support that HO activity could be involved in retinal physiology and pathology.
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