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D. M. Silberman, M. I. Keller Sarmiento, R. E. Rosenstein; Circadian Variations of Prostaglandin E2 and F2alpha Levels in the Golden Hamster Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2943.
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The mammalian retina contains an endogenous circadian pacemaker that broadly regulates retinal physiology and function, although the cellular origin and organization of the mammalian retinal circadian clock remains unclear. Recently, it was demonstrated that prostaglandin E2 (PGE2), a proinflammatory compound known to have diverse biological effects in several systems including the retina, is able to act as an in vivo clock-resetting agent. Based on the putative link between prostaglandins and circadian clock activity, the aim of the present work was to study circadian variations of prostaglandins levels in the hamster retina.
Male golden hamsters (Mesocricetus auratus) kept under a photoperiod of 14 h of light- 10 h of darkness with free access to food and water were used throughout. In some experiments, animals were moved into constant darkness for 48 h before the experiments. Retinas were excised at midday, midnight, subjective midday or subjective midnight and incubated for 1 hour. PGE2 and prostaglandin F2α (PGF2α) secretion was assessed by radioimmunoassay. Retinal COX-1 and COX-2 levels were examined by Western blotting.
PGE2 and PGF2α production was significantly higher (p < 0.01) in retinas excised at midnight than at midday. Daily variations in retinal prostaglandin levels persisted in golden hamsters exposed to constant darkness. COX-1 levels were significantly higher at midnight than at midday and at the subjective night than at the subjective day, while no changes in COX-2 levels were observed.
For the first time, these results support the idea of a circadian clock-controlled prostaglandin synthesis in the hamster retina. In addition, our results support the possibility that retinal prostaglandins, as a mediating component of the ocular rhythm generator, may be involved in retinal circadian rhythmicity, being a part of the mechanisms underlying the temporal regulation of retinal physiology.
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