Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil.
Invest Ophthalmol Vis Sci. 2011 Sep 22;52(10):7416-22. doi: 10.1167/iovs.10-6756.
Retinal melatonin synthesis occurs in the photoreceptor layer in a circadian manner, controlling several physiologic rhythmic phenomena, besides being the most powerful natural free radical scavenger. The purpose of the present work was to evaluate the diurnal profile of retinal melatonin content and the regulation of its synthesis in the retina of streptozotocin-induced diabetic rats.
Diabetes was induced in male Wistar rats (12 hour-12 hour light/dark cycle) with streptozotocin. Control, diabetic, and insulin-treated diabetic animals were killed every 3 hours throughout the light-dark cycle. Retinal melatonin content was measured by high-performance liquid chromatography, arylalkylamine N-acetyltransferase (AANAT) activity was analyzed by radiometric assay, Bmal1 gene expression was determined by qPCR, and cyclic adenosine monophosphate (cAMP) content was assessed by ELISA.
Control animals showed a clear retinal melatonin and AANAT activity daily rhythm, with high levels in the dark. Diabetic rats had both parameters reduced, and the impairment was prevented by immediate insulin treatment. In addition, the Bmal1 expression profile was lost in the diabetic group, and the retinal cAMP level was reduced 6 hours after lights on and 3 hours after lights off.
The present work shows a melatonin synthesis reduction in diabetic rats retinas associated with a reduction in AANAT activity that was prevented by insulin treatment. The Bmal1-flattened gene expression and the cAMP reduction seem to be responsible for the AANAT activity decrease in diabetic animals. The melatonin synthesis reduction observed in the pineal gland of diabetic rats is also observed in a local melatonin tissue synthesizer, the retina.
视网膜中的褪黑素以昼夜节律的方式合成，除了作为最强大的天然自由基清除剂外，还控制着几种生理节律现象。本研究旨在评估视网膜褪黑素含量的昼夜节律变化，并研究糖尿病大鼠视网膜中褪黑素合成的调节。
使用链脲佐菌素诱导雄性 Wistar 大鼠（12 小时-12 小时光照/黑暗周期）产生糖尿病。每隔 3 小时，在整个光照-黑暗周期内，处死对照组、糖尿病组和胰岛素治疗的糖尿病组动物。通过高效液相色谱法测量视网膜褪黑素含量，通过放射性测定法分析芳香族烷基胺 N-乙酰基转移酶（AANAT）活性，通过 qPCR 测定 Bmal1 基因表达，通过 ELISA 测定环磷酸腺苷（cAMP）含量。
对照组动物表现出明显的视网膜褪黑素和 AANAT 活性昼夜节律，黑暗时水平较高。糖尿病大鼠这两种参数均降低，胰岛素治疗可预防这种损害。此外，糖尿病组的 Bmal1 表达谱丢失，并且在光照后 6 小时和光照后 3 小时，视网膜 cAMP 水平降低。
本研究表明，糖尿病大鼠视网膜褪黑素合成减少与 AANAT 活性降低有关，而胰岛素治疗可预防这种情况。Bmal1 基因表达的平坦化和 cAMP 的减少似乎是糖尿病动物中 AANAT 活性降低的原因。在糖尿病大鼠的松果体中观察到的褪黑素合成减少也发生在局部褪黑素组织合成器——视网膜中。
