Rod outer segment membranes (ROS) are highly vulnerable to autooxidation because of their high content of long chain polyunsaturated fatty acids (PUFAs). Melatonin and N-acetylserotonin are indoleamines synthesized in the pineal gland, retina and other tissues. These compounds are free radical scavengers and indirect antioxidants because of their stimulatory effect on antioxidative enzymes. We compared the in vitro protective effect of melatonin and N-acetylserotonin on the ascorbate-Fe2+ induced lipid peroxidation of PUFAs located in ROS membranes. This process was measured by chemiluminescence and fatty acid composition of total lipids of ROS. We assayed increasing concentrations of melatonin (0-10 mm) and N-acetylserotonin (0-2 mm). In both cases the total cpm originated from light emission (chemiluminescence) was found to be lower in those membranes incubated in the presence of either melatonin or N-acetylserotonin; this decreased proportional to the concentration of the indole. Thus, 10 mm melatonin and 2 mm N-acetylserotonin produced a reduction of 51 +/- 6 and 100% in the total chemiluminescene (lipid peroxidation), respectively. We also noticed a PUFAs protection: the docosahexaenoic acid content decreased considerably when the membranes were submitted to oxidative damage. This reduction was from 37.6 +/- 2.1% in the native membranes to 6.2 +/- 0.8% in those which were peroxidized. These changes were less pronounced in treated ROS membranes; as an example in the presence of 10 mm melatonin or 2 mm N-acetylserotonin we observed a content preservation of 22:6 n-3 (23.6 +/- 1.2 and 39.1 +/- 1.2% respectively). The concentration of each compound required to inhibit 50% of the lipid peroxidation (IC50) was 9.82 mm for melatonin and 0.43 mm for N-acetylserotonin, respectively. N-acetylserotonin shows a protective effect about 20 times higher than that of melatonin.

中文翻译：

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吲哚胺对牛视网膜视网膜杆外节膜的抗坏血酸-Fe2 +依赖性脂质过氧化的保护作用。

杆外段膜（ROS）由于其高含量的长链多不饱和脂肪酸（PUFA）高度易受自氧化作用。褪黑素和N-乙酰羟色胺是在松果体，视网膜和其他组织中合成的吲哚胺。这些化合物是自由基清除剂和间接抗氧化剂，因为它们对抗氧化酶具有刺激作用。我们比较了褪黑素和N-乙酰5-羟色胺对抗坏血酸-Fe2 +诱导的位于ROS膜上的PUFA脂质过氧化的体外保护作用。通过化学发光和ROS总脂质的脂肪酸组成来测量该过程。我们测定了褪黑激素（0-10毫米）和N-乙酰羟色胺（0-2毫米）浓度的增加。在这两种情况下，发现在褪黑素或N-乙酰5-羟色胺存在下孵育的那些膜中，源自发光（化学发光）的总cpm较低。这与吲哚的浓度成比例地降低。因此，10毫米褪黑素和2毫米N-乙酰5-羟色胺的总化学发光率（脂质过氧化）分别降低了51 +/- 6和100％。我们还注意到了PUFA的保护作用：当膜遭受氧化损伤时，二十二碳六烯酸的含量大大降低。这种降低从天然膜的37.6 +/- 2.1％降至过氧化膜的6.2 +/- 0.8％。这些变化在处理过的ROS膜中不那么明显。例如，在10毫米褪黑素或2毫米N-乙酰5-羟色胺存在的情况下，我们观察到22：6 n-3的含量保持率（23。分别为6 +/- 1.2和39.1 +/- 1.2％）。抑制50％脂质过氧化（IC50）所需的每种化合物的浓度，褪黑激素分别为9.82毫米和N-乙酰羟色胺为0.43毫米。N-乙酰血清素显示出比褪黑素高约20倍的保护作用。