Pineal Gland: N3 and N6 Essential Fatty Acids, Lipoxygenation and Melatonin Synthesis

ANGEL CATALA

Pineal Gland: Research Advances and Clinical Challenges

Nova Science Publishers

Lugar: Hauppauge NY ; Año: 2017; p. 1 - 345

The mammalian pineal gland is an important secretor organ with a high metabolic activity. There is a daily rhythm in the production of the pineal hormone melatonin in all mammalian species. In vertebrates, the retina and the pineal gland play a critical function in the transduction of the photoperiodic and thermoperiodic (ectotherms only) information. Additionally, both organs produce melatonin, one major output of the circadian clocks. Melatonin (N-acetyl-5-methoxytryptamine), the main secretory product of the pineal gland, efficiently scavenges both the hydroxyl and peroxyl radicals neutralizing lipid peroxidation in biological membranes. The pineal gland contains high levels of n-3 and n-6 PUFAs. It has been reported that at least 25% of the total fatty acids identified in the rat pineal lipids are represented by arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3). These very long chain polyunsaturated fatty acids play important roles in the pineal gland. In addition to the production of melatonin, the mammalian pineal gland is able of convert these polyunsaturated fatty acids into bioactive lipid mediators. Lipoxygenation is the principal lipoxygenase (LOX) activity observed in the rat pineal gland. Lipoxygenation in the pineal gland is exceptional because no other brain regions express significant LOX activities under normal physiological conditions. The rat pineal gland expresses both 12- and 15-lipoxygenase activities, producing 12- and 15-hydroperoxyeicosatetraenoic acid (12- and 15-HpETE) from arachidonic acid and 14- and 17-hydroxydocosahexaenoic acid (14- and 17-HdoHE) from docosahexaenoic acid, respectively. The rat pineal also produces hepoxilins via LOX pathways. The hepoxilins are bioactive epoxy-hydroxy products of the arachidonic acid metabolism via the 12S-lipoxygenase (12S-LOX) pathway. The two key pineal biochemical functions, lipoxygenation and melatonin synthesis, may be synergistically regulated by the status of n-3 essential fatty acids.