Back in 2012, the American Physiological Society put together an amazing list of the top ten articles cited in each of their journals every quarter of a century in honor of their 125th anniversary. In looking through the website this week, I stumbled upon this collection and was reminded about the amazing early foundational work and excellence in physiology research found within this body of work. So, I’d like to take a step back in time to highlight some of these foundational studies in a new theme: “Time Machine”. It is only appropriate that we begin this journey talking about the hormone melatonin.
In 1991, Dr. Russel Reiter published an article in Physiology in which he described the various actions of the hormone, melatonin. Blood levels of melatonin vary throughout the day with levels highest at night. The circadian rhythm of melatonin helps regulate sleep-wake cycles in vertebrates. Exposure to light triggers a reduction in melatonin, which is one reason why light at night can disrupt sleep. Interestingly, the amount of light required to turn down production varies by species with nocturnal animals requiring less light (Reiter, 1991). Dysregulation of melatonin signaling and disrupted sleep have resulted many melatonin supplements on the market today, an industry worth around $2.15 billion in 2022 (Global Market Insights).
According to Dr. Reiter, melatonin has long been recognized as a “regulator of regulators” that could help control the release of other endocrine hormones. When released, melatonin circulates throughout the bloodstream ending up in cells and fluids throughout the body. In amphibia, melatonin causes melanin granules in the skin to retract, thereby controlling skin color by lightening their skin. Its circadian release is also thought to provide clues to organisms about seasonal changes and may therefore help regulate reproductive cycles (Reiter, 1991).
Melatonin is thought to have originated in bacteria where it helped fight oxidative stress (Zhao et al., 2019). In fact, it is known to act as an antioxidant and regulator of circadian rhythm and reproduction in plants as well (Zhao et al., 2019). In more recent years, scientists discovered that melatonin plays numerous roles in animals. Not only does it regulate circadian rhythm and promote sleep, it also helps protect the body from oxidative stress, inflammation, and blood clots in addition to playing roles in blood pressure, metabolism, and immune regulation – and may even help prevent cancer (Masters et al., 2014).
Sources
Reiter RJ. Melatonin: That ubiquitously acting pineal hormone. Physiology. 6(5): 223-227, 1991.
Masters A, Pandi-Perumal SR, Seixas A, Girardin J-L, McFarlane SI. Melatonin, the hormone of darkness: From sleep promotion to Ebola treatment. Brain Disord. Ther. 4(1): 1000151, 2014.
Zhao D, Yu Y, Shen Y, Liu Q, Zhao Z, Sharma R, Reiter RJ. Melatonin synthesis and function: Evolutionary history in animals and plants. Front Endocrinol. 10: 249, 2019.
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Categories: Reproduction and Development, sleep, Time Machine
Tags: American Physiological Society, cancer, Melatonin, physiology
Life Lines by Dr. Dolittle 