Dr. Srijit Das
Dr. Halima bint Mohammed Al-Balushi
Department of Human and Clinical Anatomy, College of Medicine and Health Sciences
The pineal gland in the brain is the primary source of melatonin (N-acetyl-5-methoxytryptamine), an endogenous hormone released in response to darkness. Melatonin acts on the hypothalamus in the brain. Its release is governed by a tiny region in the brain called the suprachiasmatic nucleus, which detects light signals from the eyes and instructs the pineal gland to produce more melatonin in darkness and less in light.
Melatonin is well known for its role in controlling sleep-wake cycles and circadian rhythms. This hormone possesses antioxidant, anti-inflammatory, immunomodulatory, and cardioprotective properties. It modulates the seasonal physiological mood changes including the mood changes. Recently, research on melatonin has gained much interest.
Owing to its high metabolic requirements and significant oxidative activity, the human heart is sensitive to damage from various ischaemic insults, inflammation, and reactive oxygen species (ROS). ROS overproduction is linked to heart failure, atherosclerosis, myocardial damage, and endothelial dysfunction.
It has been observed that a disproportionate amount of myocardial infarctions occur in the early morning when melatonin secretion is minimal. When we wake up in the morning, blood pressure and stress hormones tend to spike. This has a detrimental effect on the cardiovascular system.
Melatonin may improve cardiovascular health through various molecular and cellular processes. It acts directly on free radicals and enhances the activity of various antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase. This hormone enhances adenosine triphosphate synthesis, reduces lipid peroxidation, and maintains mitochondrial integrity. Altogether, these protective activities help preserve cellular viability and cardiac function.
When treating acute myocardial infarction, myocardial ischaemia-reperfusion damage is still a major challenge. Restoration of adequate blood flow to the myocardium is necessary to limit myocardial injury. There are various mechanisms through which melatonin attenuates ischaemia-reperfusion injury. Melatonin helps protect blood vessels by neutralizing harmful nitrogen-based compounds that build up during reperfusion. Moreover, it supports the healthy function of the cells lining the blood vessel walls.
Melatonin regulates neutrophil recruitment into the damaged heart tissue and reduces the inflammatory cytokines, especially tumour necrosis factor-alpha, interleukin-1 beta, and interleukin-6. Interestingly, research studies have revealed that administration of melatonin at night may lower blood pressure. Hence, administration of melatonin can be beneficial for cardiovascular conditions, especially myocardial infarction. By lowering stress-related neurohormonal activation, better sleep quality has been linked to melatonin administration, which may also indirectly improve cardiovascular health.
When we travel to distant places that have different time zones, our body’s internal clock is disturbed. This is commonly referred to as ‘jet lag.’ We need to reset our internal clock. In such conditions, consumption of exogenous melatonin may be beneficial because it can help our circadian rhythm to align with the new time zone.
In the field of cardiovascular chronobiology, further research is needed on melatonin and its effects. Studies involving night shift workers and individuals with sleep disorders may provide valuable information.