Nitric oxide: a hormone, a hormonal regulator, a neurotransmitter, or a neuromodulator
DOI:
https://doi.org/10.71112/qdhmne84Keywords:
nitric oxide, hormone, neurotransmitter, neuromodulator, homeostasisAbstract
Nitric oxide (NO) is a simple gaseous molecule composed of one nitrogen atom and one oxygen atom, whose discovery earned the 1998 Nobel Prize in Physiology or Medicine. As a highly reactive, freely diffusible free radical, NO is continuously synthesized through an enzymatic pathway (from L-arginine via nitric oxide synthases) and a non-enzymatic pathway (reduction of dietary nitrates). This narrative review examines the evidence supporting the multiple biological roles of NO, arguing that the molecule simultaneously functions as a hormone, a hormonal regulator, a neurotransmitter, and a neuromodulator. Its effects on blood circulation, inflammation, glucose and lipid metabolism, the hypothalamic-pituitary axis, joint function, and neurotransmission and neuroplasticity within the central nervous system are described. The pathological consequences of NO imbalance—including diabetes, insulin resistance, osteoarthritis, rheumatoid arthritis, and neurodegenerative diseases such as Alzheimer's and Parkinson's disease—are also discussed, alongside lifestyle habits that support its natural synthesis, given that NO production declines with age. The article concludes by proposing that Endocrinology and Neurology formally incorporate NO into their respective conceptual frameworks, given the breadth and significance of its physiological functions.
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