An Overview of Oxytocin: Chemical Structure, Receptors, Physiological Functions, Measurement Techniques of oxytocin, and Metabolism

Abstract

Background: Oxytocin is a peptide hormone comprising 9 amino acids. It is produced in the hypothalamus and stored and secreted by the posterior lobe of the pituitary gland and synthesized in other organs such as the uterus, ovaries, placenta, heart, blood vessels, skin, kidneys, and testis. Receptors of oxytocin are present on myoepithelial cells, heart, blood vessels, macrophages, thymus, pancreas, kidneys, and adipocytes. Objectives: The current review aimed to give highlight the oxytocin structure, receptors, physiological functions, measurement techniques, and metabolism. Oxytocin is a small peptide that consists of nine amino acids in a six–amino acid ring formed by cysteine bonds and a three–amino acid tail with a terminal amine. It is synthesized in brain regions that are critical to behavioral and physiologic homeostasis. Oxytocin is involved in uterine contraction during labor and ejection of milk during breastfeeding and plays a role in social behavior, emotions love and affection, the period after childbirth, and metabolic functions. The action of oxytocin in facilitating human bonding and social relation is well known. The effects of Oxytocin on metabolism and food intake suggesting its potential effects in treating obesity. The half-life time of oxytocin in the brain is triple as long as its half-life time in the periphery. The sensitivity and density of oxytocin receptors increase during labor. After birth, the neonatal baby sucks on his mother's breast, causing the release of milk by stimulating hypothalamic neurons to produce oxytocin. Oxytocin neurons have been heavily implicated in mediating sexual behavior in both humans and animals. The social memory was enhanced by central oxytocin administration in male rats. The action of oxytocin affects social memory in multiple brain regions, including the ventral hippocampus, amygdala, olfactory bulb, and lateral septum. Oxytocin neurons may mediate MC4R-driven sexual behavior in male mice. MC4R signaling in oxytocin neurons permits ejaculation. A decreased latency to ejaculate in rabbits and rats after administration of oxytocin. The effect of oxytocin receptor ligands on the ejaculatory response may be due to the modulation of dopamine serotonin neurotransmission. Oxytocin lowers the threshold for the initiation of maternal behavior but is not involved in its maintenance. The oxytocin and the melanin-concentrating hormone (MCH) systems may interact to modulate maternal behavior. Oxytocin regulates maternal- or mating-regulated mood. Initial measurements of oxytocin by using radioimmunoassay and bioassays suggested that oxytocin concentration in blood is very low, 5 pg/ml, with small increases as pulses,15 pg/ml, during lactation and uterine contractions. Variations in oxytocin concentration, especially in rapid response to specific experiences, such as anticipation of breastfeeding, sexual stimulation, exercise, affiliative social contact, and psychologic stress. Oxytocin is rapidly removed from the plasma by the liver and kidney. Oxytocinase activity increases throughout pregnancy and peaks in the plasma, placenta, and uterus near term. It is also expressed in mammary glands, the heart, the kidney, and the small intestine. Lower levels of activity can be found in the brain, spleen, liver, skeletal muscle, testes, and colon. The plasma half-life of oxytocin ranges from 1 to 6 minutes. The half-life is decreased in late pregnancy and during lactation. Conclusion: It can be concluded that oxytocin is a peptide hormone that is synthesized in brain regions and other organs and posse's receptors in many organs. It plays a role in social behavior, emotions love, and affection, the period after childbirth, and metabolic functions. Its potential effects in treating obesity. The half-life time of oxytocin in the brain is triple as long as its half-life time in the periphery. Oxytocin neurons may mediate MC4R-driven sexual behavior. Variations in oxytocin concentration, especially in rapid response to specific experiences. Oxytocin is rapidly removed from the plasma by the liver and kidney. The plasma half-life of oxytocin ranges from 1-6 minutes. The half-life is decreased in late pregnancy and during lactation.