Introduction:
Vasopressin is a hormone that has a role in fluid balancing and it acts in the kidney to bring about this action. It has the function of maintaining the temperature of the body, blood volume, and in proper excretion of urine from the kidney. This hormone is also called antidiuretic hormone. Apart from these functions, it also plays a role in regulating circadian rhythm.
What Is Circadian Rhythm?
Circadian rhythm means changes in physical, mental, and behavior in 24 hours. Light and dark affect These processes in almost all living beings. The body can keep its circadian rhythm through genes that bind to proteins in the cell’s nucleus. This binding may be more at night and lesser in the daytime. Environmental factors are also responsible for affecting circadian rhythm.
Circadian rhythm may bring changes in the following
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Hormone levels.
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The process of digestion and eating habits.
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The temperature of the body.
Mainly circadian rhythm influences the sleep cycle. The suprachiasmatic nucleus (SCN) is a structure in the hypothalamus, a part of the brain. SCN controls the secretion of a hormone called melatonin. This hormone is considered to be responsible for sleep. SCN gets information from optic nerves regarding the light that enters through the eyes to the brain. At night due to less light, the SCN sends information to the brain to produce more melatonin. Because of increased levels of melatonin, the individual may feel drowsy and goes to sleep.
Factors that can influence circadian rhythms are
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Changes in the genes.
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Shifts during work may affect circadian rhythms.
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Lights of electronic devices may affect circadian rhythms.
What Are the Effects of the Sleep-Wake Cycle?
Sleep may affect and is responsible for causing many health conditions like heart disease, obesity, diabetes, and chronic kidney dysfunction. Studies have suggested that hydration plays a role in physiological functioning and health. When there is a decreased water intake, it may lead to health problems like headaches, fatigue, irritated mood, dry mouth, and visual problems. Sometimes, due to dehydration, death can also occur. Hence giving proper hydration may reduce the risk of urolithiasis (kidney disease) and urinary tract infections. Hydration in the body is regulated by a hormone system called renin-angiotensin-aldosterone. This system helps regulate urine concentration and in conserving the water in the body.
When there is hydration, vasopressin hormone is released as a response. This hormone also has a role in circadian rhythm. Vasopressin levels increase during late sleep periods, to avoid dehydration in the sleep. When there is a disturbance in sleep, vasopressin production will decrease and affect body water balance. During long sleep hours, hydration will be affected due to higher loss of water through respiration, and restriction of water intake for long hours may affect hydration and release of vasopressin. The long and short duration of sleep may affect hydration and other functions like insulin sensitivity, hunger/satiety endocrine signaling system, cardiovascular function, and kidney function.
What Is the Role of Vasopressin in Circadian Rhythm?
Vasopressin is called arginine vasopressin (AVP). It plays as a hormone, and neurotransmitter and in recent years it is identified as a neuromodulator in the brain, especially in the SCN of the hypothalamus.
SCN contains neurons of AVP. Whenever there is a disturbance in the sleep-wake cycle during aging, and due to depression, decreased levels of AVP may be found in SCN. Loss of neurons of AVP in SCN is related to increased activity of fragmentation without loss of amplitude in humans. The signaling of AVP is found to change the SCN period and phase in a specific manner which makes the master clock interacts with downstream tissues and thereby respond to changes in the environment.
A study has shown that AVP neurons are an essential component of circadian pacemaker cells of SCN. This clearly states that AVP has a role in circadian rhythm.
Studies have found that AVP neurons play a role in the functioning of SCN. SCN contains V1A and V1B receptors in it. V1A and V1B are vasopressin receptors that are G protein-coupled receptors and these activate the gaq signaling cascade. V1A signaling helps in increasing intracellular calcium and depolarizes the SCN neurons. These receptors also reset the SCN by activating the gaq cascade. SCN resetting affects the circadian rhythm. Among three receptors, V1A, V1B, and V2, V1A is responsible for the circadian function carried out by AVP.
One of the studies showed circadian variation when there was a change in the levels of AVP in cerebrospinal fluid. This variation was due to AVP in SCN. The biological clock influences the health, cognitive performance, and alertness of an individual. Central pacemaker integrates light information to regulate rhythm in gene expression. These cellular clocks are influenced by neuromodulators. Many neurons are added to act as a single circadian unit at the cellular level. Many neurotransmitters and neuromodulators are responsible for coherent circadian oscillations.
Circadian rhythm can be influenced by light. A small group of cells called retinal ganglion cells (RGCs) project into SCN. These RGCs can release AVP more especially at the end of the night when compared to at the end of the day. When there is a release of light-induced AVP, neurons in SCN increase their response. RGCs increase the expression of genes like c-fos, per-1, and per-2 in SCN. Genes per-1 and per-2areclock genes that are activated by light.
The mammalian clock is dependent on genes and these are associated with neuromodulators. Clock-controlled genes are encoded by three peptides called prokineticin 2, cardiotrophin-like cytokine, and AVP. These peptides are responsible for the action of SCN and its efferent organs. Hence AVP has a role in circadian rhythm.
Neurons of SCN act as circadian oscillators. AVP receptor signaling is important to induce clock genes called cry1, and cry 2 which are responsible for circadian timing in SCN. A study has found stated that coupling between neurons of SCN and neuropeptides is important for the functioning of SCN. AVP is responsible for coupling action and its absence showed to affect the circadian rhythm.
Conclusion:
Circadian rhythm is involved in various functions of the body. It is mainly dependent on SCN. AVP has a role in the function of SCN. Hence AVP may affect the circadian rhythm. This in turn affects many functions of the body. AVP is considered to have a very important role in circadian rhythm and has effects on the sleep-wake cycle.
