Age-Related Dysfunction of Water Homeostasis
Dehydration can be an issue in older people. As in every complex system in the body, the mechanisms by which hydration is regulated become dysfunctional with advancing age. Researchers here look at the brain region responsible for regulating some of the response to dehydration, cataloging altered gene expression in search of the more important mechanisms involved in the vulnerability of old people to harmful levels of dehydration.
Ageing is accompanied by an increased prevalence of disorders of body salt and water composition. As revealed by the UK Dehydration Recognition In Our Elders (DRIE), 20% of residents in care are dehydrated. Many elderly patients admitted to the hospital present osmotic balance disorders, and dehydration (DH) is often a cause of morbidity and mortality in senior citizens. Thus, to improve healthy living among the elderly, we need to understand why salt and water imbalances occur in this age group. Both peripheral and central mechanisms controlling salt and water homoeostasis change with age. Ageing is accompanied by a gradual decline in renal function, with urine-concentrating capacities reduced in the elderly compared to younger subjects. This diminished ability to conserve bodily water, accompanied by reduced thirst and insufficient water intake after fluid deprivation, makes the elderly more prone to DH.
Ageing is associated with altered neuroendocrine function. In the context of the hypothalamic supraoptic nucleus (SON), which makes the antidiuretic hormone arginine vasopressin, ageing alters acute responses to hyperosmotic cues, rendering the elderly more susceptible to dehydration. Chronically, vasopressin has been associated with numerous diseases of old age, including type 2 diabetes and metabolic syndrome.
We compared the transcriptomes of the SON in adult and aged euhydrated rats and found massive changes in gene expression associated with ageing, including genes involved in extracellular matrix (ECM) organisation and cell adhesion. It is known that the SON has a complex and dynamic ECM that has been implicated in its physiological functioning. The transcriptomic response to dehydration is overall blunted in aged animals compared to adults, and there is a specific enrichment of differentially expressed genes related to neurodegenerative processes in the aged cohort, suggesting that dehydration itself may provoke degenerative consequences in aged rats.
Dysfunctional water homoeostasis in ageing is associated with the inappropriate release of the antidiuretic hormone arginine vasopressin (AVP). The capabilities of the AVP system to respond to osmotic stress decrease with age. In the aged animal, the capacity of the AVP system to respond to dehydration is attenuated. These deficits may be associated with dysfunction in mechanisms controlling transcription, mRNA stability, or translation. Indeed, we have previously shown that the steady-state response to dehydration of a number of selected gene transcripts is attenuated in aged animals. This appears to be a transcriptome level effect, with many of the common genes regulated by dehydration showing a blunted response in aged animals compared to adults. This generalised attenuation of the transcriptomic response to dehydration is likely to greatly affect SON function and overall osmoregulatory effectiveness.
Complex....? Maybe. Fixable? Sure. Try HRT to have good estrogen levels (yes, males too!), add 2IU HGH/day.
Human growth hormone (HGH), also known as somatotropin, plays a role in regulating water homeostasis through its interaction with several organs and systems in the body. Here's an overview of how HGH influences water balance:
Antidiuretic Hormone (ADH) Release: HGH stimulates the secretion of antidiuretic hormone (ADH) from the posterior pituitary gland. ADH, also called vasopressin, acts on the kidneys, promoting water reabsorption and reducing urine output. This mechanism helps to conserve water and maintain proper hydration levels in the body.
Renal Tubular Absorption: HGH influences the renal tubules' ability to reabsorb water and electrolytes. It enhances the reabsorption of sodium ions, which leads to increased water reabsorption as well. This process helps to retain water within the body and prevent excessive water loss through urine.
Increased Blood Volume: HGH promotes the synthesis and release of insulin-like growth factor 1 (IGF-1) from the liver and other tissues. IGF-1 stimulates red blood cell production in the bone marrow, leading to an increase in blood volume. The expanded blood volume helps to maintain adequate blood pressure and ensures effective transport of nutrients and oxygen throughout the body.
Regulation of Thirst: HGH influences the regulation of thirst, which is an essential mechanism for maintaining water balance. It interacts with the hypothalamus, a region of the brain that controls thirst perception, and can modulate the sensation of thirst. By influencing thirst, HGH indirectly affects water intake and helps regulate fluid balance.
Overall, human growth hormone plays a crucial role in water homeostasis by promoting water reabsorption in the kidneys, increasing blood volume, regulating thirst perception, and maintaining adequate hydration levels in the body.
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Estrogen, a group of hormones primarily produced in the ovaries, also contributes to water homeostasis through various mechanisms. Here's an overview of estrogen's role in regulating water balance:
Renal Water Reabsorption: Estrogen influences the renal tubules' ability to reabsorb water in the kidneys. It enhances the reabsorption of sodium ions, which promotes water retention. This effect helps to prevent excessive water loss through urine and maintain adequate hydration levels.
Antidiuretic Hormone (ADH) Sensitivity: Estrogen increases the sensitivity of the kidneys to the effects of antidiuretic hormone (ADH), also known as vasopressin. ADH acts on the kidneys, promoting water reabsorption and reducing urine output. By enhancing ADH sensitivity, estrogen facilitates water retention and helps prevent excessive urine production.
Fluid Balance during Menstrual Cycle: Estrogen levels fluctuate throughout the menstrual cycle. During the follicular phase (prior to ovulation), estrogen levels rise. This hormonal change affects fluid balance by promoting sodium and water retention. It helps to maintain adequate blood volume and prevent dehydration.
Regulation of Aldosterone: Estrogen can influence the release and activity of aldosterone, a hormone produced by the adrenal glands. Aldosterone plays a crucial role in regulating sodium and water balance. Estrogen can enhance aldosterone synthesis, leading to increased sodium reabsorption and subsequent water retention.
Interaction with Renin-Angiotensin System: Estrogen has been shown to interact with the renin-angiotensin system, which plays a role in regulating blood pressure and fluid balance. It can modulate the production and activity of angiotensin, a hormone involved in controlling blood vessel constriction and sodium reabsorption. By influencing this system, estrogen indirectly affects water balance.
Overall, estrogen contributes to water homeostasis by promoting water reabsorption in the kidneys, enhancing ADH sensitivity, regulating fluid balance during the menstrual cycle, interacting with the renin-angiotensin system, and influencing aldosterone activity. These mechanisms help maintain proper hydration levels in the body.