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Hyponatremia in pregnancy
Published in Nadia Barghouthi, Jessica Perini, Endocrine Diseases in Pregnancy and the Postpartum Period, 2021
Anthony Parravani, Bethany Pellegrino
Nonpregnant state, maintenance of serum osmolality and sodium:Under nonpregnant conditions, serum osmolality is maintained within a narrow range of 275–295 mOsm/L.Any changes in serum osmolality are sensed by osmoreceptors which respond to correct the change.An increase in serum osmolality by 1–2% results in the release of ADH from the posterior pituitary, which acts on the Arginine Vasopressin Receptor 2 (AVPR2) on the basolateral membrane of the collecting ducts in the kidneys. This leads to the upregulation of aquaporin 2 channels and increased water absorption by the kidneys.Any increase in serum osmolality also stimulates the thirst center in the hypothalamus, resulting in water intake to assist in correction of the hypertonic state.4
History of Asphyxia-related Deaths
Published in Burkhard Madea, Asphyxiation, Suffocation,and Neck Pressure Deaths, 2020
The working group of Kondo (see also Chapter 15) investigated the suitability of the expression of aquaporin-3 and aquaporin-1 as vitality markers of strangulation marks (Ishida et al. 2018). Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells. They are expressed in many epithelia and endothelia that can regulate osmolality throughout the body. Aquaporin-1 is expressed in vascular endothelial cells throughout the body, including the skin. Epidermal aquaporin-3 is increased in a cutaneous burn wound. A total of 24 neck compression marks by ligatures were investigated. After immunostaining, a total of ten high power fields were selected randomly. Antemortem neck compression enhanced aquaporin-3 expression in the keratinocytes. These results have been confirmed by this author's own working group (Figure 1.40). Aquaporin-3 might be useful as a marker of all kinds of antemortem skin injuries.
Water and sodium
Published in Martin Andrew Crook, Clinical Biochemistry & Metabolic Medicine, 2013
Antidiuretic hormone, by regulating aquaporin 2, enhances water reabsorption in excess of solute from the collecting ducts of the kidney and so dilutes the extracellular osmolality. Aquaporins are cell membrane proteins acting as water channels that regulate water flow. When ADH secretion is a response to a high extracellular osmolality with the danger of cell dehydration, this is an appropriate response. However, if its secretion is in response to a low circulating volume alone, it is inappropriate to the osmolality. The retained water is then distributed throughout the TBW space, entering cells along the osmotic gradient; the correction of extracellular depletion with water alone is thus relatively inefficient in correcting hypovolaemia. Plasma osmolality normally varies by less than 1–2 per cent, despite great variation in water intake, which is largely due to the action of ADH.
Submandibular gland epithelial development and the importance of junctions
Published in Tissue Barriers, 2022
Hélène Bonnet, Carlos Agustin Isidro Alonso, Indra R. Gupta
Although there are at least 5 water aquaporin water channels expressed in the salivary gland, Aquaporin-5 is the major channel expressed in the apical membrane of acinar cells. Aqp5-KO mice have a decrease in saliva production secondary to the loss of transcellular water transport that results in the formation of a hypertonic saliva.10 In addition to their defect in transcellular water transport, Aqp5-KO mice exhibit a 2-fold decrease in paracellular permeability as shown by a decrease in the transport of a 4 kDa dextran. The decrease in paracellular permeability is associated with decreased expression of several tight junction proteins including claudin-3, claudin-7 and occludin in female Aqp5-KO mice. Similar observations were made in male knockout mice although the effect was only statistically significant for claudin-7 and occludin. This suggests there is a concurrent defect in paracellular water transport in the absence of Aquaporin-5 that is poorly understood.11 Taken together, the permeability of the epithelial barrier within the salivary gland is integral to the formation of saliva and the maintenance of its composition.
Carbonic anhydrase 12 mutation modulates membrane stability and volume regulation of aquaporin 5
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Soyoung Hwang, Jung Yun Kang, Min Jae Kim, Dong Min Shin, Jeong Hee Hong
Aquaporin 5 (AQP5) is a member of the transmembrane protein channels involved in transcellular water permeability and a dominant water channel in the epithelia of the salivary and lacrimal glands and the lung alveoli1,2. A study using AQP5 knockout mice showed that AQP5 plays a central role in salivary secretion3. Indeed, AQP5 classically prevents excessive water reabsorption and modulates cell shape and volume4. Recently, several new roles of AQP5, in addition to water transport, have been discussed. AQP5 is involved in migration by activating Ras and Rac signalling in cancer cells5 and is associated with cancer cell invasion and tumour metastasis through the NF-κB signalling pathway6. Additionally, hyperosmotic stress-mediated AQP5 expression mediates the expression of inflammatory cytokines and cell death through the JNK1/2 MAPK signalling pathway7.
Desmopressin and nocturnal voiding dysfunction: Clinical evidence and safety profile in the treatment of nocturia
Published in Expert Opinion on Pharmacotherapy, 2018
Desmopressin’s antidiuretic action (DOA) increases water reabsorption in the renal collecting ducts and the ascending limb of Henle’s loop, reducing urine volume and increasing urine osmolality. At the cellular level, this effect is manifested through V2 receptor-mediated elevation of intracellular adenylate cyclase [29]. The translocation of aquaporin channels associated with cytosolic vesicles to the apical/luminal membrane of collecting duct cells allows for free water to passively be reabsorbed from the nephron back into systemic circulation. The antidiuretic effects of desmopressin, which are 4000-fold greater than the drug’s vasodilating action, are long sustained [30]. After oral administration, the duration of effect of 6–14 h is to be expected. The antidiuretic effects are 3–10-fold greater than vasopressin [31]. When given orally, the drug’s bioavailability is reduced by the presence of a variety of enzymes to approximately 0.1% of that of subcutaneous injection [22]. Published literature showed that desmopressin administered as crushed or chewed tablets, or as an oral solution, has the same net effect on decreasing urine volume and increasing urine osmolality as swallowing tablets whole [32].