SIADHfinal - SIADH SIADH Alexander Usorov, MD July 31, 2007...

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SIADH SIADH Alexander Usorov, MD Alexander Usorov, MD July 31, 2007 July 31, 2007
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SIADH SIADH Most frequent cause of hyponatremia First described by Schwartz et al in 1957 in 2 pts with bronchogenic carcinoma Arginine vasopressin was then identified
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ADH ADH Synthesized in hypothalamus Transported down to posterior pituitary Released in response to hyperosmolality (major stimuli, mediated through osmoreceptors in hypothalamus) or hypovolemia (via baroreceptors in left atrium, aortic arch, etc)
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ADH ADH Binds to V2 receptors in collecting tubules stimulates cyclic adenosine monophosphate leads to insertion of aquaporin-2 channels into apical membranes The goal is to facilitate the transport of solute-free water
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Figure Freeze-fracture appearance of vasopressin-induced intramembrane particle (IMP) aggregates in toad urinary bladder ( A ), toad epidermis ( B ), and rat kidney collecting duct ( C ). The morphology of the aggregates is different in all three vasopressin target cells. In the bladder, the aggregates are tightly packed linear arrays, in the skin they form orthogonally packed square arrays, and in the collecting duct principal cell they form loose clusters that are often located in shallow depressions on the cell surface. Bar = 0.25 µm.
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Figure Aquaporin-2 (AQP2) is internalized by clathrin-coated pits. A and B, Immunogold labeling of AQP2 in clathrin-coated pits (arrows) at the apical plasma membrane of collecting duct principal cells. An antibody against an external epitope of AQP2 was used. C and D, Label-fracture images of LLC-PK1 cells expressing AQP2. Immunogold label for AQP2 is located in intramembrane particle (IMP) clusters on the membrane ( C, arrows ; and is associated with membrane invaginations that resemble clathrin-coated pits ( D, arrows ). For more details, see Sun TX, et al. Bars = 0.25 µm.
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SIADHfinal - SIADH SIADH Alexander Usorov, MD July 31, 2007...

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