deamino-arginine-vasopressin and Hypokalemia

It has been reported that several proteins [heat shock protein 70 (Hsp70 and Hsc70), annexin II, and tropomyosin 5b] interact with the Ser(256) residue on the COOH terminus of aquaporin-2 (AQP2), where vasopressin-induced phosphorylation occurs for mediating AQP2 trafficking. However, it remains unknown whether these proteins, particularly Hsp70, play a role in AQP2 trafficking. Semiquantitative immunoblotting revealed that renal expression of AQP2 and Hsp70 was significantly increased in water-restricted or dDAVP-infused rats. In silico analysis of the 5'-flanking regions of AQP2, Hsp70-1, and Hsp70-2 genes revealed that transcriptional regulator binding elements associated with cAMP response were identified at both the Hsp70-1 and Hsp70-2 promoter regions, in addition to AQP2. Luciferase reporter assay demonstrated the significant increase of luminescence after dDAVP stimulation (10(-8) M, 6 h) in the LLC-PK1 cells transfected with luciferase vector containing 1 kb of the 5'-flanking region of Hsp70-2 gene. Hsp70-2 protein expression was also increased in mpkCCDc14 cells treated by dDAVP in a concentration-dependent manner. Cell surface biotinylation analysis demonstrated that forskolin (10(-5) M, 15 min)-induced AQP2 targeting to the apical plasma membrane was significantly attenuated in the mpkCCDc14 cells with Hsp70-2 knockdown. Moreover, forskolin-induced AQP2 phosphorylation (Ser(256)) was not significantly induced in the mpkCCDc14 cells with Hsp70-2 knockdown. In contrast, Hsp70-2 knockdown did not affect the dDAVP-induced AQP2 abundance. In addition, siRNA-directed knockdown of Hsp70 significantly decreased cell viability. The results suggest that Hsp70 is likely to play a role in AQP2 trafficking to the apical plasma membrane, partly through affecting AQP2 phosphorylation at Ser(256) and cell viability.

Topics: Animals; Aquaporin 2; Binding Sites; Cell Membrane; Cells, Cultured; Deamino Arginine Vasopressin; HSP70 Heat-Shock Proteins; Hypokalemia; Kidney Tubules, Collecting; Male; Osmolar Concentration; Phosphorylation; Protein Transport; Rats; Urination; Water Deprivation

The purpose of the present studies was to determine the effects of high-dose aldosterone and dDAVP treatment on renal aquaporin-2 (AQP2) regulation and urinary concentration. Rats were treated for 6 days with either vehicle (CON; n = 8), dDAVP (0.5 ng/h, dDAVP, n = 10), aldosterone (Aldo, 150 microg/day, n = 10) or combined dDAVP and aldosterone treatment (dDAVP+Aldo, n = 10) and had free access to water with a fixed food intake. Aldosterone treatment induced hypokalemia, decreased urine osmolality, and increased the urine volume and water intake in ALDO compared with CON and dDAVP+Aldo compared with dDAVP. Immunohistochemistry and semiquantitative laser confocal microscopy revealed a distinct increase in basolateral domain AQP2 labeling in cortical collecting duct (CCD) principal cells and a reduction in apical domain labeling in Aldo compared with CON rats. Given the presence of hypokalemia in aldosterone-treated rats, we studied dietary-induced hypokalemia in rats, which also reduced apical AQP2 expression in the CCD but did not induce any increase in basolateral AQP2 expression in the CCD as observed with aldosterone treatment. The aldosterone-induced basolateral AQP2 expression in the CCD was thus independent of hypokalemia but was dependent on the presence of sodium and aldosterone. This redistribution was clearly blocked by mineralocorticoid receptor blockade. The increased basolateral expression of AQP2 induced by aldosterone may play a significant role in water metabolism in conditions with increased sodium reabsorption in the CCD.

Topics: Aldosterone; Angiotensin II; Animals; Aquaporin 2; Deamino Arginine Vasopressin; Drinking; Eating; Homeostasis; Hypokalemia; Immunoblotting; Immunohistochemistry; Kidney Cortex; Kidney Tubules, Collecting; Male; Microscopy, Immunoelectron; Phosphorylation; Potassium Deficiency; Rats; Rats, Sprague-Dawley; Rats, Wistar; Renal Agents; Serine; Subcellular Fractions; Water

Ectopic ACTH syndrome (EAS) occurs in about 5-10% of all patients with ACTH-dependent hypercortisolism with most of them caused by intrathoracic neoplasms. It may be associated with overt malignancies or with occult and indolent tumors. We assessed the accuracy of dynamic tests, inferior petrosal sinus sampling (IPSS) using desmopressin, and imaging in the work-up diagnosis of EAS.. Tumor markers, imaging, and outcome data from 25 patients (13F/12M) aged 18-72 years. High dexamethasone suppression test (HDDST), desmopressin test, GHRP-6 test, corticotropin-releasing hormone (CRH) test, IPSS, computed tomography (CT), magnetic resonance imaging (MRI), and (111)In-pentetreotide scintigraphy were revised.. In 5 out of 20 patients HDDST was positive. In 13 patients who underwent desmopressin test, ACTH- and cortisol-positive responses were seen in six and five patients respectively. GHRP-6 test was positive in two out of three cases. Two patients underwent CRH test with negative response. In the seven patients submitted to IPSS using desmopressin in six of them, none had ACTH gradients. CT was positive in 15 out of 21 patients and MRI in 8 out of 17 cases. (111)In-pentetreotide scintigraphy was positive in three out of five patients. Fourteen patients had intrathoracic tumors, five had pheochromocytomas, three had pancreatic tumors, one had a glomic tumor, and had three occult tumors. Six out of 11 patients with metastasis died and 3 others without metastasis died.. IPSS with desmopressin was helpful for differential diagnosis. Patients initially harboring occult carcinoids may also exhibit severe hypercortisolism and those harboring tymic carcinoids had poor prognoses when compared with bronchial carcinoids and pheocromocytomas.

Topics: ACTH Syndrome, Ectopic; ACTH-Secreting Pituitary Adenoma; Adolescent; Adult; Aged; Corticotropin-Releasing Hormone; Deamino Arginine Vasopressin; Dexamethasone; Female; Humans; Hypokalemia; Male; Middle Aged; Oligopeptides; Pituitary Function Tests; Treatment Outcome