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Expression of aquaporin-2 in the collecting duct and responses to tolvaptan. CEN Case Rep 2020; 10:69-73. [PMID: 32779125 DOI: 10.1007/s13730-020-00518-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Accepted: 07/29/2020] [Indexed: 10/23/2022] Open
Abstract
Tolvaptan, a vasopressin type-2 receptor antagonist, is indicated for fluid retention. It is considered that the response to tolvaptan reduces as renal function deteriorates, whereas we sometimes experience "non-responders" to tolvaptan despite well-preserved renal function. While the expression of aquaporin-2 might be a key to response to tolvaptan, detailed mechanism of refractoriness to tolvaptan remains unknown. We experienced two patients with congestive heart failure and diabetic nephropathy, in whom the responses to tolvaptan were uniquely opposite. In one case, immunohistochemical staining showed expression of aquaporin-2 in the collecting duct despite severely reduced renal function, followed by the good response to tolvaptan with increased urine output. In another case, immunohistochemical staining showed absence of aquaporin-2 with infiltration of inflammatory cells in the kidney medulla despite relatively preserved renal function, followed by refractoriness to tolvaptan without any increase in urine output. Inactivated aquaporin-2 expression in the collecting duct, which was for example caused by pre-clinical urinary infection as our latter case, might have an association with refractoriness to tolvaptan.
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Aquaporins in Renal Diseases. Int J Mol Sci 2019; 20:ijms20020366. [PMID: 30654539 PMCID: PMC6359174 DOI: 10.3390/ijms20020366] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2018] [Revised: 01/11/2019] [Accepted: 01/14/2019] [Indexed: 12/16/2022] Open
Abstract
Aquaporins (AQPs) are a family of highly selective transmembrane channels that mainly transport water across the cell and some facilitate low-molecular-weight solutes. Eight AQPs, including AQP1, AQP2, AQP3, AQP4, AQP5, AQP6, AQP7, and AQP11, are expressed in different segments and various cells in the kidney to maintain normal urine concentration function. AQP2 is critical in regulating urine concentrating ability. The expression and function of AQP2 are regulated by a series of transcriptional factors and post-transcriptional phosphorylation, ubiquitination, and glycosylation. Mutation or functional deficiency of AQP2 leads to severe nephrogenic diabetes insipidus. Studies with animal models show AQPs are related to acute kidney injury and various chronic kidney diseases, such as diabetic nephropathy, polycystic kidney disease, and renal cell carcinoma. Experimental data suggest ideal prospects for AQPs as biomarkers and therapeutic targets in clinic. This review article mainly focuses on recent advances in studying AQPs in renal diseases.
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Kato TS, Nakamura H, Murata M, Kuroda K, Suzuki H, Yokoyama Y, Shimada A, Matsushita S, Yamamoto T, Amano A. The effect of tolvaptan on renal excretion of electrolytes and urea nitrogen in patients undergoing coronary artery bypass surgery. BMC Cardiovasc Disord 2016; 16:181. [PMID: 27624603 PMCID: PMC5022266 DOI: 10.1186/s12872-016-0341-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 07/30/2016] [Indexed: 12/02/2022] Open
Abstract
Background Adequate fluid management is an important component of patient care following cardiac surgery. Our aim in this study was to determine the benefits of tolvaptan, an oral selective vasopressin-2 receptor antagonist that causes electrolyte-free water diuresis, in postoperative fluid management. We prospectively examined the effect of tolvaptan on renal excretion of electrolytes and urea nitrogen in cardiac surgery patients. Methods Patients undergoing coronary artery bypass surgery were randomized to receive conventional loop diuretics (Group C, n = 30) or conventional loop diuretic therapy plus tolvaptan (Group T, n = 27). Fractional excretions of sodium (FENA), potassium (FEK) and urea nitrogen (FEUN) were measured in both groups during post-surgical hospitalization. Results Urine output was greater with tolvaptan (Group T) than without it (Group C), and some patients in Group C required intravenous as well as oral loop diuretics. Serum sodium concentrations decreased after surgery in Group C, but were unchanged in Group T (postoperative day [POD] 3, 139.8 ± 3.5 vs. 142.3 ± 2.6 mEq/L, p = 0.006). However, postoperative FENA values in Group C did not decrease, and the values were similar in both groups. Serum potassium levels remained lower and FEK values remained higher than the preoperative values, but only in Group C (all p < 0.05). BUN increased postoperatively in both groups, but it remained higher than its preoperative value only in Group C (all p < 0.01). Group T showed an initial increase in BUN, which peaked and then returned to its preoperative value within a week. The FEUN increased postoperatively in both groups, but the change was more pronounced in Group T (POD7, 52.7 ± 9.3 vs. 58.2 ± 6.5 %, p = 0.025). Conclusions Renal excretion of sodium and potassium reflects the changes in serum concentration in patients treated with tolvaptan. Patients treated only with loop diuretics showed a continuous excretion of sodium and potassium that led to electrolyte imbalance, whereas the combination of loop diuretics and tolvaptan increased renal urea nitrogen elimination. Tolvaptan therefore appears to be an effective diuretic that minimally affects serum electrolytes while adequately promoting the elimination of urea nitrogen from the kidneys in patients undergoing coronary artery bypass surgery. Trial registration The present study is registered with the UMIN Clinical Trials Registry (ID: UMIN000011039)
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Affiliation(s)
- Tomoko S Kato
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan.
| | - Hiroshi Nakamura
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Mai Murata
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Kishio Kuroda
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Hitoshi Suzuki
- Division of Nephrology, Department of Internal Medicine, Juntendo University School of Medicine, Bunkyo-ku, Tokyo, Japan
| | - Yasutaka Yokoyama
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Akie Shimada
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Satoshi Matsushita
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Taira Yamamoto
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Atsushi Amano
- Department of Cardiovascular Surgery, Heart Center, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan
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