Alterations of Aquaporin-1, 2, 3 Protein Expression in Pregnant Rat Kidney

Cho, Hye Jung; Lee, Chang Bae; Ahn, Kyu Youn

Abstract

The pregnancy causes the marked change in maternal renal hemodynamic and volume homeostasis. During pregnancy, renal sodium and water retention result in an expansion of extracellular fluid and plamsma volume. Although many studies suggested that water balance or water balance disorder was associated with regulation of Aquaporin (AQP) expression, the studies were only limited to AQP-2 expression during the pregnancy. The present study was to examine altered expression and distribution of AQP-1, 2, and 3 proteins in the kidneys of non-pregnant (NP) and pregnant rats using Westhern blot analysis and immunohistochemistry. Pregnant Sprague-Dawley rats were evaluated on various time sets: days 10.5 (P10.5), 12.5 (P12.5), 17.5 (P17.5), and 19.5 (P19.5). In Westhern blot analysis, expression of AQP-1, 2 was peaked at P17.5 and AQP-3 at 19.5. Immunoreactivity of AQP-1 of NP rat was detected in the apical membranes of proximal tubules and thin limb of Henle loop. In pregnant rats, the pattern of cellular labeling of AQP-1 protein was identical to NP rat, but signal intensity was continuously increased from P10.5 and peaked at P17.5. In NP rat, immunoreactivity of AQP-2 was the most prominent in apical region and moderate in cytoplasm of the principal cells of entire collecting duct. In pregnant rats, the pattern of cellular labeling of AQP-2 protein was identical to NP rat, but signal intensity was moderately expressed in P10.5 and P12.5 and most prominent signal was observed in P19.5. In NP rat, immunoreactivity of AQP-3 was most prominent in the bosolateral plasma membrane of principal cells of entire collecting duct. In pregnant rats, the pattern of cellular labeling of AQP-3 protein was identical to NP rat, but signal intensity was continuously increased from P10.5 to P17.5 and peaked at P19.5. These results suggest that the expansion of extracellular fluid volume and water retention are regulated by AQP-1, 2, and 3 during the pregnancy, especially at late stage.