Acute Normovolemic Hemodilution Changes the Aquaporin Expression Profile in Specific Tissues and Induces Apoptotic and Inflammatory Processes in a Rat Model

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Background and Objectives: Acute normovolemic hemodilution (ANH) is commonly used to minimize perioperative blood loss and transfusion requirements. While it is considered safe, the molecular effects of ANH on vital organs remain unclear. Aquaporins (AQPs), the principal cellular water transporters, may play a role in tissue adaptation or injury under hemodilution stress. This study aimed to evaluate the impact of ANH on AQP1, AQP3, and AQP4 expression profiles and their association with apoptotic and inflammatory markers in the aorta, heart, kidney, and liver. Materials and Methods: Male Hannover–Sprague Dawley rats (6 months old) were assigned to control (no procedure), sham (anesthesia only), and hemodilution (anesthesia and ANH) groups. ANH was induced using balanced crystalloid infusion. Physiological parameters, blood gases, electrolytes, and metabolic profiles were monitored. At 24 h post-ANH, tissues were harvested for immunoblot analysis of AQPs, as well as apoptotic and inflammatory markers. Results: At 24 h post-ANH, changes in potassium, calcium, and glucose levels, decreased hematocrit, increased lactate, decreased pH, base excess, and PaCO2 were detected, indicating mild metabolic acidosis due to tissue hypoxia and impaired oxygen delivery. Apoptotic and inflammatory responses were observed across all tissues, but AQP alterations were organ-specific. In the heart, AQP1 downregulation correlated inversely with NF-κB and TNF-α levels, while AQP3 upregulation positively correlated with apoptosis. The aorta showed the opposite pattern. In the kidney, AQP4 downregulation was strongly associated with apoptosis and inflammation. Furthermore, ANH selectively increased the AQP3 expression without affecting AQP1 or AQP4 in the liver. Conclusion: ANH induces differential aquaporin expression patterns in major organs, with tissue-specific associations with apoptosis and inflammation. These findings highlight a potential mechanistic role for AQPs, particularly AQP1 and AQP3, in modulating tissue response to hemodilution. These molecular adaptations may serve as early indicators of tissue stress, suggesting clinical relevance for perioperative fluid strategies.