Different Expressions of AQP1 and AQP4 in Hyponatremic Rat Brain

The expression of aquaporin-1 (AQP1) in choroid plexus and aquaporin-4 (AQP4) in astrocyte of the hippocampal formation (HF) was studied in the rat to determine the role ofAQP1 and AQP4 in the pathophysiology of systemic hyponatremia (SH). SH was induced by coadministration of dextrose solution intraperitoneally and through subcutaneous implantation of an osmotic minipump containing 8-deamino-arginin vasopressin (50ngiAllh) for 24 and 48 h. Twenty- four and 48 h after the drug administration, there were significant reductions in Na+ concentration (111 +/- 5 and 104 +/- 2 mmol) and serum osmolarity (240 +/- 13 and 221 +/- 14 mOsm/L) as compared with control values (140 +/- 4.7 mmol and 296 +/- 5.2 mOsm/L), (p<0.01). The expression of AQP1 in the choroid plexus was increased three to five times from 24 h to 48 h after SH (329.86 +/- 10.2 4 3/0 and 531.5 +/- 4.4 %. n=4. p<0.01). In contrast, AQP4 expression was significantly decreased up to 48 h after SH (36 +/- 9 %, n=4, p<0.01). Quantitative immunoblotting revealed significant decreases of neuronal proteins in the HF after 24 to 48 h of SH. Therefore, we suggest that altered expression of AQP1 and AQP4 plays important role in the pathogenesis of systemic hyponatremia.

Automated summary

In a rat study, the expression of AQP1 in the choroid plexus and AQP4 in astrocytes of the hippocampal formation was investigated in relation to systemic hyponatremia. The results showed that the expression of AQP1 increased while AQP4 decreased significantly in response to systemic hyponatremia. These changes may play a critical role in the pathogenesis of systemic hyponatremia.