Different expressions of AQP1 and AQP4 in hyponatremic rat brain / Diferentes expresiones de AQP1 y AQP4 en cerebro de rata hiponatrémico

SUMMARY: 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 of AQP1 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 (50ng/µl/h) 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 % 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.

RESUMEN: En este análisis se estudió la expresión de acuaporina-1 (AQP1) en plexo coroideo y acuaporina-4 (AQP4) en astrocitos de la formación hipocampal (FH) en ratas para determinar el papel de AQP1 y AQP4 en la fisiopatología de la hiponatremia sistémica (HS). La HS fue inducida mediante la coadministración de solución de dextrosa por vía intraperitoneal y mediante la implantación subcutánea de una minibomba osmótica que contenía vasopresina 8-desaminoarginina (50 ng /µ l / h) durante 24 y 48 h. Veinticuatro y 48 h después de la administración del fármaco, hubo reducciones significativas en la concentración de Na + (111 ± 5 y 104 ± 2 mmol) y la osmolaridad sérica (240 ± 13 y 221 ± 14 mOsm /µL) en comparación con los valores de control (140 ± 4,7 mmol y 296 ± 5,2 mOsm / L), (p <0,01). La expresión de AQP1 en el plexo coroideo se incrementó de tres a cinco veces de 24 a 48 h después de HS (329,86 ± 10,2 % y 531,5 ± 4,4 %, n = 4, p <0,01). Por el contrario, la expresión de AQP4 se redujo significativamente hasta 48 h después de HS (36 ± 9 %, n = 4, p <0,01). La inmunotransferencia cuantitativa reveló disminuciones significativas de proteínas neuronales en el FH después de 24 a 48 h de SH. Por lo tanto, sugerimos que la expresión alterada de AQP1 y AQP4 juega un papel importante en la patogénesis de la hiponatremia sistémica.

Altered Expression of eNOS and VEGF in the Rat Choroid Plexus following Systemic Hyponatremia / 대한해부학회지

In the present study, alterations of the endothelial nitric oxide synthase (eNOS) and the vascular endothelial growth factor (VEGF) expression in the third ventricle choroid plexus and their effects to the adjacent hippocampus were studied in the systemic hyponatremic model with the total of 29 adult male Spraque-Dawley rats. Systemic hyponatremia was induced by the coadministration of 30mL(~12% body weight) dextrose solution (140 mmol/L) intraperitoneally and a 3-microgram subcutaneous dose of 1-deamino-8-D-arginine vasopressin (dDAVP). Two and six hours after the drug administration, there were significant reductions in the serum osmolarity (252+/-5.1 and 252+/-6.4 mOsm /L) and in Na+ concentration (117+/-1.7 and 97.2 mM) from the control values (osmolarity: 296+/-5.2 mOsm/L, Na+ concentration: 140+/-4.7 mM). The expression levels of eNOS and VEGF protein in the choroid plexus were determined by using immunohistochemistry and quantitative immunoblotting. There was a significant increase in the expression of the eNOS (135%+/-2%, P<0.05), whereas the expression of the VEGF was slightly increased compared with the control rats after 2 h of systemic hyponatremia. 6 h after the onset of systemic hyponatremia, expression of the eNOS and the VEGF was decreased simultaneously. Consistent with the expression of the eNOS in choroid plexus after 2 h after systemic hyponatremia, cresyl violet staining revealed necrotic cell death in the hippocampus CA3 subfield, presumably resulting from cerebrospinal fluid (CSF) overproduction and subsequent an elevation of intracranial pressure. Thus, activation of the eNOS protein in the choroid plexus may be one of the molecular mechanisms of the hippocampal cell injury. Additionally, substantial decrease of eNOS and VEGF expression in the choroid plexus after 6 h of the systemic hyponatremia may reflect the eNOS and VEGF in response to the systemic hyponatremia undergo the regulatory changes to prevent the overproduction of CSF. Overall, these results suggest that NO-mediated excessive water influx into the ventricle is important for the cerebral pathogenesis after the systemic hyponatremia.

Altered Expression of Aquaporin 4 (AQP4) in Hippocampal Formation after Systemic Hyponatremia / 대한해부학회지

The expression of aquaporin-4 (AQP4) protein, bi-directional water channel, in the blood-brain barrier of the hippocampal formation (HF) was studied in the rat to determine the role of AQP4 in the pathophysiology of systemic hyponatremia. Systemic hyponatremia was induced by coadministration of 30 ml (~12% body weight) dextrose solution (140 mM) intraperitoneally and a 3-microg subcutaneous dose of 1-deamino-8-D-arginine vasopressin (dDAVP). Two and six hours after the drug administration, there were significant reductions in the serum osmolarity (252+/-5.1 and 252+/-6.4 mOsm/L) and in Na+/- concentration (117+/-1.7 and 97.2 mM) from the control values (296+/-5.2 mOsm/L, 140+/-4.7 mM). Brain injury in the HF and the expression of AQP4 were determined by using TUNEL, immunohistochemistry and quantitative immunoblotting. TUNEL revealed apoptotic cell death in the dentate gyrus (DG), presumably resulting from brain edema and a subsequent elevation of intracranial pressure after 2 h of systemic hyponatremia. However, AQP4 expression was decreased by 82%+/-6% after 2 h of systemic hyponatremia and then normalized after 6 h (108%+/-9%) compared with that of the control. Therefore, apoptotic cell death in the DG from brain swelling in this systemic hyponatremic model is likely associated with decrease of excessive brain water elimination because reincreased AQP4 expression/function accelerates the elimination of apoptotic cells from the DG.