Abstract P268: The Effects of a Slow Pressor Dose of Angiotensin II on Sodium Transporters Expression in the Kidney Cortex are Independent of PPAR-alpha

Abstract

A slow pressor dose of Angiotensin II (Ang II) has been shown to increase the expression of sodium transporters in the proximal tubules (NHE3), TALH (NKCC2) and distal nephrons (NCC) of Sprague Dawley rats before an increase in blood pressure. Peroxisome Proliferator Activated Receptor - alpha (PPAR-alpha) has been shown to be involved in pressure natriuresis through changes in sodium transport via ameloride and thiazide-dependent mechanisms. We hypothesized that the changes in expression of the sodium transporters during Ang II hypertension were dependent upon PPAR-alpha expression. To address this hypothesis, we treated wild-type (WT) and PPAR-alpha knockout (KO) mice with a slow pressor dose of Ang II (400 ng/kg/min) for 12 days. Mean arterial pressure (MAP) was measured by radiotelemetry. Control MAP was not different between WT (110 ± 8 mmHg) and PPAR-alpha KO mice (112 ± 12 mmHg). On day 12 of Ang II, MAP for PPAR-alpha KO (156 ± 16) mice was significantly higher than WT (138 ± 11 mmHg) mice. The expression of NHE3, NHERF1, NKA-α1 subunit, NKCC2, and NCC was detected in kidney cortical homogenates by western blotting. Kidneys were homogenized and 25 μg of supernatant proteins were separated by 10% SDS-PAGE, transferred to nitrocellulose paper, and blotted against antibodies to NHE3, NHERF1, NKA α1 subunit, NKCC2, and NCC. The slow pressor dose of Ang II decreased the expression of NHE3 in WT + Ang II (0.14 ± 0.02 ODU) and PPAR-alpha KO + Ang II (0.10 ± 0.02 ODU), when compared to WT (2.61 ± 0.93 ODU) and PPAR-alpha KO (2.20 ± 0.58 ODU) controls. Ang II-treatment also decreased NKCC2 in both WT (0.31 ± 0.10 ODU) and PPAR-alpha KO (0.22 ± 0.03 ODU). Ang II hypertension caused similar decreases in NCC and NHERF1 expression in WT and PPAR-α KO mice. NKA alpha1 subunit expression was increased during Ang II hypertension in both WT (1.06 ± 0.26 ODU) and PPAR-α KO (1.64 ± 0.26 ODU) mice. Our results suggest that the effects of a slow pressor dose of Ang II on expression of sodium transporters are independent of PPAR-alpha expression. Future studies are needed to determine the effects of decreasing NHE3, NKCC2, NCC and NHERF1 expression in the kidney on urinary salt excretion during a slow pressor dose of Ang II.