Abstract 089: Dopamine D 2 Receptor is Associated with Inverse Salt Sensitivity

Abstract

Our previous studies of salt sensitivity of blood pressure have demonstrated that approximately 11% of study participants have a paradoxical increase in blood pressure (> or = to 7-mm Hg) on a low NaCl diet (defined as inverse salt sensitivity (ISS)). However the mechanisms responsible for this effect are not known. We demonstrated that single nucleotide polymorphisms (SNPs) in the dopamine type 2 receptor (D 2 R) (RS6276 and 6267) are highly associated with ISS ( P values of 1.0х10 –2 and 3.8х10 –2 with odds ratios of 0.32 and 0.48 in unadjusted regression models, respectively). The C allele at both sites confers protection. The D 2 R is strongly expressed throughout the cytoplasm of proximal tubule cells in human kidney tissue slices. We also cultured RPTC from the urine from 4 salt resistant (SR) and 3 ISS participants enrolled in our clinical salt sensitivity studies. We hypothesize that D 2 R containing SNPs have altered receptor expression, and altered signaling compared to wild type controls. ISS participants were homozygous variant for the two D 2 R alleles and showed more D 2 R expression than SR RPTC heterozygous variant (HV) for the two alleles (ISS: 1.166±0.059 n=3 vs SR: 0.969±0.024 n=4, P<0.05, t-test). D 2 R expression was increased when the ISS cells were stimulated by a non-selective D 2 R agonist bromocriptine to a greater extent in the D 2 R SNP cell lines (ISS: VEH 1.166±0.059, vs bromocriptine 1.474 ± 0.040, n=3, P<0.05, t-test). Using the ROS reagent assay, dihydroethidium, there was found to be more ROS products in ISS cells than SR cells when stimulated under low salt (ISS: 1.145 ± 0.053, n=3 vs SR: 0.722 ± 0.101, n=4, P<0.05, t-test). We used a highly selective D 2 R agonist (sumanirole) to stimulate wild-type and SNPed cells, and the results demonstrated no effect in the cells with wild type D 2 R but an increase in ROS in cells heterozygous for the D 2 R SNPs (SNP: VEH 38,364±1,266, sumanirole 50,926 ± 3,310, VS WT: VEH 34,562±1,831 sumanirole 34,435 ± 1,614 RFU n=12, P<0.05, t-test) consistent with the higher expression of D 2 R found in ISS urine cells. We hypothesize that SNPs in the D 2 R lead to increased reactive oxygen species which has previously been associated with renal fibrosis and hypertension.