Abstract 671: Regulation of renal NADPH oxidase and inflammation by Dopamine D2 receptors
An intact dopaminergic system is necessary to maintain normal blood pressure (BP). Alterations in D2-like receptor function have been reported in hypertension. In humans, polymorphisms of the dopamine D2 receptor (D2R) gene are associated with a reduction of D2R density, elevated BP, and essential hypertension. We have previously reported that disruption of the D2R in mice (D2−/ −) results in elevated BP, increased aldosterone production, and increased oxidative stress evidenced by increased excretion of 8-isoprostane, and renal NADPH oxidase activity, and expression of Nox1, Nox2 and Nox4. We hypothesized that increased oxidative stress in D2−/ − could result in tissue inflammation. To test this hypothesis we quantified the mRNA expression of inflammation-related mediators and markers by RT-PCR. We found increased renal expressions of TNFα(131 ± 9 vs 100 ± 9, P<0.05, n=5/ each group) and VCAM (136 ± 4 vs 100 ± 2, P<0.05) in D2−/ − mice relative to D2+/+littermates (values set at 100%). The expressions of PPARγ(79 ± 2 vs 100 ± 6, P<0.05), TGFβ(80 ± 6 vs 100 ± 7, P<0.05) and VEGF receptor 2 (77 ± 2 vs 100 ± 2, P<0.05) were decreased in D2−/ − kidneys while the expression of VEGFα was similar in the two mouse strains. The effects on TNFα and VEGF receptor 2 were independent of aldosterone because they were observed in kidneys of D2+/− mice which were hypertensive (D2+/−: 126 ± 4; D2+/+: 92 ± 3 mmHg, P<0.03) and had increased excretion of 8-isoprostane but did not have increased aldosterone excretion. To further determine the role of D2R in the increased renal oxidative stress, we treated mouse renal proximal tubule cells in culture for 24 h with quinpirole (1μM), a D2R/D3R agonist. The treatment decreased the protein expressions of Nox1, Nox2 and Nox 4 by 15 ± 2, 16 ± 3 and 12 ± 1% respectively (P<0.05; n = 6 per group) and the activity of NADPH oxidase by 15 ± 1% (P<0.05). The effect of quinpirole was completely abolished by a D2R antagonist (L- 741,262;1μM/ 24 h), but not by a D3R antagonist. (GR103,691;1μM/ 24 h) and therefore the effects were mediated by the D2R. Our results show that decreased D2R function, by direct and indirect mechanisms, may not only result in increased oxidative stress and hypertension but also in renal inflammation.