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Defective dopamine D1A dopamine receptor/ G-protein coupling has been demonstrated in renal proximal tubules of the spontaneously hypertensive rat (SHR). In the present study, we aimed to analyze the underlying mechanisms through which such defects are introduced into the D1A receptor protein of SHR.The oxidative state of SHR proximal tubules was analyzed by measuring lipid peroxidation. D1A receptor/G-protein coupling was measured following the induction of oxidative stress in normotensive Wistar–Kyoto (WKY) rats.For the first time, an increased state of oxidative stress was demonstrated in SHR proximal tubules compared with those of normotensive controls, WKY and Sprague–Dawley rats. Lipid peroxidation levels in SHR were significantly higher by 66 and 79%, relative to WKY or Sprague-Dawley rats, respectively. Hydrogen peroxide treatment of proximal tubules from SHR, WKY and Sprague–Dawley rats induced an additional increase in lipid peroxidation in a dose-dependent manner, although the percentage induction was lower in SHR than in WKY and Sprague–Dawley rats. This induction of lipid peroxidation in WKY rats resulted in a loss of D1A/ G-protein coupling, with no decrease in receptor protein. Treatment of WKY rat proximal tubules with an antioxidant, ascorbic acid, or a reducing agent, dithiothreitol, induced D1A receptor/G-protein coupling.These data indicate that D1A receptor/ G-protein coupling is modulated by changes in redox states. Therefore, the D1A receptor/G-protein coupling in SHR may have been damaged by reactive oxygen species released as a result of the elevated oxidative stress seen in the proximal tubules.