title: Role of oxidative stress in defective renal dopamine D1 receptor-G protein coupling and function in old Fischer 344 rats.
abstract: Aging is associated with an increase in oxidative stress. Previously, we have reported that dopamine failed to inhibit proximal tubular Na-K-ATPase and to promote sodium excretion in old rats (Beheray S, Kansra V, Hussain T, and Lokhandwala MF. Kidney Int 58: 712-720, 2000). This was due to uncoupling of dopamine D1 receptors from G proteins resulting from hyperphosphorylation of D1 receptors. The present study was designed to test the role of oxidative stress in the age-related decline in renal dopamine D1 receptor function. We observed that old animals had increased malondialdehyde (MDA) levels, a biomarker of oxidative stress, and decreased D1 receptor number and protein in the proximal tubules (PT) compared with adult rats. In old rats, there was increased G protein-coupled receptor kinase-2 (GRK-2) abundance, increased basal serine phosphorylation of D1 receptors, and defective D1 receptor-G protein coupling in PT membranes. Interestingly, supplementation with an antioxidant, tempol (1 mmol/l in drinking water for 15 days), lowered MDA levels and normalized D1 receptor number and protein in old rats to the level seen in adult rats. Furthermore, tempol decreased GRK-2 abundance and D1 receptor serine phosphorylation and restored D1 receptor-G protein coupling in PT of old rats. The functional consequence of these changes was the restoration of the natriuretic response to D1 receptor activation in tempol-supplemented old rats. Therefore, in old rats, tempol reduces oxidative stress and prevents GRK-2 membranous abundance and hyperphosphorylation of D1 receptors, resulting in restoration of D1 receptor-G protein coupling and the natriuretic response to SKF-38393. Thus tempol, by lowering oxidative stress, normalizes the age-related decline in dopamine receptor function.
authors.affiliation: Heart and Kidney Institute, College of Pharmacy, Univ. of Houston, Houston, TX 77204-5041, USA.
authors.forename: Riham Zein
authors.initials: RZ
authors.lastname: Fardoun
authors.forename: Mohammad
authors.initials: M
authors.lastname: Asghar
authors.forename: Mustafa
authors.initials: M
authors.lastname: Lokhandwala
mesh_terms: D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000494:pharmacology; D000375:Aging / Q000378:metabolism*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D003497:Cyclic N-Oxides / Q000494:pharmacology; D018491:Dopamine Agonists / Q000494:pharmacology; D054769:G-Protein-Coupled Receptor Kinase 2; D007275:Injections, Intravenous; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism; D009318:Natriuresis / Q000187:drug effects / Q000502:physiology; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D011916:Rats, Inbred F344; D017447:Receptors, Dopamine D1 / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D012964:Sodium / Q000652:urine; D013113:Spin Labels; D014867:Water / Q000378:metabolism; D051552:beta-Adrenergic Receptor Kinases / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D003497:Cyclic N-Oxides; D018491:Dopamine Agonists; D017447:Receptors, Dopamine D1; D013113:Spin Labels; D014867:Water; D012694:Serine; D008315:Malondialdehyde; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D012964:Sodium; C496569:Grk2 protein, rat; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; C001803:tempol