Renal dopaminergic defect in C57Bl/6J mice

1 Children's National Medical Center, Center for Molecular Physiology Research, Department of Pediatrics, George Washington School of Medicine and Health Sciences, Washington, DC; and 2 Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas Submitted March 12, 2009 ; accepted in final form August 28, 2009 The C57Bl/6J mouse strain, the genetic background of many transgenic and gene knockout models, is salt sensitive and resistant to renal injury. We tested the hypothesis that renal dopaminergic function is defective in C57Bl/6J mice. On normal NaCl (0.8%, 1 wk) diet, anesthetized and conscious (telemetry) blood pressures were similar in C57Bl/6J and SJL/J mice. High NaCl (6%, 1 wk) increased blood pressure ( 30%) in C57Bl/6J but not in SJL/J mice and urinary dopamine to greater extent in SJL/J than in C57Bl/6J mice. Absolute and fractional sodium excretions were lower in SJL/J than in C57Bl/6J mice. The blood pressure-natriuresis plot was shifted to the right in C57Bl/6J mice. Renal expressions of D 1 -like (D 1 R and D 5 R) and angiotensin II AT 1 receptors were similar on normal salt, but high salt increased D 5 R only in C57Bl/6J. GRK4 expression was lower on normal but higher on high salt in C57Bl/6J than in SJL/J mice. Salt increased the excretion of microalbumin and 8-isoprostane (oxidative stress marker) and the degree of renal injury to a greater extent in SJL/J than in C57Bl/6J mice. A D 1 -like receptor agonist increased sodium excretion whereas a D 1 -like receptor antagonist decreased sodium excretion in SJL/J but not in C57Bl/6J mice. In contrast, parathyroid hormone had a similar natriuretic effect in both strains. These results show that defective D 1 -like receptor function is a major cause of salt sensitivity in C57Bl/6J mice, decreased renal dopamine production might also contribute. The relative resistance to renal injury of C57Bl/6J may be a consequence of decreased production of reactive oxygen species. angiotensin II receptors; dopamine receptors; GRK4; reactive oxygen species Address for reprint requests and other correspondence: I. Armando, 111 Michigan Ave., NW, Washington, DC 20010 (e-mail: iarmando{at}cnmc.org ).