Myogenic Responses of Mouse Isolated Perfused Renal Afferent Arterioles: Effect of Salt Intake and Reduced Renal Mass

Abstract

Renal autoregulation is mediated by myogenic vasoconstriction and tubuloglomerular feedback. Since defects may contribute to renal barotrauma in salt‐sensitive hypertension and chronic kidney disease, we tested the hypothesis that the myogenic response is diminished by dietary salt or the reduced renal mass (RRM). Afferent arterioles (Af) were dissected from 1 2/3 nephrectomized RRM mice and sham‐operated controls and perfused during step changes in pressure from 0 to 140 mmHg. The active wall tension (AWT) was the differences with physiologic perfusate, compared to zero calcium + EGTA. The MAP of conscious mice by telemetry (85 ± 4 mmHg) was unaffected by salt intake or RRM. Af developed a linear increase in AWT above a perfusion pressure of 60 ± 6 mmHg without plateau. The slope of AWT vs perfusion pressure defined the myogenic response. This response was similar in mice fed normal or high salt for 3 months (3.5±0.3 vs 3.9 ± 0.5 dynes μcm−1/mmHg, p>0.05). It was unaffected after 3 days or 3 weeks of RRM but was reduced by 28±3% and 60±7% (p<0.05) in the normal and high salt RRM groups at 3 months (2.5 ± 0.3 and 1.6 ± 0.3 dynes·cm−1/mmHg). We conclude that the mouse renal Af develops a linear increase in myogenic tone above ambient perfusion pressure that could safeguard against renal barotrauma. The normal myogenic response is not dependent on salt intake, but is impaired substantially in RRM, especially during high salt intake.