Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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The aims of this study were to determine if hypertension and/or high salt intake can alter the myogenic behavior of proximal arterioles in striated muscle, and to assess the modulation of this behavior by endogenous nitric oxide (NO). Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) fed low-salt (0.45%, LS) or high-salt (7%, HS) diets were enclosed in a ventilated airtight box with the spinotrapezius muscle exteriorized for intravital microscopy. Mean arterial pressure was resistant to dietary salt in WKY (LS: 96±6 mm Hg, HS: 98±11 mm Hg), whereas it was significantly higher and augmented by dietary salt in SHR (LS: 163±4 mm Hg, HS: 205±3 mm Hg). Resting arteriolar diameters (D, 40±3 to 47±4 mm), wall shear rates (WSR, 579±44 to 728±132 s-1) and volume flows (Q, 4±1 to 7±1 nl/s) were not different among groups. In all groups, box pressurization to 30 mm Hg caused the same increase in arteriolar transmural pressures (servo-null method), resulting in immediate arteriolar constriction. These myogenic responses were similar in WKY and SHR (constrictions of 19±2% in WKY-LS vs 17±5% in SHR-LS). High salt intake reduced myogenic responses in WKY (7±5% constriction) but not in SHR (27±5% constriction). Constriction magnitude did not correlate with resting WSR or Q in any group, and constriction was sustained despite secondary increases in WSR and decreases in Q. Inhibition of NO synthesis (NG-monomethyl-L-arginine) augmented myogenic responses to a similar extent in WKY-LS (36±3%) and SHR-LS (35±6%.), but had no effect in WKY-HS or SHR-HS. Therefore, high dietary salt may alter local blood flow control by suppressing (1) the myogenic activity of proximal arterioles in normotensive rats, and (2) the influence of NO on this activity in normotensive and hypertensive rats. (Supported by NIH HL-44012 and HL-52019

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Presentation Number SAnurkiewicz0617
Keywords: myogenic response, microcirculation, nitric oxide, dietary salt, hypertension