Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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Increased peripheral resistance may be associated with essential hypertension. We have shown that myogenic (pressure-induced) constriction was enhanced in arterioles from hypertensive compared to normotensive animals. Therefore, our objective was to determine if this enhanced myogenic constriction was endothelium dependent. We utilized isolated, cannulated, arterioles (80 to 110 microns) from the rat cremaster muscle of Spontaneously Hypertensive (SH) and Normotensive (WKY) rats. Diameter was measured in response to step changes in intraluminal pressure with and without an intact endothelium. Intrinsic tone developed (approx. 74% of passive). A comparison of the pressure-diameter relationships of both SH and WKY demonstrated that the myogenic response from 50 to 150 cmH2O was endothelium-independent. However, endothelium denudation abolished tone at pressures greater than 170 cmH2O. In other experiments, the SH endothelium-dependent arteriolar constriction remained intact after inhibiting the formation of prostaglandins with diclofenac (10-5M; 30 minutes). In contrast, treatment with the endothelin-A (ET-A) receptor antagonist, BQ-123 (10-7M; 30 minutes), abolished the high pressure tone without altering endothelium-independent responses. These data suggest that the endothelium of larger microvessels responds to high pressure by releasing the vasoconstrictor endothelin; perhaps to protect smaller vessels (those with little or no smooth muscle) from damaging pressure while themselves adding to peripheral resistance.

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Presentation Number SAfalcone0356
Keywords: endothelin, endothelium, arteriole, skeletal muscle, hypertension