In uncomplicated essential hypertension, renal blood flow, glomerular filtration rate, and glomerular capillary pressure are within the normal range despite elevated renal perfusion pressure, suggesting abnormally high resistance of the preglomerular vessels. Among various preglomerular vascular segments, the afferent arteriole (Af-Art) is thought to be the site responsible for most resistance. However, little is known about the vascular reactivity of the Af-Art or its alteration in hypertension. In this study, we tested the hypothesis that pressureinduced constriction is exaggerated in Af-Arts from spontaneously hypertensive rats (SHRs). Single Af-Arts were microdissected from kidneys of SHRs and normotensive control Wistar-Kyoto (WKY) rats and were microperfused in vitro. When pressure in the Af-Art was increased stepwise from 20 to 80 mm Hg, luminal diameter increased similarly in both WKY and SHR Af-Arts (from 10.0±0.8 to 18.6±1.3 fim and from 10.1±1.2 to 16.9±1.5 μm, respectively). However, when pressure was further increased to 140 mm Hg, the diameter remained unchanged in WKY Af-Arts (19.2±1.9 μm), whereas it decreased significantly to 11.1±0.9 μn in those from SHRs. We conclude that pressure-induced constriction is exaggerated in SHR Af-Arts, which may contribute to the development and maintenance of hypertension.
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