Effect of angiotensin II and norepinephrine on isolated rat afferent and efferent arterioles.

Differential sensitivity of the pre- and postglomerular arterial vessels to vasoconstrictor activity of angiotensin II (ANG II) and norepinephrine (NE) is controversial. To avoid the complex extravascular neurohumoral variables that may have accounted for different results in the intact rat kidney, an isolated arteriole technique was used to examine the dose responses of ANG II and NE on afferent (AA) and efferent arterioles (EA) from Sprague-Dawley rats. EA were more sensitive than AA to ANG II (EC50 = 3.2 +/- 1.8 x 10(-11) and 1.0 +/- 1.6 x 10(-9) M, respectively, P less than 0.001), whereas EC50 of both AA and EA to NE were similar (3.4 +/- 2.3 x 10(-8) and 1.4 +/- 2.6 x 10(-8) M, respectively). The dose-response curves of AA to ANG II were not different when perfused at different luminal pressures (90 and 30 mmHg). In contrast, EA were more sensitive to ANG II at 30 than at 90 mmHg (3.0 +/- 1.2 x 10(-11) and 5.0 +/- 1.8 x 10(-10) M, respectively, P less than 0.005). The EC50 of EA to NE was unaffected by similar changes in luminal pressures. The mean dose-response curves of AA to ANG II were the same with and without the addition of 10(-5) M indomethacin; however, in arterioles displaying a focal constriction pattern to ANG II the response became uniform. It is concluded that, in the isolated rat glomerular arterioles, EA are more sensitive to ANG II than AA, but both vessels respond similarly to NE. The decreased ANG II sensitivity in AA is not related to the higher in vivo pressure, and the attenuated response in AA does not appear to be mediated primarily through ANG II-stimulated vasodilator prostanoid activity. EA sensitivity to ANG II appears to be inversely related to lumen pressure.