Function of angiotensin II type 2 receptor in the postglomerular efferent arteriole

The balance of vasucular tone between afferent (Af-Art) and efferent arterioles (Ef-Art) is a critical determinant of the glomerular hemodynamics. We recently reported that selective activation of angiotensin II type 2 receptor (AT-2R) causes dilation in the Af-Art. However, the functional role of AT-2R in the Ef-Art has not been defined. In the present study, we microperfused rabbit Ef-Art in vitro, and examined the effect of angiotensin II (Ang II; 10^-11 to 10^-8 M) on the luminal diameter in the presence or absence of an AT-2R antagonist PD123319 (PD; 10^-7 M). Angiotensin II caused dose-dependent constriction in Ef-Arts, with a significant constriction occurring at 10^-11 M; at 10^-10 M the diameter decreased by 28 ± 4% (N = 6). Pretreatment with PD significantly (P < 0.0125) augmented vasoconstrictor action of Ang II; at 10^-10 M the diameter decreased by 44 ± 4% (N = 6). We then examined whether blockade of Ang II type 1 receptor (AT-1R) uncovers vasodilator action of Ang II mediated by AT-2R. Efferent arterioles were preconstricted by about 40% with norepinephrine and AT-1R was blocked with its selective antagonist CV11974 (CV; 10^-8 M). Angiotensin II added to preconstricted and CV-pretreated Ef-Arts caused a dose-dependent dilation; at 10^-8 M diameter increased by 28 ± 3% (N = 5). The dilation was completely abolished by simultaneous pretreatment with PD (N = 4). Our results demonstrate that in the Ef-Art selective activation of AT-2R causes vasodilation, which opposes the vasoconstrictor action of Ang II.