Nebivolol induced vasodilation of renal afferent arterioles involves 1 β 3 adrenergic receptor and nitric oxide synthase activation

: Nebivolol is a β 1 adrenergic blocker that also elicits renal vasodilation and increases GFR. However, its direct actions on the renal microvasculature and vasodilator mechanism have 28 not been established. We used the in vitro blood-perfused juxtamedullary nephron technique to 29 determine the vasodilator effects of nebivolol and to test the hypothesis that nebivolol induces 30 vasodilation of renal afferent arterioles via an NOS/NO/sGC/cGMP pathway and the afferent 31 arteriolar vasodilation effect may be mediated through the release of NO by activation of NOS 32 via a β 3 adrenoceptor dependent mechanism. Juxtamedullary nephrons were superfused with 33 nebivolol either alone or combined with the sGC inhibitor, ODQ or the NOS inhibitor, L-NNA 34 or β blockers: metoprolol ( β 1), butoxamine ( β 2), SR59230A ( β 3). Nebivolol (100µmol/L) 35 markedly increased afferent & efferent arteriolar diameters by 18.9±3.0% & 15.8±1.8%. 36 Pretreatment with L-NNA (1000µmol/L) or ODQ (10µmol/L) decreased afferent vasodilator 37 diameters and prevented the vasodilator effects of nebivolol (2.0±0.2%, 2.4±0.6%). Metoprolol 38 did not elicit significant changes in afferent vasodilator diameters and did not prevent the effects 39 of nebivolol to vasodilate afferent arterioles. However, treatment with SR59230A, but not 40 butoxamine, markedly attenuated the vasodilation responses to nebivolol. Using a monoclonal antibody to β 3 receptors revealed predominant immunostaining on vascular & glomerular endothelial cells. These data indicate that nebivolol vasodilates both afferent and efferent 43 arterioles and that the afferent vasodilator effect is via a mechanism that is independent of β 1 44 receptors but is predominantly mediated via a NOS-NO-sGC-cGMP dependent mechanisms 45 initiated by activation of endothelial β 3 receptors. its vasodilating properties. the effects of nebivolol on afferent and efferent arteriolar vascular tone have not been established. The present study was performed to determine the magnitude of the juxtamedullary afferent and efferent arteriolar responses to nebivolol and the roles of nitric oxide synthase and soluble guanylate cyclase in mediating nebivolol-induced vasodilatory responses in afferent arterioles. The detailed studies were focused on afferent arterioles as the model system to evaluate the hypothesis that nebivolol induces vasodilation of renal afferent arterioles of juxtamedullary nephron via an NOS/NO/sGC/cGMP pathway. We also tested the hypothesis that the afferent arteriolar vasodilation effect may be mediated through the release of NO by activation of NOS via a β 3 adrenoceptor dependent mechanism. While β 3 -adrenoreceptor mRNA has been shown in and and the the localization of β 3 -adrenoreceptors in the renal microvasculature. Accordingly, immunohistochemical studies were performed to localize β 3 adrenoceptors in kidney. determine the dose response relationships for Afferent arteriolar inside diameters sequential superfusate experiments determine the effects of nitric oxide synthase inhibition by L-NNA on the nebivolol afferent arterioles. Afferent arteriolar inside diameters were sequential of the superfusate solutions: nebivolol at 1, 10 and dose response experiments). L-NNA followed by nebivolol was repeated at 1, 10 and A third series of experiments was performed to determine the effects of soluble guanylate cyclase inhibition by ODQ on the nebivolol mediated vasodilation of afferent arterioles. Afferent arteriolar inside diameters were measured during sequential exposure of the kidney to the following superfusate solutions: A) control vehicle; 10µmol/L ODQ; B) control ODQ followed nebivolol at 1, 10 and A fourth series of experiments was performed to determine the direct effects of different β 1 adrenergic receptor blocker and also to test vasodilatory effect of nebivolol suggesting a minor possible role mediated by β 2 -adrenoceptors. In contrast, nebivolol induced afferent arteriolar vasodilation was markedly attenuated after blocking β 3 - adrenoceptors with SR 59230A indicating an agonist effect of nebivolol on endothelial beta3- adrenergic receptors, thus suggesting that the vasodilator effect of nebivolol is mediated through the release of NO via a β 3 adrenoceptor–dependent mechanism. These results are supported further by our current immunohistochemical data revealing the presence of β 3-adrenoceptors on endothelial cells of renal arterioles and glomerular capillaries suggesting their functional role to activate β 3 -adrenoceptors and NOS, and elicit renal vasodilation. These findings fit well with functional studies in coronary arteries and other tissues showing that the vasodilator effects of nebivolol is mediated via activation of endothelial beta3-adrenergic receptors (7, 8, 20, 27, 43, 33) and molecular studies showing that β 3 - adrenoceptors are expressed in the kidney (31, 50), the endothelial cells of aorta (3) and human coronary resistance arteries (8). These results have important implications for the pathways involved in adrenergic modulation of eNOS pathways in the vascular wall These findings provide mechanistic insights suggesting that β 3 -adrenergic receptors may respond to excessive renal sympathetic nerve activation by providing a counteracting renal protective influence to prevent excessive renal vasoconstriction during states of elevated sympathetic The effects of nebivolol to vasodilate renal afferent and efferent arterioles is of potential clinical relevance for conditions related to treatment of hypertension and associated cardiovascular disorders where there is evidence of renal vasoconstriction. The renal microvasculature plays a crucial role in the control of blood pressure. NO-mediated renal vasodilation is impaired in hypertension and diabetes due to decrease NO bioavailability, NOS activity and NO-cGMP signaling. The present study provides direct data demonstrating that nebivolol elicits vasodilation of the renal microvasculature and suggests that the major pathway is via β 3 -adrenergic receptor 403 and NOS activation. Nebivolol induced renal vasodilation could be of benefit in the treatment of hypertension and associated cardiovascular disorders associated with hypertension and endothelial dysfunction.