Endothelin (ET) receptor blockade delays the progression of diabetic nephropathy; however, the mechanism of this protection is unknown. Therefore, the aim of this study was to test the hypothesis that ET A receptor blockade attenuates superoxide production and inflammation in the kidney of diabetic rats. Diabetes was induced by streptozotocin (diabetic rats with partial insulin replacement to maintain modest hyperglycemia [HG]), and sham rats received vehicle treatments. Some rats also received the ET A antagonist ABT-627 (sham؉ABT and HG؉ABT; 5 mg/kg per d; n ‫؍‬ 8 to 10/group). During the 10-wk study, urinary microalbumin was increased in HG rats, and this effect was prevented by ET A receptor blockade. Indices of oxidative stress, urinary excretion of thiobarbituric acid reactive substances, 8-hydroxy-2-deoxyguanosine, and H 2 O 2 and plasma thiobarbituric acid reactive substances were significantly greater in HG rats than in sham rats. These effects were not prevented by ABT-627. In addition, renal cortical expression of 8-hydroxy-2-deoxyguanosine and NADPH oxidase subunits was not different between HG and HG؉ABT rats. ET A receptor blockade attenuated increases in macrophage infiltration and urinary excretion of TGF-␤ and prostaglandin E 2 metabolites in HG rats. Although ABT-627 did not alleviate oxidative stress in HG rats, inflammation and production of inflammatory mediators were reduced in association with prevention of microalbuminuria. These observations indicate that ET A receptor activation mediates renal inflammation and TGF-␤ production in diabetes and are consistent with the postulate that ET A blockade slows progression of diabetic nephropathy via an anti-inflammatory mechanism.

Abstract-The mechanotransduction mechanism underlying the myogenic response is poorly understood, but evidence implicates participation of epithelial sodium channel (ENaC)-like proteins. Therefore, the role of ENaC on the afferent arteriolar myogenic response was investigated in vitro using the blood-perfused juxtamedullary nephron technique. Key Words: myogenic response Ⅲ epithelial sodium channel Ⅲ amiloride Ⅲ benzamil Ⅲ juxtamedullary nephrons Ⅲ autoregulatory response R enal autoregulatory behavior maintains a relatively constant renal blood flow despite changes in renal arterial pressure, a vital renal function for preventing hypertensioninduced renal injury. [1][2][3] In kidneys, autoregulation is accomplished through the combined influences of the myogenic and tubuloglomerular feedback (TGF) mechanisms. 4 The TGF response is a process by which the macula densa senses changes in distal tubule NaCl delivery and, in turn, modulates release of paracrine signals that alter afferent arteriolar tone. 5 The myogenic response is an intrinsic property of preglomerular arteries and afferent arterioles. Myogenic responses are characterized by vasoconstriction after an increase in transmural pressure or vasorelaxation after a decrease in transmural pressure. 6 The myogenic response is inherent to vascular smooth muscle and independent of endothelium. 7 Myogenic behavior is also observed in vascular elements of many other organs such as coronary, cerebral, and mesenteric arteries and cremaster arterioles and reflects an important mechanism for establishing ambient vascular tone and maintaining a relatively constant regional blood flow and capillary hydrostatic pressure. [7][8][9] The cellular mechanisms by which an increase in arterial pressure triggers the myogenic response have been investigated intensively. It is well established that increasing local transmural pressure leads to membrane depolarization of vascular smooth muscle cells, activation of voltage-gated L-type calcium channels, and vasoconstriction. 10 -13 However, the mechanisms by which the mechanical stimuli lead to activation of myogenic signaling cascades remain poorly understood.Currently several hypotheses have been proposed for linking mechanical stimuli to the cellular events producing a myogenic response. These include involvement of stretchactivated cation channels, perturbation of the actin cytoskeleton, specialized membrane domains, or extracellular matrix proteins such as integrins. 8,9,14 -16 The role of stretch-activated cation channels in the myogenic response was indirectly demonstrated in isolated perfused hydronephrotic rat kidneys lacking TGF responses. 17 In this model, pressure-mediated

Sphingosine-1-phosphate (S1P), a bioactive sphingolipid metabolite, has been implicated in regulating vascular tone and participating in chronic and acute kidney injury. However, little is known about the role of S1P in the renal microcirculation. Here, we directly assessed the vasoresponsiveness of preglomerular and postglomerular microvascular segments to exogenous S1P using the in vitro blood-perfused juxtamedullary nephron preparation. Superfusion of S1P (0.001-10 mM) evoked concentration-dependent vasoconstriction in preglomerular microvessels, predominantly afferent arterioles. After administration of 10 mM S1P, the diameter of afferent arterioles decreased to 35%65% of the control diameter, whereas the diameters of interlobular and arcuate arteries declined to 50%612% and 68%66% of the control diameter, respectively. Notably, efferent arterioles did not respond to S1P. The S1P receptor agonists FTY720 and FTY720-phosphate and the specific S1P1 receptor agonist SEW2871 each evoked modest afferent arteriolar vasoconstriction. Conversely, S1P2 receptor inhibition with JTE-013 significantly attenuated S1P-mediated afferent arteriolar vasoconstriction. Moreover, blockade of L-type voltage-dependent calcium channels with diltiazem or nifedipine attenuated S1P-mediated vasoconstriction. Intravenous injection of S1P in anesthetized rats reduced renal blood flow dose dependently. Western blotting and immunofluorescence revealed S1P1 and S1P2 receptor expression in isolated preglomerular microvessels and microvascular smooth muscle cells. These data demonstrate that S1P evokes segmentally distinct preglomerular vasoconstriction via activation of S1P1 and/or S1P2 receptors, partially via L-type voltagedependent calcium channels. Accordingly, S1P may have a novel function in regulating afferent arteriolar resistance under physiologic conditions. 25: 177425: -178525: , 201425: . doi: 10.1681 Sphingosine 1-phosphate (S1P) is recognized as an important signaling molecule in diverse biologic processes. 1,2 Growing evidence indicates that S1P plays an important role in regulating vascular reactivity. 3-5 S1P is a bioactive sphingolipid metabolite and is released from erythrocytes, platelets, and endothelial cells. 6,7 The majority of S1P effects are mediated via five distinct receptors (S1P1-S1P5 receptors), which represent a family of small G proteincoupled receptors (GPCRs) 5 ; however, S1P can also exist in the cytoplasm as a second messenger involved in Ca 2+ mobilization or cell survival and proliferation. 8,9 S1P1-S1P3 receptors are expressed by a wide variety of tissues, whereas S1P4 and S1P5 receptors are mainly expressed in cells of the immune and nervous systems. 4,10 In the vasculature, endothelial cells mainly express S1P1 and S1P3 with variable expression of S1P2, whereas vascular smooth muscle cells express S1P2 and S1P3 with variable expression of S1P1. [3][4][5] Studies in animals show that application of exogenous S1P J Am Soc Nephrol

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