Abstract-Eight Na-repleted volunteers underwent 3 separate 90-minute infusions of either N G -nitro-L-arginine methyl ester (L-NAME) 3.0 mg ⅐ kg Ϫ1 ⅐ min Ϫ1 or endothelin-A receptor (ET-A) blocker BQ-123 (BQ) 0.125 nmol ⅐ kg Ϫ1 ⅐ min Ϫ1or both. Mean arterial pressure (MAP), glomerular filtration rate (GFR), renal blood flow (RBF), renal vascular resistances (RVR), and sodium excretion rate (UNaV) were measured at baseline (b) and from 0 to 45 minutes (period 1) and 45 to 90 minutes (period 2) of infusion. BQ alone had no effect. GFR declined by 4.9% (PϽ0.001 versus b) in period 1, to 9.9% (PϽ0.001) in period 2 with L-NAME, and by 3.3% (PϽ0.01) to 6.6% (PϽ0.001) with L-NAME plus BQ (PϭNS between L-NAME and L-NAME plus BQ). UNaV fell equally with L-NAME or L-NAME plus BQ. MAP rose significantly in period 2 with L-NAME (6.9%; PϽ0.001) but not with coinfused BQ (2.1%; PϭNA versus b, Pϭ0.005 versus L-NAME alone). RBF declined by 12.2% (PϽ0.001) to 18.3% (PϽ0.001) with L-NAME and by 4.6% (PϽ0.005) to 8.2% (PϽ0.001) with L-NAME plus BQ. These changes were smaller with L-NAME plus BQ (PϽ0.05 in period 1 and PϽ0.02 in period 2). Blunted changes were also seen for RVR (PϽ0.005 in period 1 and PϽ0.001 in period 2 between L-NAME alone and L-NAME plus BQ). These findings show that systemic and renal vasoconstriction due to L-NAME are attenuated by BQ, which suggests that an interaction between endogenous nitric oxide production and ET-A activity participates in the maintenance of baseline systemic and renal vascular tone in humans.

In seven healthy, young subjects on a 240 mmol sodium diet, mean arterial pressure (MAP), renal hemodynamics, and renal handling of Na and exogenous Li were measured at baseline and during short-term nitric oxide (NO) blockade with a 90-minute infusion of 3.0 microg x kg(-1) x min(-1) of N(G)-L-arginine methyl ester (L-NAME). The infusion was performed twice: after a 3-day pretreatment with either placebo or 50 mg losartan to block Ang II receptors. With placebo, L-NAME produced no change in MAP from 0 to 45 minutes (period 1) and only a 5% increase at 45 to 90 minutes (period 2) of infusion. Effective renal plasma flow (ERPF, PAH clearance) and glomerular filtration rate (GFR, inulin clearance) declined by 11.7% and 8.0%, respectively in period 1 and by 14.6% and 11.6%, respectively, in period 2. Calculated renal vascular resistance (RVR) increased by 13.0% to 20.6%. Fractional excretion of Na (FE(Na)) and Li (FE(Li)) fell by 30.0% and 21.0%, respectively, in period 1 and by 44.2% and 31.1% in period 2. All these variations were significant versus baseline. With losartan, the rise in MAP at 45 to 90 minutes was completely abolished, whereas all changes in ERPF, GFR, RVR, FE(Na), and FE(Li) in response to L-NAME were the same as those observed with placebo. The present data show that NO blockade with low-dose systemic infusion of L-NAME produces renal vasoconstriction, reduced GFR, and increased tubular Na reabsorption independent of changes in MAP. Reduced FE(Li) indicates an effect of NO on the proximal tubule. Since these changes are not prevented by losartan, we conclude that in Na-repleted humans, renal vasoconstriction and Na-retaining effects of inhibition of basal NO production are not due to the unopposed action of endogenous Ang II.

Abstract-To investigate whether endothelin-A receptors and nitric oxide modulate renal hemodynamics in man under angiotensin II receptor-1 blockade, 6 healthy volunteers, on a 240 mmol Na diet, underwent 4 separate renal hemodynamic measurements, in 3 of which endothelin-A blocker BQ-123 0.2 nmol ⅐ kg ⅐ min Ϫ1 was infused for 90 minutes after pretreatment with either placebo, telmisartan 1 mg ⅐ kg ⅐ day Ϫ1 for 3 days, or telmisartan as well, but with co-infusion of both BQ-123 and N G -nitro-L-arginine methylester 0.5 g ⅐ kg ⅐ min Ϫ1 . A fourth infusion was made with N G -nitro-L-arginine methylester alone. No change followed infusion of either N G -nitro-L-arginine methylester alone or BQ-123 alone. With BQ-123 after telmisartan, renal blood flow rose from 916Ϯ56 mL ⅐ min Ϫ1 ⅐ 1.73 m 2 to 1047Ϯ51.2 (PϽ0.001), and renal vascular resistances fell from 89Ϯ7 mm Hg ⅐ min ⅐ L Ϫ1 to 74Ϯ4 (PϽ0.001). These changes were fully abolished by the co-infused N G -nitro-L-arginine methylester. Infusion of BQ-123, devoid of renal hemodynamic effects at baseline, produces significant renal vasodilation when angiotensin II receptors are blocked, indicating an increasing renal hemodynamic role of endothelin-A-receptor activity. Because such a vasodilation is prevented by nonvasoconstricting microdoses of N G -nitro-L-arginine methylester, nitric oxide-endothelin balance controls substantially renal hemodynamics under angiotensin II blockade. These findings are consistent with a rationale of the association of endothelin-A blockers with angiotensin II blockers or angiotensin-converting enzyme inhibitors in treating nitric oxide-deficient conditions such as arterial hypertension, heart failure, and chronic renal diseases. Key Words: angiotensin II Ⅲ nitric oxide Ⅲ endothelin Ⅲ kidney Ⅲ hemodynamics Ⅲ L-NAME Ⅲ receptors, endothelin H emodynamic control in both systemic circulation and kidney results physiologically from a balance of opposing vasodilator systems such as nitric oxide (NO) and prostaglandins, and vasoconstrictor systems. 1 These latter include, besides sympathetic nervous system, the 2 potent peptide vasoconstrictors angiotensin II (Ang II) and endothelin-1 (ET-1), 1 this latter being the predominant isoform of endothelin family expressed in human vasculature. 2 Vasoactive properties of ET-1 are mediated by 2 receptor subtypes, ET A and ET B , both leading to vasoconstriction in vascular smooth muscle cells, whereas activation of ET B in endothelial cells may cause vasodilation through the release of prostacyclin and NO. 2,3 At the kidney level, however, studies in both dogs 4,5 and humans 6,7,8 have indicated the ET A receptor as the main mediator of the vasoconstrictor effect of ET-1.A considerable body of evidence has shown that ET-1, although it is the most potent endogenous vasoconstrictor, assumes a major hemodynamic role and contributes to the end-organ damage, mainly under experimental and clinical pathophysiological conditions. 2,3 Furthermore, a number of interactions have been recognized between Ang II and ET...

Abstract-To investigate whether endothelin-A receptors mediate hemodynamic changes caused by exogenous Angiotensin II in humans, 7 healthy volunteers on a 250-mmol sodium diet underwent 3 separate p-aminohippurate and inulin-based renal hemodynamic studies. In 2 studies, Angiotensin II (increasing rates of 0.625, 1.25, and 2.5 ng/kg per minute, each for 30 minutes) was infused either alone or combined with endothelin-A blocker, BQ123, 0.4 nmol/kg per minute. A third infusion of BQ123 alone was not followed by any change. Key Words: receptors, endothelin Ⅲ angiotensin II Ⅲ kidney Ⅲ hemodynamics Ⅲ human A ngiotensin II (Ang II), a potent endogenous vasoconstricting and sodium-retaining peptide, plays a key role in the regulation of renal function and arterial pressure, 1,2 mostly by activating Ang II-type 1 (AT1) receptors, which leads to elevation in blood pressure, renal vasoconstriction, and sodium retention. Several of such actions are similar to those of endothelin-1 (ET-1), which is the predominant isoform of the endothelin family in human vasculature. 3,4 Vasoactive properties of ET-1 are mediated by two receptor subtypes, ET A and ET B , both leading to vasoconstriction in vascular smooth cells, whereas activation of ET B in endothelial cells causes vasodilation as the result of release of prostacyclin and nitric oxide (NO). 3,4 In humans, however, the ET A receptor is the main mediator of ET-1 renal vasoconstriction. 5-8 ET-1, although it is the most potent endogenous vasoconstrictor, assumes a major hemodynamic role and contributes to the end-organ damage, mainly under experimental pathophysiological conditions. 3,4,9 -11 In most of these, interactions between Ang II and ET-1 may contribute largely to the observed changes. For instance, salt-sensitive hypertension, renal vasoconstriction, and cardiovascular and renal fibrotic damage, produced by chronic administration of exogenous Ang II, can be prevented by inhibition of endogenous ET-1, indicating that ET-1 mediates much of the vasoconstriction caused by chronic Ang II. 9 -11 Furthermore, ET-1 participates in the acute pressor effects of exogenous Ang II 12,13 and partly mediates the vasoconstriction from exogenous Ang II in different vascular beds, including kidney. 14,15 Interestingly, studies in rats have shown that such Ang II-ET-1 interaction may be sodium-dependent, because under elevated sodium intake, ET A blockade inhibited Ang II hypertension much more than under sodium restriction. 16 Ang II also stimulates both ET-1 synthesis and release, 3,4,17 whereas ET-1 enhances the pressor action of Ang II. 18 Finally, ET-1 and Ang II share the same intracellular signaling pathways. 3,17 Thus, ET-1 is generally considered as a powerful mediator of Ang II-dependent vasoconstriction and organ damage under experimental conditions. Conversely, little is known on the role of ET-1 and of its potential interactions with Ang II on systemic and renal hemodynamics in humans. In normal humans, systemic ET A blockade markedly blunts systemic and renal vasoconstr...

Abstract-In eight young healthy subjects on a 240 mM Na diet mean arterial pressure (MAP), renal hemodynamlcs and renal handling of Na and exogenous Ll were measured at baseline and durmg acute nitric oxide (NO) mhlbltlon with 90-minute mfuslon of 3 Opg/kg mm-' of NC-L-argmme methyl ester (L-NAME) The same experiment was repeated with mfuslon of 50pg/kg mm-' of DA, receptor blocker L-Sulpmde (L-SULP) alone and, finally, with simultaneous mfuslon of both L-NAME and L-SULP L-SULP alone did not elicit any effect L-NAME alone produced no changes m MAP from 0 to 45 minutes (PJ and a 6 6% increase at 45 to 90 minutes (P2) of mfuslon Effective renal plasma flow (ERPF, PAH clearance) and glomerular filtration rate (GFR, muhn clearance) declined by 10 2% and 7 6%, respectively, m P, and by 15 3% and 11 5% m P, Flltratlon Fraction (FF) rose by 4 2% m Pz Calculated renal vascular resistance (RVR) increased by 13 0% to 25.6% Fractional excretion of Na (FENa) and L1 (FEL1) fell by 20 0% and by 16.0%, respectively, m P, and by 40 0% and 25 1% m Pz All these vanatlons, except for MAP and GFR, were slgmficantly greater during comfuslon of L-NAME and L-SULP ERPF declined by 17 8% to 33 7%, FENa by 26 7% to 53 3%, FELl by 13 8% to 34 8%, while RVR rose by 22 5% to 59 1% and FF by 10 1% to 29 3% The present data confirm that NO blockade with low-dose systemic mfuslon of L-NAME produces renal vasoconstnctlon, reduced GFR with slight increase m FF, and enhanced tubular Ll, and Na reabsorption Since increase m RVR and FF and decrease m FENa and FELl are markedly potentlated by the simultaneous mfuslon of DA2 blocker L-SULP, which exerts no effects by Itself, we suggest that DA mteractlons between DA system at the level of DA2 receptors and basal NO production play a physlologlcal role m the regulation of renal function m humans (Hypertension, 1998;31[part2]:277-282.)Key Words: DA2 receptor n L-SULP n L-NAME n human n kidney n mtnc oxide n hemodynamlcs T he endogenous cathecolamme dopamme (DA) 1s involved m a wide variety of physlologlcal processes and contributes to modulation of many functions including behavior, movement, nerve conduction, hormone synthesis and release, blood pressure and renal hemodynamlcs, and sodium handling Outside of the central nervous system, DA receptors have been divided on the basis of their locahsatlon into two maJor groups, the presynaptlc (DA,) and postsynaptlc (DA,) subtypes 1~23 Wlthm the kidney, DA, receptors have been localized postsynaptlcally m blood vessels, proximal convoluted tubule, and collectmg duct 133 Increase m ademlcyclase actlvlty, renal vasodllatlon and natnurens, mhlbltable by DA, antagorusts, are known to follow DA, receptor stlmulatlon by infusion of DA or specific DA, agomstlc drugs 1~ DA, receptors have been identified presynaptlcally on sympathetic nerve termmals m the adventltla of the renal vasculature I,* 7 Due to their preJunctlona1 locahsatlon, DA2 receptor actlvatlon 1s thought to mhlblt at that level the NE release thus modulatmg RSNA ',*s3 The physlologcal role of presyn...