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We investigated the significance of the primary cilia on the macula densa and thick ascending limb (TAL) in regulation of renal hemodynamics, sodium excretion, and blood pressure in this study. A tissue-specific primary cilia knock-out (KO) mouse line was generated by crossing NKCC2-Cre mice with IFT88-Δ/flox mice (NKCC2 CRE ; IFT88Δ /flox ), in which the primary cilia were deleted from the macula densa and TAL. NO generation was measured with a fluorescent dye (4,5-diaminofluorescein diacetate) in isolated perfused juxtaglomerular apparatus. Deletion of the cilia reduced NO production by 56% and 42% in the macula densa and TAL, respectively. NO generation by the macula densa was inhibited by both a nonselective and a selective nitric oxide synthesis inhibitors, whereas TAL-produced NO was inhibited by a nonselective and not by a selective NO synthesis 1 inhibitor. The tubuloglomerular feedback response was enhanced in the KO mice both in vitro measured with isolated perfused juxtaglomerular apparatuses and in vivo measured with micropuncture. In response to an acute volume expansion, the KO mice exhibited limited glomerular filtration rate elevation and impaired sodium excretion compared with the wild-type mice. The mean arterial pressure measured with telemetry was the same for wild-type and KO mice fed a normal salt diet. After a high salt diet, the mean arterial pressure increased by 17.4±1.6 mm Hg in the KO mice. On the basis of these findings, we concluded that the primary cilia on the macula densa and TAL play an essential role in the control of sodium excretion and blood pressure., (© 2017 The Authors.)

We recently showed that α, β, and γ splice variants of neuronal nitric oxide synthase (NOS1) expressed in the macula densa and NOS1β accounts for most of the NO generation. We have also demonstrated that the mice with deletion of NOS1 specifically from the macula densa developed salt-sensitive hypertension. However, the global NOS1 knockout (NOS1KO) strain is neither hypertensive nor salt sensitive. This global NOS1KO strain is actually an NOS1αKO model. Consequently, we hypothesized that inhibition of NOS1β in NOS1αKO mice induces salt-sensitive hypertension. NOS1αKO and C57BL/6 wild-type (WT) mice were implanted with telemetry transmitters and divided into 7-nitroindazole (10 mg/kg/d)-treated and nontreated groups. All of the mice were fed a normal salt (0.4% NaCl) diet for 5 days, followed by a high-salt diet (4% NaCl). NO generation by the macula densa was inhibited by >90% in WT and NOS1αKO mice treated with 7-nitroindazole. Glomerular filtration rate in conscious mice was increased by ≈ 40% after a high-salt diet in both NOS1αKO and WT mice. In response to acute volume expansion, glomerular filtration rate, diuretic and natriuretic response were significantly blunted in the WT and knockout mice treated with 7-nitroindazole. Mean arterial pressure had no significant changes in mice fed a high-salt diet, but increased ≈ 15 mm Hg similarly in NOS1αKO and WT mice treated with 7-nitroindazole. We conclude that NOS1β, but not NOS1α, plays an important role in control of sodium excretion and hemodynamics in response to either an acute or a chronic salt loading., (© 2016 American Heart Association, Inc.)

Morbidity and mortality attributable to hypertension are higher in black essential hypertensive (EH) compared with white EH patients, possibly related to differential effects on vascular injury and repair. Although circulating endothelial progenitor cells (EPCs) preserve endothelial integrity, inflammatory endothelial cells (IECs) detach from sites of injury and represent markers of vascular damage. We hypothesized that blood levels of IECs and inflammatory markers would be higher in black EH compared with white EH patients. Inferior vena cava and renal vein levels of CD34+/KDR+ (EPC) and VAP-1+ (IEC) cells were measured by fluorescence-activated cell sorting in white EH and black EH patients under fixed sodium intake and blockade of the renin-angiotensin system, and compared with systemic levels in normotensive control subjects (n=19 each). Renal vein and inferior vena cava levels of inflammatory cytokines and EPC homing factors were measured by Luminex. Blood pressure, serum creatinine, lipids, and antihypertensive medications did not differ between white and black EH patients, and EPC levels were decreased in both. Circulating IEC levels were elevated in black EH patients, and inversely correlated with EPC levels (R(2)=0.58; P=0.0001). Systemic levels of inflammatory cytokines and EPC homing factors were higher in black EH compared with white EH patients, and correlated directly with IECs. Renal vein inflammatory cytokines, EPCs, and IECs did not differ from their circulating levels. Most IECs expressed endothelial markers, fewer expressed progenitor cell markers, but none showed lymphocyte or phagocytic cell markers. Thus, increased release of cytokines and IECs in black EH patients may impair EPC reparative capacity and aggravate vascular damage, and accelerate hypertension-related complications.

Chronic aldosterone administration increases glomerular filtration rate, whereas inhibition of mineralocorticoid receptors (MRs) markedly attenuates glomerular hyperfiltration and hypertension associated with primary aldosteronism or obesity. However, the mechanisms by which aldosterone alters glomerular filtration rate regulation are poorly understood. In the present study, we hypothesized that aldosterone suppresses tubuloglomerular feedback (TGF) via activation of macula densa MR. First, we observed the expression of MR in macula densa cells isolated by laser capture microdissection and by immunofluorescence in rat kidneys. Second, to investigate the effects of aldosterone on TGF in vitro, we microdissected the juxtaglomerular apparatus from rabbit kidneys and perfused the afferent arteriole and distal tubule simultaneously. Under control conditions, TGF was 2.8±0.2 μm. In the presence of aldosterone (10(-8) mol/L), TGF was reduced by 50%. The effect of aldosterone to attenuate TGF was blocked by the MR antagonist eplerenone (10(-5) mol/L). Third, to investigate the effect of aldosterone on TGF in vivo, we performed micropuncture, and TGF was determined by maximal changes in stop-flow pressure P(sf) when tubular perfusion rate was increased from 0 to 40 nL/min. Aldosterone (10(-7) mol/L) decreased ΔP(sf) from 10.1±1.4 to 7.7±1.2 mm Hg. In the presence of l-NG-monomethyl arginine citrate (10(-3) mol/L), this effect was blocked. We conclude that MRs are expressed in macula densa cells and can be activated by aldosterone, which increases nitric oxide production in the macula densa and blunts the TGF response.

Macula densa cells produce superoxide (O2-) during tubuloglomerular feedback primarily via NAD(P)H oxidase (NOX). The purpose of the present study was to determine NOXs expressed by the macula densa and the role of each one in NaCl-induced O2- production. To identify which isoforms are expressed, we applied single-cell RT-PCR to macula densa cells isolated by laser capture microdissection and to MMDD1 cells (a macula densa-like cell line). The captured cells expressed neuronal NOS (marker of macula densa), NOX2, and NOX4 but not NOX1. Expression of the NOXs and neuronal NOS was essentially identical in the MMDD1 cells. Thus, we used MMDD1 cells to investigate which isoform is responsible for NaCl-induced O2- production. We used small-interfering RNA to knock down NOX2 or NOX4 in MMDD1 cells and measured O2- exposed to low-salt solution (LS; 70 mmol/L of NaCl) or high-salt solution (HS; 140 mmol/L of NaCl). Exposing control cells (scrambled small-interfering RNA) to HS increased O2- concentrations from 0.75+/-0.28 to 1.48+/-0.46 U/min per 10(5) cells in LS and HS, respectively (P<0.001). Inhibiting NOX2 blocked the HS-induced increase in O2- (0.62+/-0.39 versus 0.76+/-0.31 U/min per 10(5) cells in LS and HS groups, respectively). Blocking NOX4 did not affect HS-induced O2- levels. O2- levels in the control cells during LS and HS were 0.80+/-0.30 and 1.56+/-0.49 U/min per 10(5) cells, respectively (P<0.001); whereas O2- levels in NOX4-small-interfering RNA-treated cells during LS and HS were 0.40+/-0.25 and 1.26+/-0.51 U/min per 10(5) cells, respectively (P<0.001). We conclude that, whereas macula densa cells express the NOX2 and NOX4 isoforms, NOX2 is primarily responsible for NaCl-induced O2- generation.

There is substantial evidence suggesting that angiotensin II plays an important role in elevating blood pressure of spontaneously hypertensive rats, despite normal plasma renin activity, and that converting enzyme inhibitors (captopril) can effectively normalize blood pressure in the spontaneously hypertensive rats. One mechanism by which angiotensin II induces hypertension is via oxidative stress and endothelin, as seen in subpressor angiotensin II-induced hypertension. In fact, it has been shown that antioxidants lower mean arterial pressure in spontaneously hypertensive rats. However, the relationship between angiotensin II, oxidative stress, and endothelin in the spontaneously hypertensive rats is still relatively undefined. This study examines the relationship between mean arterial pressure, plasma renin activity, angiotensin II, oxidative stress, and endothelin in spontaneously hypertensive rats compared with normotensive Wistar Kyoto rats, and the effects of captopril on this association. Untreated spontaneously hypertensive rats had increased plasma angiotensin II levels despite normal plasma renin activity, oxidative stress, and endothelin. Captopril treatment in spontaneously hypertensive rats lowered mean arterial pressure, angiotensin II, oxidative stress, and endothelin, and increased plasma renin activity. In contrast, captopril increased plasma renin activity (suggesting effective captopril treatment) but did not significantly alter mean arterial pressure, angiotensin II, oxidative stress, or endothelin of Wistar Kyoto rats. These results suggest that in spontaneously hypertensive rats, angiotensin II is a primary instigator of hypertension, and that captopril selectively lowers angiotensin II, oxidant stress, and endothelin, which in turn may contribute to the blood pressure-lowering efficacy of captopril in spontaneously hypertensive rats.

We examined whether interactions between angiotensin II (Ang II), endothelin (ET), nitric oxide (NO), and prostaglandins (PGs) differentially regulate perfusion to distinct vascular beds. For this, we blocked either angiotensin AT1 or ET receptors or both and then sequentially inhibited NO and PG synthesis in anesthetized dogs. Blocking Ang II or ET had similar effects on systemic hemodynamics: Mean arterial pressure fell slightly without altering cardiac output. Blocking both caused a synergistic fall in mean arterial pressure and increased cardiac output. Pulmonary vascular resistance was not altered by blocking Ang II, ET, or both but progressively increased during NO and PG blockade in group 2 (which had unblocked ET receptors), suggesting that endogenous ET exerts pulmonary vasoconstriction that is tempered by NO and PGs. In the kidney, blocking Ang II increased regional blood flow (RBF), glomerular filtration rate (GFR), and fractional excretion of sodium (FENa). In contrast, blocking ET did not alter RBF, and it decreased GFR and FENa. Combined Ang II and ET blockade markedly increased RBF without altering GFR, and FENa was maintained at the levels as when only ET was blocked. Sequentially inhibiting NO and PGs decreased RBF when Ang II or ET were blocked but had little effect when both were blocked. Finally, Ang II or ET blockade did not alter iliac blood flow. Inhibiting NO and PGs decreased iliac blood flow when Ang II or ET but not both were blocked. These results suggest that regional differences in the interactions between endogenous Ang II, ET, NO, and PGs are important determinants in systemic, pulmonary, and regional hemodynamics.

Subpressor doses of angiotensin II (SP-Ang II) cause a slow increase in blood pressure in rats as assessed by tail cuff plethysmography (TCP), reflecting either sustained hypertension or an exaggerated pressor response to diverse stimuli. We examined whether subpressor doses of Ang II enhance blood pressure responses to simple stress (handling of trained rats for TCP). We implanted telemetry in Sprague-Dawley rats. After 10 days of recovery and TCP training, we implanted osmotic minipumps with either SP-Ang II (50 ng/kg per minute) or vehicle, and then measured systolic blood pressure continuously in unrestrained rats for 13 days. We also recorded telemetry readings while obtaining TCP measurements every 2 days. SP-Ang II increased blood pressure from 134+/-19 to 159+/-22 mm Hg by TCP, which matched the simultaneous telemetry readings of 131+/-20 to 154+/-25 mm Hg. In contrast, SP-Ang II did not change the blood pressure in the unrestrained rats (measured with continuous telemetry: 124+/-2 versus 127+/-1 mm Hg). The blood pressure in the control rats did not change in the unrestrained state (125+/-3 versus 128+/-5 mm Hg on days 0 and 12, respectively), and only slightly increased during TCP (11+/-5 and 6+/-4 mm Hg by TCP and simultaneous telemetry, respectively; P=NS). In summary, SP-Ang II, although unable to provoke sustained hypertension, nonetheless magnifies the pressor response to otherwise trivial stimuli. We speculate that even modestly elevated Ang II levels may contribute to hypertensive complications because such levels promote the punctuation of an apparent normotensive state by episodic hypertension occasioned by seemingly innocuous stimuli.

Chronically infusing a subpressor dose of angiotensin (Ang) II increases blood pressure via poorly defined mechanisms. We found that this hypertensive response is accompanied by increased oxidant stress and is prevented by blocking endothelin (ET) receptors. Thus, we now tested whether blocking oxidant stress decreases both blood pressure and ET levels. We infused Sprague-Dawley rats (via osmotic pumps) with either vehicle (group 1) or Ang II (5 ng. kg(-1). min(-1); groups 2 to 4) for 15 days. Groups 3 and 4 also received either tempol in the drinking water (1 mmol/L) or vitamin E (5000 IU/kg diet), respectively, for 15 days. We measured systolic blood pressure (SBP) and urinary nitrite excretion every 3 days, and on day 15 we measured systemic and renal venous plasma levels of ET, isoprostanes, and thiobarbituric acid reactive substances (TBARS). SBP in Group 1 did not change throughout the study, whereas Ang II increased SBP (from 132+/-5 to 151+/-7 mm Hg). In addition, Ang II increased the systemic and renal venous levels of isoprostanes, TBARS, and ET and caused a transient decrease in urinary nitrites (that returned to control levels by day 9). Both tempol and vitamin E prevented Ang II-induced hypertension and either prevented or tended to blunt the increase in systemic and renal isoprostanes, TBARS, and ET. Finally, both antioxidants abolished the transient decrease in urinary nitrites. These results together with our previous study suggest that subpressor-dose Ang II increases oxidant stress (and isoprostanes). This in turn increases ET levels, which participate in the hypertensive response to Ang II.

We tested the hypothesis that angiotensin II (Ang II)-induced stimulations of endothelin (ET) and isoprostanes are implicated in the slow pressor responses to Ang II. We infused either vehicle (group 1) or Ang II (groups 2 to 4) intravenously at 5 ng/kg per minute via osmotic pumps for 15 days into Sprague-Dawley rats. Groups 3 and 4 received 30 mg/kg per day of either losartan (Ang II type 1 receptor blocker) or bosentan (ET(A) and ET(B) receptor blocker) in their drinking water. We measured systolic blood pressure (SBP) every 3 days during the infusion. Plasma levels of Ang II, ET, isoprostanes, and urinary nitrites were determined at 15 days. Vehicle infusion did not change SBP (from 138+/-13 to 136+/-2 mm Hg at day 15). Circulating Ang II, ET, and isoprostane levels were 35+/-9, 39+/-3, and 111+/-10 pg/mL, respectively, whereas urinary nitrites were 2.3+/-0.4 microgram/d. Ang II increased SBP (from 133+/-10 to 158+/-8 mm Hg), plasma Ang II (179+/-77 pg/mL), and isoprostanes (156+/-19 pg/mL) without altering ET levels (38+/-5 pg/mL) or urinary nitrites (1.8+/-0.5 microgram/d). Losartan prevented Ang II-induced increases in SBP and isoprostanes (SBP went from 137+/-5 to 120+/-4 mm Hg; isoprostanes were 115+/-15 pg/mL) while increasing urinary nitrite levels (5.2+/-1.1 microgram/d). Losartan did not alter Ang II (141+/-57 pg/mL) or ET (40+/-4 pg/mL) levels. Bosentan also blocked Ang II-induced hypertension (from 135+/-4 to 139+/-3 mm Hg) but did not decrease isoprostanes (146+/-14 pg/mL). Ang II (63+/-11 pg/mL), ET levels (46+/-2 pg/mL), and urinary nitrites (2.8+/-0.4 microgram/d) were not altered. In conclusion, our results suggest that low-dose Ang II increases isoprostanes via its Ang II type 1 receptor and causes an ET-dependent hypertension, without altering circulating ET levels.

Chronic intravenous infusion of subpressor doses of angiotensin II causes blood pressure to increase progressively over the course of several days. The mechanisms underlying this response, however, are poorly understood. Because high-dose angiotensin II increases oxidative stress, and some compounds that result from the increased oxidative stress (eg, isoprostanes) produce vasoconstriction and antinatriuresis, we tested the hypothesis that a subpressor dose of angiotensin II also increases oxidative stress, as measured by 8-epi-prostaglandin F(2alpha) (isoprostanes), which may contribute to the slow pressor response to angiotensin II. To test this hypothesis, we infused angiotensin II (10 ng/kg per minute for 28 days via an osmotic pump) into 6 conscious normotensive female pigs (30 to 35 kg). We recorded mean arterial pressure continuously with a telemetry system and measured plasma isoprostanes before starting the angiotensin II infusion (baseline) and again after 28 days with an enzyme immunoassay. Angiotensin II infusion significantly increased mean arterial pressure from 121+/-4 to 153+/-7 mm Hg (P<0. 05) without altering total plasma isoprostane levels (180.0+/-24.3 versus 147.0+/-29.2 pg/mL; P=NS). However, the plasma concentrations of free isoprostanes increased significantly, from 38.3+/-5.8 to 54.7+/-10.4 pg/mL (P<0.05). These results suggest that subpressor doses of angiotensin II increase oxidative stress, as implied by the increased concentration of free isoprostanes, which accompany the elevation in mean arterial pressure elevation. Thus, isoprostane-induced vasoconstriction and antinatriuresis may contribute to the hypertension induced by the slow pressor responses of angiotensin II.

Bradykinin plays an important role in the regulation of renal hemodynamics. However, there have been few studies of the effect of bradykinin on isolated afferent arterioles, vascular segments that are important for the regulation of renal blood flow and glomerular filtration rate. Our purpose was to study (1) the effects of bradykinin on isolated perfused rabbit afferent arterioles and (2) the mechanisms of actions. Afferent arterioles dissected from rabbits were perfused in vitro at 60 mm Hg. In afferent arterioles preconstricted with phenylephrine, 10(-12) to 10(-10) mol/L bradykinin increased luminal diameter from 9.0+/-1.0 to 14.3+/-1.2 microm (P<0.003). In contrast, 10(-9) and 10(-8) mol/L bradykinin decreased luminal diameter to 10.8+/-1.4 and 9.7+/-1.2 microm, respectively (P<0.001). Bradykinin added to the bath had no effect on preconstricted afferent arterioles. The addition of [des-Arg9]-bradykinin (10(-9) and 10(-8) mol/L), a B1 receptor agonist, to the lumen decreased diameter from 9.7+/-1.2 to 6.7+/-1.2 microm at 10(-8) mol/L (P<0.002). Icatibant (Hoe 140), a B2 receptor antagonist, blocked both the vasodilation and vasoconstriction induced by bradykinin as well as the vasoconstriction induced by [des-Arg9]-bradykinin. L-NAME had no effect on bradykinin-induced dilation or constriction. Indomethacin blocked both the dilation induced by 10(-12) to 10(-10) mol/L bradykinin and the constriction induced by 10(-9) to 10(-8) mol/L bradykinin. In fact, in the presence of indomethacin, 10(-9) and 10(-8) mol/L bradykinin increased luminal diameter from 6.2+/-0.7 to 10.7+/-0.6 microm at 10(-8) mol/L (P<0.001), which was attenuated by L-NAME. Finally, in the presence of SQ29548, a prostaglandin H2/thromboxane A2 receptor antagonist, bradykinin caused dilation at all concentrations tested. In conclusion, bradykinin has a biphasic effect on afferent arterioles. Both dilation and constriction may be mediated by bradykinin B2 receptors. The mechanisms of vasodilation and vasoconstriction are due to cyclooxygenase products, not nitric oxide.

While arterial hypertension and renal dysfunction are well recognized complications of renal irradiation, the mechanisms that trigger the development of these complications are unknown. Recently, it was reported that the endothelium is a major target in radiation injury. Because dysfunction of the endothelial cells may lead or contribute to the development of hypertension and renal dysfunction in radiation nephropathy, we tested the hypothesis that endothelium-dependent vasodilation is impaired in radiated kidneys prior to the onset of hypertension. To test this hypothesis, we used Long-Evans rats that had undergone left nephrectomy (3 weeks earlier) and irradiation (3000 r's) to the right kidney 8 days earlier (mean blood pressures in the irradiated rats were not different than in the controls). We then measured the changes in renal blood flow (RBF) induced by endothelium-dependent (acetylcholine and bradykinin) and -independent (nitroprusside, norepinephrine, and angiotensin II) vasoactive agents. We found that the increases in RBF induced by the endothelium-dependent but not independent vasodilators were markedly impaired in the irradiated kidneys. Blocking nitric oxide synthesis with nitro L-arginine methyl ester in sham rats mimicked the blunted responsiveness of the irradiated rats, whereas indomethacin (an inhibitor of prostaglandin synthesis) had no effect on either sham or irradiated rats. Finally, the RBF responses to the endothelium-independent vasoconstrictors, norepinephrine and angiotensin II, were not altered in the irradiated kidneys. These results suggest that renal irradiation causes endothelial dysfunction (prior to the onset of hypertension) but spares the vascular smooth muscle cells.

Studies of endothelial regulation of microvascular function have been hampered by the technical difficulty of removing the endothelium without damaging the vascular smooth muscle cells. This study presents a novel method of endothelial damage and lysis based on the facts that endothelial cells express specific antigens and that complement reacts with antibody/antigen complexes, causing cell lysis. We isolated and perfused rabbit glomerular afferent arterioles in vitro and examined vascular responses before and after treating them with an antibody against factor VIII-related antigen and complement. The treatment consisted of perfusing afferent arterioles with medium containing the antibody and complement for 10 minutes, followed by a 20-minute washout period. Before treatment, acetylcholine and the calcium ionophore A23187 (receptor- and nonreceptor-mediated endothelium-dependent vasodilators, respectively) dilated norepinephrine-preconstricted afferent arterioles, whereas neither dilated the arterioles after treatment, suggesting loss of endothelium-dependent vasodilation. In contrast, responses to nicardipine and norepinephrine (endothelium-independent vasodilator and constrictor, respectively) were not altered by the treatment, indicating intact vascular smooth muscle cell function. Transmission electron microscopy revealed that the antibody- and complement-treated arterioles had various degrees of endothelial damage, including areas of detachment from the basement membrane and marked loss of the number and structure of mitochondria, but no evidence of vascular smooth muscle cell damage. These results indicate that treatment with anti-factor VIII-related antigen antibody and complement is an effective method for eliminating endothelium-dependent vasodilation without altering endothelium-independent responses. Thus, this method may be useful for studying the functional role of the endothelium in microvessels.

Immunocytochemical studies have shown that renin, which is normally located in the juxtaglomerular afferent arteriole, may also be found farther upstream toward the interlobular artery during chronic stimulation of the renin-angiotensin system. We assessed the renin distribution along the renal microvasculature using both quantitative analysis and immunocytochemistry in rabbits that received a normal sodium diet (0.48% NaCl), a low sodium diet (0.04% NaCl), or enalapril (1 mg/kg/day) for 4 weeks. From the outer cortex we microdissected 1) the proximal portion of the afferent arteriole (p-AF) extending from the interlobular artery to a point 50 microns from the glomerulus, 2) the distal 50 microns including its intact terminus (d-AF), and 3) the glomerulus without the vascular pole (GL) and measured their renin content. In controls, renin was 0.3 +/- 0.2, 27.0 +/- 5.2, and 2.8 +/- 0.5 ng angiotensin I/hr/arteriole (or GL) in the p-AF, d-AF, and GL, respectively. The low sodium diet and enalapril increased renin in the d-AF (53.1 +/- 6.9 and 68.4 +/- 8.1, respectively) but not in the GL (3.3 +/- 1.0 and 3.6 +/- 0.7). In the p-AF, both caused a small increase (delta = 1.5); however, this increase was minuscule compared with the large increase in the d-AF (delta = 41).(ABSTRACT TRUNCATED AT 250 WORDS)

In uncomplicated essential hypertension, renal blood flow, glomerular filtration rate, and glomerular capillary pressure are within the normal range despite elevated renal perfusion pressure, suggesting abnormally high resistance of the preglomerular vessels. Among various preglomerular vascular segments, the afferent arteriole (Af-Art) is thought to be the site responsible for most resistance. However, little is known about the vascular reactivity of the Af-Art or its alteration in hypertension. In this study, we tested the hypothesis that pressure-induced constriction is exaggerated in Af-Arts from spontaneously hypertensive rats (SHRs). Single Af-Arts were microdissected from kidneys of SHRs and normotensive control Wistar-Kyoto (WKY) rats and were microperfused in vitro. When pressure in the Af-Art was increased stepwise from 20 to 80 mm Hg, luminal diameter increased similarly in both WKY and SHR Af-Arts (from 10.0 +/- 0.8 to 18.6 +/- 1.3 microns and from 10.1 +/- 1.2 to 16.9 +/- 1.5 microns, respectively). However, when pressure was further increased to 140 mm Hg, the diameter remained unchanged in WKY Af-Arts (19.2 +/- 1.9 microns), whereas it decreased significantly to 11.1 +/- 0.9 microns in those from SHRs. We conclude that pressure-induced constriction is exaggerated in SHR Af-Arts, which may contribute to the development and maintenance of hypertension.

Endothelin is a potent vasoconstrictor, whereas endothelium-derived relaxing factor (EDRF) is a potent vasodilator. Both are produced by the endothelium. Although they have been studied extensively in large vessels, little is known about their actions in renal microvessels. Using microdissected rabbit afferent arterioles, we studied the vascular response to synthetic endothelin and its interaction with EDRF and the effect of endothelin on renin release. Afferent arterioles were either microperfused in vitro at 60 mm Hg to measure luminal diameter or incubated without microperfusion to assess renin release. When added to the bath, 10(-10) or 10(-9) M endothelin decreased the diameter by 32 +/- 8% (n = 7, p less than 0.01) or 76 +/- 7% (p less than 0.0001), respectively. Pretreatment with Nw-nitro L-arginine, which inhibits synthesis of EDRF, decreased basal diameter by 15 +/- 1% (p less than 0.001) and augmented endothelin-induced constriction; decrease in diameter with 10(-10) M endothelin was 78 +/- 10% (n = 4, p less than 0.01 versus nontreated). In afferent arterioles preconstricted by endothelin, acetylcholine at concentrations of 10(-8) to 10(-5) M increased the diameter in a dose-dependent manner. Basal renin release was 0.62 +/- 0.15 ng angiotensin I/hr/afferent arterioles/hr (n = 13) and was not affected by endothelin (10(-10) to 10(-6) M). Increase in renin release by isoproterenol was the same in afferent arterioles pretreated with vehicle or endothelin (10(-7) M; delta, 0.49 +/- 0.21 versus 0.42 +/- 0.19; n = 13).(ABSTRACT TRUNCATED AT 250 WORDS)