Prostaglandins and nitric oxide in regional kidney blood flow responses to renal nerve stimulation

We examined the roles of cyclooxygenase products and of interactions between the cyclooxygenase and nitric oxide systems in the mechanisms underlying the relative insensitivity of medullary perfusion to renal nerve stimulation (RNS) in anaesthetized rabbits. To this end we examined the effects of ibuprofen and N^G-nitro-l-arginine (L-NNA), both alone and in combination, on the responses of regional kidney perfusion to RNS. Under control conditions, RNS produced frequency-dependent reductions in total renal blood flow (RBF; –82±3% at 6 Hz), cortical laser-Doppler flux (CLDF; –84±4% at 6 Hz) and, to a lesser extent, medullary laser-Doppler flux (MLDF; –46±7% at 6 Hz). Ibuprofen did not affect these responses significantly, suggesting that cyclooxygenase products have little net role in modulating renal vascular responses to RNS. L-NNA enhanced RBF (P=0.002), CLDF (P=0.03) and MLDF (P=0.03) responses to RNS. As we have shown previously, this effect of L-NNA was particularly prominent for MLDF at RNS frequencies 1.5 Hz. Subsequent administration of ibuprofen, in L-NNA-pretreated rabbits, did not affect responses to RNS significantly. We conclude that counter-regulatory actions of NO, but not of prostaglandins, partly underlie the relative insensitivity of medullary perfusion to renal nerve activation.     

Effects of ATP on rat renal haemodynamics and excretion: role of sodium intake, nitric oxide and cytochrome P450

Aim: Adenosine‐5′‐triphosphate (ATP) affects intrarenal vascular tone and tubular transport via P2 receptors; however, the actual role of the system in regulation of renal perfusion and excretion remains unclear and is the subject of this whole‐kidney study. Methods: Effects of suprarenal aortic ATP infusion, 0.6–1.2 mg kg⁻¹ h⁻¹, were examined in anaesthetised rats maintained on low‐ (LS) or high‐sodium (HS) diet. Renal artery blood flow (RBF, transonic flow probe) and the perfusion (laser‐Doppler flux) of the superficial cortex (CBF) and outer and inner medulla (OM–BF, IM–BF) were measured, together with sodium and water excretion and urine osmolality. Results: Adenosine‐5′‐triphosphate did not change arterial pressure, RBF or CBF while the effects on medullary perfusion depended on sodium intake. In LS rats ATP increased IM–BF 19 ± 6%, the effect was prevented by inhibition of nitric oxide (NO) with N‐nitro‐l ‐arginine methyl ester. In HS rats ATP decreased OM–BF 16 ± 3% and IM–BF (7 ± 4%, not significant); previous inhibition of cytochrome P450 with 1‐aminobenzotriazol blunted the OM–BF decrease and reversed the previous decrease of IM–BF to a 13 ± 8% increase. Inhibition of P2 receptors with pyridoxal derivative (PPADS) abolished medullary vascular responses to ATP. In HS rats pre‐treated with PPADS, ATP increased tubular reabsorption, probably via adenosine formation and stimulation of P1 receptors. Conclusion: The data indicate a potential role of ATP in the selective control of renal medullary perfusion, different in sodium depleted and sodium replete rats. The action of ATP appears to be mediated by the NO system and the cytochrome P450 dependent vasoactive metabolites.     

Renal nerve stimulation restores tubuloglomerular feedback after acute renal denervation

Renal nerves play an important role in the setting of the sensitivity of the tubuloglomerular feedback (TGF) mechanism. We recently reported a time-dependent resetting of TGF to a lower sensitivity 3–4 h after acute unilateral renal denervation (aDNX). This effect persisted after 1 week, but was then less pronounced. To determine whether normal TGF sensitivity could be restored in aDNX kidneys by low-frequency renal nerve stimulation (RNS), the following experiments were performed. Rats with aDNX were prepared for micropuncture. In one experimental group proximal tubular free flow (P_t) and stop flow pressures (P_sf) were measured during RNS at frequencies of 2, 4 and 6 Hz. In another series of experiments the TGF sensitivity was evaluated from the P_sf responses at different loop perfusion rates after 20 min of RNS at a frequency of 2 Hz. The maximal drop in P_sf (ΔP_sf) and the tubular flow rate at which half the maximal response in ΔP_sf was observed (turning point, TP), were recorded. At RNS frequencies of 2, 4 and 6 Hz, P_t decreased from the control level of 14.1 ± 0.8–13.1 ± 1.0, 12.4 ± 1.1 and 11.2 ± 0.8 mmHg (decrease 21%, P < 0.05), respectively, while at zero perfusion and during RNS at 2 and 4 Hz P_sf decreased from 42.5 ± 1.6 to 38.2 ± 1.4 and 32.8 ± 4.3 mmHg (decrease 23%, P < 0.05), respectively. The TGF characteristics were found to be reset from the normal sensitivity with TP of 19.0 ± 1.1 nL min^–1 and ΔP_sf of 8.7 ± 0.9 mmHg to TP of 28.3 ± 2.4 nL min^–1 (increase 49%, P < 0.05) and ΔP_sf of 5.8 ± 1.2 mmHg (decrease 33%) after aDNX. After 20 min of RNS at 2 Hz TP was normalized and ΔP_sf was 33% higher. Thus the present findings indicate that the resetting of the TGF sensitivity that occurred 2–3 h after aDNX could be partially restored by 20 min of RNS at a frequency of 2 Hz. These results imply that renal nerves have an important impact on the setting of the sensitivity of the TGF mechanism.     

GABA-site antagonism and pentobarbital actions do not depend on the alpha-subunit type in the recombinant rat GABA receptor

Aim: The roles of α‐subunits on the gamma‐aminobutyric acid (GABA)‐site antagonism and pentobarbital actions were examined in rat recombinant GABA_A receptors in Xenopus oocytes. Methods: Experiments were performed with binary and ternary GABA_A receptors containing α1‐, α4‐ or α5‐subunit by the two‐electrode voltage‐clamp technique. Results: The potency of GABA was significantly higher in the α1β2, α4β2 and α5β2 receptors compared with the α1β2γ2L, α4β2γ2L and α5β2γ2L receptors. However, the α5β2 receptor possessed significantly lower GABA efficacy compared with the α5β2γ2L receptor. While the γ2‐subunit was essential to the potency of GABA, its influence on the apparent GABA‐site antagonism was less profound. The antagonist affinity constants (K_B) of bicuculline inhibition and slopes of Schild plots were similar between all types of ternary and binary receptors except α5β2 receptor which was not tested. The pK_Bs and IC₅₀s of the GABA‐site antagonism were not significantly different between the α1β2γ2L, α4β2γ2L and α5β2γ2L receptors. Bicuculline blocked pentobarbital‐activated currents in a reversible and non‐competitive manner with the α1β2γ2L, α4β2γ2L, and α5β2γ2L receptors, indicating an allosteric inhibition of the GABA‐site. No significant difference of bicuculline potencies in inhibiting GABA‐ and pentobarbital‐activated currents was found between the α1β2γ2L, α4β2γ2L and α5β2γ2L receptors. Conclusion: The GABA‐site antagonism does not depend on the subtype of α‐subunits. Similarly, pentobarbital activates ternary receptors composed of different α‐subunits in a bicuculline‐sensitive manner. The potencies of bicuculline to inhibit pentobarbital‐activated currents are identical with receptors containing α1, α4 or α5‐subunit. The α1β2 and α4β2 receptors possess higher GABA potencies compared with the α1β2γ2L and α4β2γ2L receptors.     

Expression of oestrogen receptors alpha and beta during the period of uterine receptivity in rat: effect of ormeloxifene, a selective oestrogen receptor modulator

Aims: In the present study, we investigated expression, distribution and regulation of oestrogen receptors (ERs) α and β and their modulation by ormeloxifene (Orm) during the period of uterine receptivity in rat uterus in order to determine their role in endometrial sensitization. Methods: Uterine tissues of control and Orm‐treated (1.25 mg kg^?1, orally) rats were collected on days 3, 4, 5 morning and day 5 evening post‐coitum referring to non‐receptive, pre‐receptive and receptive phases respectively. mRNA and protein expression levels were determined by RT‐PCR and Western blot respectively. Immunohistochemical technique was used to localize the receptors. Results: RT‐PCR analysis revealed that ERα mRNA reached a peak level on day 5 morning whereas ERβ mRNA expression was found to be very low. In Orm‐treated rats, the ERα mRNA was suppressed at day 5. The protein expression of ERα increased after day 3 and that of ERβ remained very low throughout the pre‐implantation period; Orm caused a decrease in ERα on day 5 morning. In endometrium, ERα expression was regulated differentially in luminal epithelium, glandular epithelium and stroma. Orm caused a decrease in the percentage of ERα‐positive nuclei in all the three endometrial compartments on days 4 and 5, and the magnitude of reduction varied spatio‐temporally. In case of ERβ, immunostaining was not detectable in Orm‐treated and control groups. Conclusion: It appears that the complex uterine response to implantation is governed by differential cell‐specific ERα expression. The study suggested the inhibitory activity of Orm on ERα during the period of uterine receptivity.     

Effect of nitric oxide and renal nerves on renomedullary haemodynamics in SHR and Wistar rats,studied with laser Doppler technique

The threshold for activation of the humoral renal antihypertensive system, presumably residing in the renomedullary interstitial cells (RIC), is substantially reset upwards in the spontaneously hypertensive rat (SHR). Depressor reactions, normally elicited by an increased renal perfusion pressure, can be inhibited either by high frequency renal nerve stimulation or blockade of nitric oxide synthesis, i.e. manoeuvres decreasing renal blood flow at this high perfusion pressure. The present study was designed to explore the effects on regional renal haemodynamics of blocking NO synthesis with N-ω-nitro-l-arginine (l-NNA) in chloralose anaesthetized SHR and Wistar rats. Mean arterial blood pressure (MAP), heart rate (HR), renal blood flow (RBF), cortical blood perfusion (CBP) and papillary blood perfusion (PBP) were measured in renally innervated and denervated SHR (S_in=8, S_dn=8) and in Wistar rats (W_in=10, W_dn=10). An innervated non-treated Wistar group served as control (C_in=12). The laser Doppler technique was used to record CBP and PBP. MAP increased in all groups receiving l-NNA while HR, RBF and CBP simultaneously decreased. The relative decreases in RBF were more marked into the two SHR groups than in the corresponding Wistar groups. After l-NNA PBP also decreased in all four groups despite the increased MAP and more so in the S_i group; W_i -19±8 (P<0.05), W_d -17±6 (P=0.07), S_i -50±9 (P<0.01) and S_d-25±9% (P<0.05). We conclude that NO is important for maintaining PBP especially in SHR. The more marked decrease in PBP in the innervated SHR suggests a NO/renal nerve interaction in the control of renomedullary blood flow in SHR. This finding may be of importance for the regulation of the humoral renal depressor mechanism.     

Urinary excretion of prostaglandin F2α and 6-keto-prostaglandin F1α during volume expansion in man

Renal function and the urinary excretion of immunoreactive prostaglandin F_2α (PGF_2α) and 6-keto-prostaglandin F_1α (6-keto-PGF_1α) were investigated during volume expansion (VE) in 9 healthy young adults. The studies were started after at least 17 h of food and fluid deprivation. Volume expansion (3% of body weight) was achieved by a continuous infusion of Ringer's solution (0.22 ml/kg/min). This increased the urinary excretion of sodium from 195±25 to 714±55 μmol/min/1.73 m²(mean ± S.E.) and decreased the excretion of potassium by 24% and plasma renin activity by 60% (P<0.01). The clearance of inulin increased slightly (from 102.4±3.7 to 114.5±6.2 ml/min/1.73 m², P<0.025), whüe clearance of PAH did not change. The excretion of immunoreactive PGF_2α decreased in 8 out of 9 individuals during VE, from 1.58±0.15 to 0.97±0.10 ng/min/1.73 m²(P<0.01). In contrast, excretion of immunoreactive 6-keto-PGF_1α increased in 8 out of 9 subjects, from 2.32±0.20 to 3.47±0.48 ng/min/1.73 m²(P<0.05). Urinary excretion of PGF_2α and 6-keto-PGF_1α may reflect renal synthesis of prostaglandins (PGs) and prostacyclin (PGI₂), respectively. The results indicate that synthesis of PGs is decreased and that of PGI₂ is increased during VE in man. However, no simple relationship could be found between the prostaglandins and the renal functional parameters.     

Activation of renal pelvic chemoreceptors in rats: role of calcitonin gene-related peptide receptors

Substance P and calcitonin gene-related peptide (CGRP) increase afferent renal nerve activity (ARNA). A substance P receptor antagonist but not a CGRP receptor antagonist, h-CGRP (8–37), blocks the ARNA response to renal mechanoreceptor (MR) stimulation. We have examined whether calcitonin gene-related peptide activates renal pelvic sensory receptors and whether such activation contributes to renal chemoreceptor stimulation. The calcitonin gene-related peptide receptor antagonist, h-CGRP (8–37) [0.01–10 μmol L^?1] dose-dependently decreased (29 ± 4–86 ± 13%, P < 0.01) the ipsilateral afferent renal nerve activity in response to the renal pelvic administration of calcitonin gene-related peptide (0.26 μmol L^?1). Renal pelvic perfusion with 900 m M NaCl also increased ipsilateral ARNA (23 ± 3% increase, P < 0.02) and contralateral urinary sodium excretion (13 ± 4% increase, P < 0.05). However, these responses to hypertonic NaCl were unaltered by h-CGRP (8–37). Renal pelvic perfusion with 1 or 10 μM h-CGRP (8–37) also failed to alter the ARNA responses to KCl (31.25, 62.5 and 125 m M ). These results indicate that there are sensory receptors in the renal pelvic area that are responsive to calcitonin gene-related peptide. The activation of these receptors elicits a contralateral natriuretic response. In contrast, the activation of renal calcitonin gene-related peptide receptors does not contribute to renal chemoreceptor activation.     

Nitric oxide in responses of regional kidney perfusion to renal nerve stimulation and renal ischaemia

The mechanisms underlying the relative insensitivity of medullary blood flow (MBF) to sympathetic drive remain unknown. We tested the effects of nitric oxide synthase blockade on regional kidney perfusion responses to electrical renal nerve stimulation (RNS) in pentobarbitone-anaesthetized rabbits. Under control conditions, RNS reduced renal blood flow (RBF), cortical blood flow (CBF) and MBF in a frequency-dependent manner. MBF was always reduced less than CBF or RBF. N^G-nitro-l-arginine increased mean arterial pressure (31±3 mmHg), reduced RBF (–8±1 ml/min) and MBF (–33±6 units), enhanced responses to RNS of RBF (from –48±6% to –58±6% at 2 Hz), CBF (from –38±6% to –43±4% at 2 Hz) and, particularly at low frequencies, MBF (from +1±18% to –32±11% at 2 Hz) and potentiated the RBF hyperaemic response following RNS (by 27±6% at 4 Hz). When glyceryl trinitrate was co-infused with N^G-nitro-l-arginine to restore basal nitrergic tone, responses to RNS and the subsequent hyperaemia were indistinguishable from control. Since resting renovascular tone or perfusion pressure has little impact on MBF responses to RNS, these present observations suggest that NO contributes to the blunted MBF response to RNS. Paradoxically, NO seems to blunt renal hyperaemia following acute RNS-induced ischaemia.     

Interaction of gonadal steroids and the glucocorticoid corticosterone in the regulation of the L-type Ca(2+) current in rat left ventricular cardiomyocytes

Aim: Gonadal steroids as well as glucocorticoids have been shown to regulate the cardiac L‐type Ca²⁺ current (I_CaL). Herein, we compare the effects of the gonadal steroids testosterone and 17β‐estradiol with the glucocorticoid corticosterone on I_CaL, and investigate the interaction between the gonadal steroids and corticosterone. Methods: Myocytes were isolated from the left ventricular free wall of female and male Wistar rats and investigated using the ruptured‐patch whole‐cell patch‐clamp technique. Results: In myocytes isolated from female rats, 24 h incubation with 100 nm testosterone led to a 33% increase in I_CaL compared with control (?8.8 ± 0.5 pA pF^?1, n = 25 vs. ?6.6 ± 0.4 pA pF^?1, n = 26, P < 0.01, V_Pip = 0 mV). Incubation with 1 μm corticosterone resulted in a 79% increase in I_CaL (?11.8 ± 0.7 pA pF^?1, n = 29, P < 0.001). However, the combination of testosterone and corticosterone did not have any additional effect compared with corticosterone alone (?11.7 ± 0.6 pA pF^?1, n = 25, ns). In cardiomyocytes from male rats, I_CaL was not affected by testosterone, whereas the effect of corticosterone was preserved (P < 0.05). 24 h incubation with 17β‐estradiol increased I_CaL by 32% from ?7.6 ± 0.5 pA pF^?1 (n = 15) to 10.0 ± 0.9 pA pF^?1 (n = 15, P < 0.05). 17β‐estradiol did not exert an additional effect upon co‐incubation with corticosterone and did not have an effect on I_CaL in cardiomyocytes from female rats. Higher concentrations of the gonadal steroids did not result in increased effects. Conclusion: When compared with corticosterone, the in vitro effects of the gonadal steroids are small. However, under conditions in which I_CaL is not fully activated by glucocorticoids, gonadal steroids may significantly contribute to I_CaL regulation.     

The regulation of blood perfusion in the renal cortex and medulla by reactive oxygen species and nitric oxide in the anaesthetised rat

Aims: The regulation of blood flow through the renal medulla is important in determining blood pressure, and its dysregulation in pathophysiological states, such as oxidative stress, may contribute to the development of hypertension. This investigation examined the hypothesis that reactive oxygen species has both direct and indirect actions, via scavenging NO, to determine the degree of blood perfusion through the renal medulla. Methods: Groups of male Wistar rats received a renal interstitial infusion of either tempol, a superoxide dismutase (SOD) mimetic, or tempol plus catalase (tem + cat), or diethyldithio‐carbamic acid (DETC) a SOD inhibitor, or L‐NAME alone or L‐NAME followed by DETC. Results: Medullary blood perfusion (MBP) increased by 16 ± 1% (P < 0.05) following the renal infusion of tempol and by 35 ± 4%% (P < 0.05) when tem + cat was infused. Cortical blood perfusion (CBP) was unchanged during the administration of tempol and tem + cat. The renal interstitial infusion of DETC reduced CBP by 13 ± 2%, (P < 0.05) and MBP by 22 ± 3% (P < 0.05). Infusion of L‐NAME to block NOS did not change CBP but decreased MBP by 12 ± 4%, which was (P < 0.05) less than the reduction obtained with DETC. Administration of DETC in the presence of L‐NAME reduced CBP and MBP by 17 and 14%, respectively, the latter response being approximately half that obtained when only DETC was infused. Conclusions: These findings demonstrated that both reactive oxygen species and NO determined the level of MBP. The findings support the hypothesis that reactive oxygen species can act both indirectly, via scavenging of NO, and directly via H₂O₂ to modulate blood perfusion in the medulla.     

Enhanced beta-adrenergic response in rat papillary muscle by inhibition of inducible nitric oxide synthase after myocardial infarction

Aim: Myocardial infarction (MI) induces a progressive ventricular remodelling leading to a contractility depression. During the acute phase of MI inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production increases in the heart. The aim of this study was to investigate the role of iNOS in the left ventricular contractility at 3 days after MI. Methods: Wistar rats were divided into: sham operated (SHAM, n = 23), infarction (INF, n = 18); sham operated plus the iNOS inhibitor, S‐methylisothiourea (SMT) 5 mg kg^?1 day^?1, i.p. treatment (SHAM‐SMT, n = 26) and infarction plus SMT (INF‐SMT, n = 22). Concentration–response curves for isoprenaline, Ca²⁺ and frequency–force curve were studied in isolated papillary muscle from left ventricle. Results: After 3 days infarct area was similar between groups. SMT treatment reduced the time to peak tension during frequency–force curve in the infarct group (SHAM = 63 ± 3; SHAM‐SMT = 71 ± 3; INF = 90 ± 4; INF‐SMT = 79 ± 4 ms, P < 0.05) and increased the maximal response to isoprenaline (SHAM = 0.93 ± 0.11; SHAM‐SMT = 1.13 ± 0.1; INF =0.84 ± 0.16; INF‐SMT = 1.49 ± 0.15 g mm^?2, P < 0.05). The response to Ca²⁺ was equally reduced in the INF and INF‐SMT groups. SMT treatment did not change the reduced post‐rest potentiation performed by INF group, but attenuated the plasma nitrite and nitrate (NOx) levels in the INF group without any haemodynamic effect. Conclusion: These finding suggest that at 3 days after MI the iNOS modulates the isolated papillary muscle response to isoprenaline and its inhibition improves the β‐adrenergic inotropic responses.     

Renal endothelin system and excretory function in Wistar-Kyoto and Long-Evans rats

Aim: The role of the kidney endothelin system in the renal regulation of fluid and electrolyte excretion was investigated in Wistar–Kyoto (WKY) and Long–Evans (LE) rats in which we found previously marked differences in the renal excretory responses to endothelin A receptor blockade. Methods: The selective endothelin A and B receptor antagonists BQ‐123 (16.4 nmol kg⁻¹ min⁻¹) and BQ‐788 (25 nmol kg⁻¹ min⁻¹) were infused i.v. for 50 min in conscious chronically instrumented WKY and LE rats and their renal function and renal endothelin system were studied. Results: Without effects on glomerular filtration rate or renal blood flow, BQ‐123 and BQ‐788 decreased by more than 50% (P < 0.01) both urine flow rate and electrolyte excretion in WKY rats but only urine flow rate (P < 0.05) in LE rats. Endothelin‐1 content, preproET‐1/GPDH mRNA ratio, B_max and K_d of total endothelin receptors in renal cortex did not differ between the two strains. In contrast, plasma endothelin‐1 concentration (0.58 ± 0.04 vs. 1.05 ± 0.01 femtomol mL⁻¹; P < 0.01), renal papillary ET‐1 concentration (68 ± 5 vs. 478 ± 62 fmol mg⁻¹ protein; P < 0.01) and preproET‐1/GPDH mRNA ratio (0.65 ± 0.09 vs. 0.88 ± 0.05; P < 0.05) as well as total endothelin receptor number in renal papilla (B_max 5.3 ± 0.4 vs. and 9.0 ± 1.2 pmol mg⁻¹ protein; P < 0.05) were markedly lower in LE than in WKY rats. In vitro studies showed that in both strains ET_B receptors on renal cortical membranes amounted between 65% and 67% and on papillary membranes between 85% and 88%. Conclusion: The present data show that the selective ET_A or ET_B receptor blockade differentially affects tubular water and salt handling, which becomes apparent in conditions of low renal papillary endothelin receptor number and tissue endothelin‐1 concentration.     

AMPKα2 reduces renal epithelial transdifferentiation and inflammation after injury through interaction with CK2β

TGFβ1/Smad, Wnt/β‐catenin and snail1 are preferentially activated in renal tubular epithelia after injury, leading to epithelial–mesenchymal transition (EMT). The stress response is coupled to EMT and kidney injury; however, the underlying mechanism of the stress response in EMT remains elusive. AMP‐activated protein kinase (AMPK) signalling is responsive to stress and regulates cell energy balance and differentiation. We found that knockdown of AMPKα, especially AMPKα2, enhanced EMT by up‐regulating β‐catenin and Smad3 in vitro. AMPKα2 deficiency enhanced EMT and fibrosis in a murine unilateral ureteral obstruction (UUO) model. AMPKα2 deficiency also increased the expression of chemokines KC and MCP‐1, along with enhanced infiltration of inflammatory cells into the kidney after UUO. CK2β interacted physically with AMPKα and enhanced AMPKα Thr172 phosphorylation and its catalytic activity. Thus, activated AMPKα signalling suppresses EMT and secretion of chemokines in renal tubular epithelia through interaction with CK2β to attenuate renal injury. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Angiotensin II and renal prostaglandin release in the dog. Interactions in controlling renal blood flow and glomerular filtration rate

The relationship between angiotensin II and renal prostaglandins, and their interactions in controlling renal blood flow (RBF) and glomerular filtration rate (GFR) were investigated in 18 anaesthetized dogs with acutely denervated kidneys. Intrarenal angiotensin II infusion increased renal PGE₂ release (veno-arterial concentration difference times renal plasma flow) from 1.7 ± 0.9 to 9.1 ±0.4 and 6-keto-PGFja release from 0.1 ±0.1 to 5.3 ± 2.1 pmol min^-1. An angiotensin II induced reduction in RBF of 20% did not measurably change GFR whereas a 30% reduction reduced GFR by 18 ± 8%. Blockade of prostaglandin synthesis approximately doubled the vasocon-strictory action of angiotensin II, and all reductions in RBF were accompanied by parallel reductions in GFR. When prostaglandin release was stimulated by infusion of arachidonic acid (46.8± 13.3 and 15.9± 5.4 pmol min^-1 for PGE₂, and 6-keto-PGFja, respectively), angiotensin II did not change prostaglandin release, but had similar effects on the relationship between RBF and GFR as during control. In an ureteral occlusion model with stopped glomerular filtration measurements of ureteral pressure and intrarenal venous pressure permitted calculations of afferent and efferent vascular resistances. Until RBF was reduced by 25–30% angiotensin II increased both afferent and efferent resistances almost equally, keeping the ureteral pressure constant. At greater reductions in RBF, afferent resistance increased more than the efferent leading to reductions in ureteral pressure. This pattern was not changed by blockade of prostaglandin synthesis indicating no influence of prostaglandins on the distribution of afferent and efferent vascular resistances during angiotensin II infusion. In this ureteral occlusion model glomerular effects of angiotensin II will not be detected, and it might well be that the shift from an effect predominantly on RBF to a combined effect on both RBF and GFR induced by inhibition of prostaglandin synthesis is located to the glomerulus. We therefore postulate that renal prostaglandins attenuate the effects of angiotensin II on glomerular surface area and the filtration barrier, and not on the afferent arterioles as previously suggested.     

Nitric oxide, superoxide and renal blood flow autoregulation in SHR after perinatal L-arginine and antioxidants

Aim: Nitric oxide (NO) and superoxide are considered to be regulatory in renal blood flow (RBF) autoregulation, and hence may contribute to development of hypertension. To extend our previous observations that dynamic NO release is impaired in the spontaneously hypertensive rat (SHR) we investigated, firstly, if superoxide dependency of RBF autoregulation is increased in SHR and, secondly, if the beneficial effect of perinatal supplementation in SHR is partly as a result of early correction of RBF autoregulation. We hypothesized that perinatal supplementation by restoring dynamic NO release and/or decreasing superoxide dependency and would improve life‐long blood pressure regulation. Methods: Autoregulation was studied using stepwise reductions in renal perfusion pressure in anaesthetized male SHR, SHR perinatally supplemented with arginine and antioxidants (SHRsuppl) and Wistar‐Kyoto (WKY), prior to and during i.v. Nω‐nitro‐l ‐arginine (NO synthase inhibitor) or tempol (superoxide dismutase mimetic). Results: Spontaneously hypertensive rat displayed a wider operating range of RBF autoregulation as compared with WKY (59 ± 4 vs. 33 ± 2 mmHg, respectively; P < 0.01). Perinatal supplementation in SHR decreased mean arterial pressure, renal vascular resistance and the operating range of RBF autoregulation (43 ± 3 mmHg; P < 0.01). In addition autoregulation efficiency decreased. RBF autoregulation characteristics shifted towards those of normotensive WKY. However, dynamic NO release was still impaired and no clear differences in superoxide dependency in RBF autoregulation between groups was observed. Conclusion: Perinatal supplements shifted RBF autoregulation characteristics of SHR towards WKY, although capacity of the SHRsuppl kidney to modulate NO production to shear stress still seems impaired. The less strictly controlled RBF as observed in perinatally supplemented SHR could result in an improved long‐term blood pressure control. This might partly underlie the beneficial effects of perinatal supplementation.     

Renal arterial infusion of tempol prevents medullary hypoperfusion,hypoxia, and acute kidney injury in ovine Gram-negative sepsis

Aim

Renal medullary hypoperfusion and hypoxia precede acute kidney injury (AKI) in ovine sepsis. Oxidative/nitrosative stress, inflammation, and impaired nitric oxide generation may contribute to such pathophysiology. We tested whether the antioxidant and anti-inflammatory drug, tempol, may modify these responses.

Methods

Following unilateral nephrectomy, we inserted renal arterial catheters and laser-Doppler/oxygen-sensing probes in the renal cortex and medulla. Noanesthetized sheep were administered intravenous (IV) Escherichia coli and, at sepsis onset, IV tempol (IVT; 30 mg kg⁻¹ h⁻¹), renal arterial tempol (RAT; 3 mg kg⁻¹ h⁻¹), or vehicle.

Results

Septic sheep receiving vehicle developed renal medullary hypoperfusion (76 ± 16% decrease in perfusion), hypoxia (70 ± 13% decrease in oxygenation), and AKI (87 ± 8% decrease in creatinine clearance) with similar changes during IVT. However, RAT preserved medullary perfusion (1072 ± 307 to 1005 ± 271 units), oxygenation (46 ± 8 to 43 ± 6 mmHg), and creatinine clearance (61 ± 10 to 66 ± 20 mL min⁻¹). Plasma, renal medullary, and cortical tissue malonaldehyde and medullary 3-nitrotyrosine decreased significantly with sepsis but were unaffected by IVT or RAT. Consistent with decreased oxidative/nitrosative stress markers, cortical and medullary nuclear factor-erythroid-related factor-2 increased significantly and were unaffected by IVT or RAT. However, RAT prevented sepsis-induced overexpression of cortical tissue tumor necrosis factor alpha (TNF-α; 51 ± 16% decrease; p = 0.003) and medullary Thr-495 phosphorylation of endothelial nitric oxide synthase (eNOS; 63 ± 18% decrease; p = 0.015).

Conclusions

In ovine Gram-negative sepsis, renal arterial infusion of tempol prevented renal medullary hypoperfusion and hypoxia and AKI and decreased TNF-α expression and uncoupling of eNOS. However, it did not affect markers of oxidative/nitrosative stress, which were significantly decreased by Gram-negative sepsis.     

Intrarenal administration of angiotensin II does not moderate afferent renal nerve mediated cardiovascular reflexes in the anaesthetized rabbit

Stimulation of the afferent renal nerves in the anaesthetized rabbit by acute reduction in renal perfusion pressure results in a neurally mediated, reflex increase in hindlimb vascular resistance. To determine whether exogenous angiotensin II moderates the reflex, the kidneys of anaesthetized rabbits were vascularly isolated and renal blood flow was occluded acutely, following intrarenal administration of vehicle (0.9% saline) or angiotensin II (0.5 ng), and the hindlimb vascular response was measured. Occlusion of renal blood flow resulted in similar, significant increases in femoral perfusion pressure of 39.7±7.1 mmHg after vehicle and 21.3±8.9 mmHg (P<0.05, n=6) after angiotensin II. The viability of the preparation following repeated episodes of renal blood flow occlusion was tested by a series of three rapid (2–3 min delay) occlusions and three delayed (30 min delay) occlusions. Femoral perfusion pressure rose by 43.1±10.7 mmHg (rapid, P<0.05, n=11) and 64.4±12.3 mmHg (delayed, P<0.05, n = 5) on the first occasion. On the second occasion, the rapid occlusion did not result in a significant increase in femoral perfusion pressure (29.1±8.1 mmHg), but the delayed group did (54.6±22.4 mmHg, P<0.05). On the third occasion, neither group showed a significant change (20.9±16.3 and 30.8±13.5 mmHg). These data suggest that exogenous angiotensin II does not moderate the afferent renal nerve reflex. The decline in hindlimb response following rapid serial occlusion may be attributed to a diminution of an intermediary substance(s) at the nerve receptor site.     

Mechanisms of K(+) induced renal vasodilation in normo- and hypertensive rats in vivo

Aim: We investigated the mechanisms behind K⁺‐induced renal vasodilation in vivo in normotensive Sprague–Dawley (SD) rats and spontaneously hypertensive rats (SHR). Methods: Renal blood flow (RBF) was measured utilizing an ultrasonic Doppler flow probe. Renal vascular resistance (RVR) was calculated as the ratio of mean arterial pressure (MAP) and RBF (RVR = MAP/RBF). Test drugs were introduced directly into the renal artery. Inward rectifier K⁺ (K_ir) channels and Na⁺,K⁺‐ATPase were blocked by Ba²⁺ and ouabain (estimated plasma concentrations ～20 and ～7 μm ) respectively. Results: Confocal immunofluorescence microscopy demonstrated K_ir 2.1 channels in pre‐glomerular vessels of SD and SHR. Ba²⁺ caused a transient (6–13%) increase in baseline RVR in both SD and SHR. Ouabain had a similar effect. Elevated renal plasma [K⁺] (～12 mm ) caused a small and sustained decrease (5–13%) in RVR in both strains. This decrease was significantly larger in SHR than in SD. The K⁺‐induced vasodilation was attenuated by Ba²⁺ in control SD and SHR and by ouabain in SD. Nitric oxide (NO) blockade using l ‐NAME treatment increased MAP and decreased RBF in both rat strains, but did not affect the K⁺‐induced renal vasodilation. Conclusion: K⁺‐induced renal vasodilation is larger in SHR, mediated by K_ir channels in SD and SHR, and in addition, by Na⁺,K⁺‐ATPase in SD. In addition, NO is not essential for K⁺‐induced renal vasodilation.     

Inhibitory effect of endothelin on renin release in dog kidneys

To investigate the effect of endothelin on renin release, experiments were performed in barbiturate-anaesthetized dogs with denervated kidneys. Intrarenal infusion of endothelin (1 ng min^-1kg^-1body wt) reduced renal blood flow (RBF) from 145 ± 10 ml min^-1to 98 ± 9 ml min^-1without altering renin release (1 ± 1 μg angiotensin I (AI) min^-1). Renin release was then increased either by renal arterial constriction or ureteral occlusion. When renal arterial pressure was reduced to 50 mmHg, renin release averaged 79 ± 20 μg AI min^-1in six dogs and fell significantly to 24 ± 6 μg AI min^-1during endothelin infusion. During ureteral occlusion the inhibitory effect of endothelin on renin release either during inhibition of β-adrenergic activity with propranolol or after inhibiting prostaglandin synthesis by indomethacin during intrarenal infusion of isoproterenol was examined. After propranolol administration ureteral occlusion increased renin release from 5 ± 2 μg AI min^-1to 38 ± 12 μg AI min^-1in six dogs. Subsequent intrarenal endothelin infusion (1 ng min^-1kg^-1body wt) during maintained ureteral occlusion reduced renin release to 10 ± 3 μg AI min^-1. In six other dogs prostaglandin synthesis was inhibited by indomethacin. Subsequent infusion of isoproterenol (0.2 μg min^-1kg^-1body wt) to stimulate β-adrenoceptor activity increased renin release from 13 ± 4 μg AI min^-1to 68 ± 8 μg AI min^-1during ureteral occlusion. Intrarenal endothelin infusion (1 ng min^-1kg^-1body wt) reduced renin release to 22 ± 3 μg AI min^-1during continuous isoproterenol infusion and ureteral occlusion. Hence endothelin inhibits renin release induced by renal arterial constriction or ureteral occlusion. Similar inhibitory effects whether renin release was raised by increasing prostaglandin synthesis or by stimulating β-adrenergic activity suggest a direct effect of endothelin on the juxtaglomerular cells.