Nationwide surveillance of antimicrobial consumption and resistance to Pseudomonas aeruginosa isolates at 203 Japanese hospitals in 2010.

PURPOSE: In Japan, a national surveillance study of antimicrobial consumption has never been undertaken. This study aimed to describe antimicrobial consumption and resistance to Pseudomonas aeruginosa in 203 Japanese hospitals, to identify targets for quality improvement. METHODS: We conducted an ecological study using retrospective data (2010). Antimicrobial consumption was collected in the World Health Organization (WHO) anatomical therapeutic chemical/defined daily dose (ATC/DDD) format. Rates of imipenem (IPM), meropenem (MEPM), ciprofloxacin (CPFX), or amikacin (AMK) resistance were expressed as the incidence of non-susceptible isolates. Additionally, hospitals were asked to provide data concerning hospital characteristics and infection control policies. Hospitals were classified according to functional categories of the Medical Services Act in Japan. RESULTS: Data were collected from 203 Japanese hospitals (a total of 91,147 beds). The total antimicrobial consumption was 15.49 DDDs/100 bed-days (median), with consumptions for penicillins, carbapenems, quinolones, and glycopeptides being 4.27, 1.60, 0.41, and 0.49, respectively. The median incidences of IPM, MEPM, CPFX, and AMK resistance were 0.15, 0.10, 0.13, and 0.03 isolates per 1,000 patient-days, respectively. Antimicrobial notification and/or approval systems were present in 183 hospitals (90.1 %). In the multivariate analysis, the piperacillin/tazobactam, quinolones, and/or total consumptions and the advanced treatment hospitals showed a significant association with the incidence of P. aeruginosa resistant to IPM, MEPM, CPFX, and AMK [adjusted R (2) (aR (2)) values of 0.23, 0.30, 0.22, and 0.35, respectively). CONCLUSION: This is the first national surveillance study of antimicrobial consumption in Japan. A continuous surveillance program in Japan is necessary in order to evaluate the association among resistance, antimicrobial restriction, and consumption.

Abnormal expression and function of Fas ligand of lacrimal glands and peripheral blood in Sjögren's syndrome patients with enlarged exocrine glands.

The objective of our study was to investigate the possibility of Fas ligand protein abnormalities in certain types of Sjögren's syndrome patients with enlarged exocrine glands. Fas ligand expression by lymphocytes infiltrating the lacrimal glands and by peripheral blood monocytes in Sjögren's syndrome patients with enlarged exocrine glands was assessed immunohistologically and by immunoblotting. Cytotoxicity of peripheral blood monocytes and sensitivity to steroids in Sjögren's syndrome patients with enlarged exocrine glands were studied by functional assay. Minimal Fas ligand expression was detected in the lymphocytes of the lacrimal glands and a decreased level of Fas ligand was found in peripheral blood monocytes as assessed by immunoblotting. Functional assay confirmed the decreased cytotoxicity of lymphocytes in Sjögren's syndrome patients with enlarged exocrine glands, and that it is not affected by anti-Fas ligand antibody. By contrast, the sensitivity of lymphocytes in Sjögren's syndrome patients with enlarged exocrine glands to steroids was increased. These observations suggest that abnormal expression and function of Fas ligand occurs in Sjögren's syndrome patients with enlarged exocrine glands.

1,25-Dihydroxyvitamin D3 promotes vitamin K2 metabolism in human osteoblasts.

It has been reported that vitamin K2 (menaquinone-4) promoted 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-induced mineralization and enhanced gamma-carboxyglutamic acid (Gla)-containing osteocalcin accumulation in cultured human osteoblasts. In the present study, we investigated whether menaquinone-4 (MK-4) was metabolized in human osteoblasts to act as a cofactor of gamma-glutamyl carboxylase. Both conversions of MK-4 to MK-4 2,3-epoxide (epoxide) and epoxide to MK-4 were observed in cell extracts of cultured human osteoblasts. The effect of 1,25(OH)2D3 and warfarin on the vitamin K cycle to cultured osteoblasts were examined. With the addition of 1 nM 1,25(OH)2D3 or 25 microM warfarin in cultured osteoblasts, the yield of epoxide from MK-4 increased. However, the conversion of epoxide to MK-4 was strongly inhibited by the addition of warfarin (2.5-25 microM), whereas it was almost not inhibited by 1,25(OH)2D3 (0.1-10 nM). To clarify the mechanism for this phenomenon, a cell-free assay system was studied. Osteoblast microsomes were incubated with 10 microM epoxide in the presence or absence of warfarin and 1,25(OH)2D3. Epoxide reductase, one of the enzymes in the vitamin K cycle was strongly inhibited by warfarin (2.5-25 microM), whereas it was not affected by 1,25(OH)2D3 (0.1-1 nM). Moreover, there was no effect of pretreatment of osteoblasts with 1 nM 1,25(OH)2D3 on the activity of epoxide reductase. However, the activity of epoxidase, that is the gamma-glutamyl carboxylase was induced by the pretreatment of osteoblasts with 1 nM 1,25(OH)2D3. In the present study, it was demonstrated that the vitamin K metabolic cycle functions in human osteoblasts as well as in the liver, the post-translational mechanism, by which 1,25(OH)2D3 caused mineralization in cooperation with vitamin K2 was clarified.

Highly diastereoselective 1,4-addition of an organocuprate to methyl alpha-D-gluco-, alpha-D-manno-, or alpha-D-galactopyranosides tethering an alpha,beta-unsaturated ester. Novel asymmetric access to beta-C-substituted butanoic acids.

The 1,4-addition of magnesium divinylcuprate prepared from vinylmagnesium bromide and cuprous bromide to some 4-O-crotonyl derivatives of methyl alpha-D-glucopyranoside proceeds with a high level of diastereochemical induction, providing the adduct in good-to-excellent yields. Other organocuprates also serve as effective carbon nucleophiles for the 1,4-addition. Removal of the carbohydrate moiety from each adduct afforded a variety of beta-C-substituted butanoic esters in remarkable enantiomeric excess. The 1,4-addition of the same cuprate to some methyl alpha-D-manno- or alpha-D-galactopyranosidic substrates in which a crotonyl group was incorporated, each at 3-OH, was also investigated. The reverse pi-facial attack of the cuprate was observed when some D-manno-type substrates were subjected to 1,4-addition conditions similar to those used for the D-gluco-type substrates. Furthermore, some D-galacto-type substrates provided 1,4-adducts with higher diastereoselectivities.

Synthetic study of macquarimicins: highly stereoselective construction of the AB-ring system.

The highly stereoselective synthesis of the AB-ring system of macquarimicins, a novel class of microbial metabolites with inhibitory activity for neutral sphingomyelinase, has been achieved. The present synthesis features the highly stereocontrolled construction of the cis-tetrahydroindan structure via the intramolecular Diels-Alder reaction of an (E,Z,E)-1,6,8-nonatriene derived from D-glyceraldehyde acetonide. Reaction: see text.

Pathophysiological roles of endogenous endothelin-1 in dogs with chronic heart failure produced by rapid right ventricular pacing.

This study was designed to analyze the pathophysiological role of the endogenous endothelin (ET) system and the therapeutic approach to congestive heart failure (CHF) with ET(A)/ET(B) receptor antagonists in a canine CHF model. After 3 weeks of rapid right ventricular pacing (240 beats/min), concentrations of immunoreactive ET-1 in dogs increased approximately 2-fold in plasma and in the left and right ventricles but not in the lung. There were no meaningful changes in the density and affinity of total ET receptors, or in the ratio of ET(A) to ET(B) receptors. To clarify the functional role of endogenous ET, we examined the effects of acute injection of J-104132 (1 and 3 mg/kg i.v.), an ET(A)/ET(B) receptor antagonist, on cardiovascular and renal function in dogs with CHF. Compared with vehicle, J-104132 at both doses significantly decreased pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), and mean arterial pressure (MAP), and increased cardiac output (CO) and renal blood flow. J-104132 had no effects on heart rate and cardiac contractility. In addition, we examined whether J-104132 has an additive effect in the presence of enalaprilat. J-104132 (1 mg/kg i.v.) administered after enalaprilat (0.05 mg/kg i.v.) induced further decreases in MAP, PCWP and PAP, and further increases in CO, resulting in further decreases in total peripheral resistance. These results indicate that the endogenous ET system is exaggerated in CHF and has a detrimental effect on cardiac function. Therefore, J-104132 given alone or as combination therapy may play a beneficial role in the treatment of CHF in humans.

Effects of bradykinin on renal nerve stimulation-induced antidiuresis and norepinephrine overflow in anesthetized dogs.

We examined effects of bradykinin on antidiuresis and norepinephrine overflow induced by renal nerve stimulation (RNS) in anesthetized dogs, with or without blockade of the B2 receptor by Hoe 140 (D-Arg-[Hyp3, Thi5, D-Tic7, Oic8]bradykinin) or the endogenous nitric oxide generation by N(G)nitro-L-arginine (NOARG), a nitric oxide synthase inhibitor. RNS (0.5-2.0 Hz) produced significant decreases in urine flow, urinary and fractional excretions of sodium, and increases in norepinephrine secretion rate (NESR), without affecting systemic and renal hemodynamics. Intrarenal arterial infusion of bradykinin (5 ng/kg per minute) significantly suppressed the RNS-induced antidiuresis and increase in NESR. Hoe 140 (100 ng/kg per minute) did not affect the RNS-induced renal actions, but in the presence of Hoe 140, bradykinin-induced suppressive actions on reductions in urine formation and increases in NESR in response to RNS were abolished. RNS during intrarenal arterial infusion of NOARG (40 microg/kg per minute) led to potent reductions in urine formation and decreased renal blood flow and glomerular filtration rate. Simultaneously, NESR was markedly increased. During NOARG infusion, bradykinin-induced decreases in renal actions elicited by RNS were markedly attenuated. These findings suggest that bradykinin suppresses the RNS-induced norepinephrine overflow and renal actions via nitric oxide production mediated by activation of B2 receptor. Renal noradrenergic neurotransmission may be inhibited by bradykinin at the prejunctional level, when its local production in the kidney is enhanced.

Improvement of lacrimal function by topical application of CyA in murine models of Sjögren's syndrome.

PURPOSE: The object of this study was to evaluate improvement of lacrimal gland (LG) function after topical cyclosporin A (CyA). METHODS: Topical CyA (0.01% and 0.1%) was applied to two mouse models of Sjögren's syndrome, the NFS/sld after thymectomy and the nonobese diabetic (NOD) mouse, and the functional integrity of the lacrimal gland was evaluated by measuring basal and stimulated tear secretion and its histologic integrity by examining it for apoptosis and lymphocyte invasion. RESULTS: After treatment with CyA at 0.1% in the NFS/sld mice, tear function increased, and there was a decrease in lymphocyte infiltration of the LG and a decrease in apoptotic figures among the acinar cells. In the NOD mice, tear function also improved, but there was no associated decrease in lymphocyte infiltration. However, the expression of Fas ligand (FasL) in NOD mice by infiltrating lymphocytes was suppressed with 0. 1% CyA eye drops. CONCLUSIONS: CyA appears to improve tear secretion in mouse models of Sjögren's syndrome by preventing lymphocyte-induced apoptosis of acinar cells. In one model this was achieved by preventing lymphocyte infiltration and in the other by reducing expression of FasL expression on infiltrating lymphocytes.

Syntheses and absolute stereochemistries of UPA0043 and UPA0044, cytotoxic antibiotics having a p-quinone-methide structure.

The first syntheses of new antibiotics UPA0043 and UPA0044 were accomplished starting from commercially available 18beta-glycyrrhetinic acid and vanillin. The present syntheses involve the coupling of a sesquiterpenoid aldehyde and an aryllithium, the stereoselective formation of a p-quinone-methide system, and regioselective intramolecular cyclization via an epoxy ring opening. [reaction: see text]

Total synthesis of (-)-mniopetal E, a novel biologically intriguing drimane sesquiterpenoid.

We have achieved the total synthesis of (-)-mniopetal E, a drimane sesquiterpenoid which inhibits the reverse transcriptase of human immunodeficiency virus (HIV)-1. Our enantiospecific total synthesis of this target molecule in naturally occurring form commenced with a known 2,3-anhydro-D-arabinitol derivative, which was prepared using the Sharpless asymmetric epoxidation strategy. The key steps of our total synthesis were as follows: (1) a combination of highly stereocontrolled inter- and intramolecular Horner-Emmons carbon elongations for construction of a butenolide tethering a 1,2,4, 9-functionalized nona-5,7-diene moiety at the beta-carbon, (2) stereoselective thermal intramolecular Diels-Alder reaction of the thus-formed trienic compound, providing preferentially an endo-cycloadduct with the desired pi-facial selection, and (3) efficient transformation of the gamma-lactone moiety in the major cycloadduct to the gamma-hydroxy-gamma-lactone part in mniopetal E. Our total synthesis of (-)-mniopetal E established the unsettled absolute stereochemistry of the antibiotic.

Renal haemodynamic and excretory responses to bradykinin in anaesthetized dogs.

1. Effects of bradykinin (BK) on renal haemodynamics and urine formation were examined in anaesthetized dogs. 2. Renal arterial infusion of BK at doses of 5 or 50 ng/kg per min produced dose-dependent increases in renal blood flow (RBF), without affecting systemic arterial pressure or glomerular filtration rate. There were also significant and dose-dependent increases in urine flow (UF), urinary excretion of sodium (UNaV) and fractional excretion of sodium (FENa) and decreases in urine osmolality during BK infusion. 3. Renal haemodynamic and excretory responses to the BK infusion were completely abolished by the simultaneous administration of Hoe 140 (icatibant, 100 ng/kg per min intrarenally), a selective BK B2-receptor antagonist. 4. In the presence of NG-nitro-L-arginine (NOARG; 40 micrograms/kg per min intrarenally), a nitric oxide (NO) synthase inhibitor, BK-induced renal vasodilative and natriuretic effects were markedly attenuated, although responses of UF and urine osmolality to BK remained unchanged. The water diuretic effect of BK was abolished in dogs given both NOARG and ibuprofen (12.5 mg/kg bolus injection plus 12.5 mg/kg per h of sustained infusion intravenously), a cyclooxygenase inhibitor. 5. These results clearly indicate that renal haemodynamic and excretory responses to BK were mediated exclusively by the B2-receptor. Renal vasodilative and natriuretic responses are mainly linked to NO generation, while both NO and prostaglandin biosynthesis are involved in the BK-induced water diuresis.

Inhibitory effects of proadrenomedullin N-terminal 20 peptide on antidiuresis and norepinephrine overflow induced by stimulation of renal nerves in anesthetized dogs.

The effects of proadrenomedullin N-terminal 20 peptide (PAMP) on changes in renal function and norepinephrine (NE) overflow induced by renal nerve stimulation (RNS) were examined in anesthetized dogs. The intrarenal arterial infusion of PAMP (10, 50, 100 ng/kg/min) did not influence basal levels of systemic and renal hemodynamics, or urine formation. RNS at a low frequency (0.5-2.0 Hz) caused significant decreases in urine flow and urinary excretion of sodium, and increases in NE secretion rate (NESR), without affecting renal hemodynamics. RNS at a high frequency (2.5-5.0 Hz), which diminishes renal hemodynamics, elicited more potent decreases in urine formation and increases in NESR. The low frequency RNS-induced reductions in urine formation and increases in NESR were almost completely abolished by the intrarenal arterial infusion of PAMP at 50 ng/kg/min, a dose that produced no alterations on basal renal hemodynamics and excretory responses. In contrast, high frequency RNS-induced renal vasoconstriction and reductions in urine formation, and increases in NESR were not affected by infusion of the peptide. We next examined the effect of PAMP on exogenously applied NE-induced renal actions, to determine if PAMP functions suppressively at postjunctional sites. The intrarenal arterial infusion of NE (100-150 ng/kg/min) produced a significant renal vasoconstriction and a reduction in urine formation, responses not affected by the administration of PAMP (50 ng/kg/min). From these findings, we suggest that PAMP functions as an inhibitory modulator of renal noradrenergic neurotransmission, via prejunctional mechanisms, and plays an important role in regulating renal functions.

Changes in the enzymatic activities of beagle liver during maturation as assessed both in vitro and in vivo.

1. We have examined changes in caffeine and trimethadione (TMO) metabolism in vivo, agents which are used as probe drugs. In this study the total body clearance (Cl) of caffeine and TMO was low 1 week after birth (week 1), increased rapidly from week 3, peaked and then decreased gradually until reaching the level for the mature, adult dog. The elimination half-life (t1/2) of caffeine and TMO was prolonged during week 1; however, it then gradually became shorter. Gradually it became longer and reached the level for the adult dog. The apparent volume of distribution (Vd) of caffeine did not change throughout the study. However, the Vd of TMO was only high during week 1. 2. The in vitro changes in a variety of typical substrates for seven different cytochrome P450 (CYP) isozymes were examined. In this study three different patterns of metabolism can be identified: (1) activity is low immediately after birth, increases, peaks and then decreases to the adult dog level (p-nitroanisole; CYP1A1, caffeine; CYP1A2, benzphetamine; CYP3A/2B(?), aniline; 2E1 and TMO; CYP2C9/2E1/3A4); (2) activity generally increases rapidly soon after birth, continues to increase, peaks and then gradually decreases to the adult level (phenytoin; CYP2C9); and (3) activity is high (about the same level as the adult) immediately after birth, decreases and then gradually increases to the adult level (erythromycin; CYP3A4/5). 3. The results of these in vivo and in vitro studies suggest that changes in enzyme activity are due to differences in P450 isoenzymes during development.

Effects of FK409, a nitric oxide donor, on renal responses to renal nerve stimulation in anesthetized dogs.

We examined the effects of (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409), a nitric oxide (NO) donor, on renal actions and norepinephrine overflow induced by renal nerve stimulation in anesthetized dogs, with or without N(G)-nitro-L-arginine (NOARG), a NO synthase inhibitor. Renal nerve stimulation at a low frequency (0.5-2.0 Hz) produced significant decreases in urine flow and urinary excretion of Na+ and increases in norepinephrine secretion rate. Renal nerve stimulation at a high frequency (2.5-5.0 Hz) which diminishes renal hemodynamics, elicited more marked decreases in urine formation and increases in norepinephrine secretion rate. Intrarenal arterial infusion of FK409 (0.25 microg/kg/min) failed to alter renal actions and increases in norepinephrine secretion rate in response to both low- and high frequency renal nerve stimulation. When NOARG (40 microg/kg/min) was administrated intrarenally, low-frequency renal nerve stimulation caused a potent antidiuresis and renal vasoconstriction. The renal nerve stimulation-induced increase in norepinephrine secretion rate was markedly enhanced by NOARG infusion. Simultaneous infusion of FK409 markedly attenuated the NOARG-induced enhancement of renal actions and increases in norepinephrine secretion rate, in response to low-frequency renal nerve stimulation. These results suggest that exogenous NO suppresses the renal nerve stimulation-induced norepinephrine overflow and renal actions in NO-depleted conditions. We also propose that endogenous NO functions tonically as an inhibitory modulator of renal noradrenergic neurotransmission.

Involvement of nitric oxide in endothelin ETB receptor-mediated inhibitory actions on antidiuresis and norepinephrine overflow induced by stimulation of renal nerves in anesthetized dogs.

We examined the effect of sarafotoxin S6c (S6c), a selective endothelin ETB-receptor agonist, on renal actions and norepinephrine (NE) overflow induced by renal nerve stimulation (RNS) in anesthetized dogs, with or without blockade of endogenous nitric oxide (NO) generation by NG-nitro-L-arginine (NOARG), a NO synthase inhibitor. RNS (0.5-2.0 Hz) produced significant decreases in urine flow, urinary and fractional excretion of sodium, and increased NE secretion rate, without affecting systemic and renal hemodynamics. When S6c (1 ng/kg/min) was infused intrarenally, there was a slight and transient increase in renal blood flow at 1-2 min after the start of the infusion, without any change in systemic hemodynamics and this response was followed by a gradual reduction. There was a significant increase in the basal level of urine flow with no effects on urinary and fractional excretion of sodium. In addition, S6c administration elicited an increase in urinary excretion of NO metabolites. NO2- and NO3-. During S6c infusion, RNS-induced antidiuretic action and increases in NE secretion rate were significantly attenuated. RNS during intrarenal arterial infusion of NOARG (40 micrograms/kg/min) led to potent reductions in urine formation and decreased renal blood flow and glomerular filtration rate. Simultaneously. NE secretion rate was markedly increased. In the presence of NOARG, S6c-induced suppressive actions on reductions in urine formation and increase in NE secretion rate in response to RNS were markedly attenuated. The peptide did not increase urinary excretion of NO metabolites. These findings suggest that ET functions as an inhibitory modulator of renal noradrenergic neurotransmission through ETB-receptor mechanisms, events that may be caused by NO production induced by the peptide.

Effects of sarafotoxin S6c on renal haemodynamics and urine formation in anaesthetized dogs.

1. The effects of sarafotoxin S6c (S6c), a selective endothelin ETB receptor agonist, on renal haemodynamics and urine formation were examined in anaesthetized dogs. 2. Intrarenal arterial infusion of S6c at a rate of 1 or 5 ng/kg per min produced a transient increase in renal blood flow (RBF), with no change in systemic blood pressure and heart rate; RBF then decreased gradually to below the basal value. There were significant and dose-dependent increases in urine flow and free water clearance and decreases in urine osmolality during S6c infusion, whereas urinary excretion of sodium and glomerular filtration rate (GFR) remained unchanged. Simultaneously, S6c administration elicited a marked increase in urinary excretion of nitric oxide (NO) metabolites, NO2- and NO3- (UNOxV). 3. In dogs simultaneously administered S6c (5 ng/kg per min) and NG-nitro-L-arginine (NOARG; 40 micrograms/kg per min), a NO synthase inhibitor, the renal vasodilator effect of S6c was abolished and marked reductions in RBF and GFR were observed. The S6c-induced diuretic action was not affected by NOARG. In the presence of NOARG, there was a small amount of UNOxV at the basal level and the administration of S6c did not increase UNOxV. 4. These results suggest that an intrarenal arterial infusion of S6c enhances the production of NO in the kidney and that this enhancement contributes to the peptide-induced renal vasodilation. In contrast, it is unlikely that S6c-induced water diuresis is related to NO production stimulated by this peptide.

Localization and disposition of a non-peptide angiotensin II type 1 receptor antagonist, and its glucuronide metabolite, in rat.

1. The disposition of radioactivity of a non-peptide angiotensin II type 1 receptor antagonist (E4177) has been studied in groups of male rats after a single oral 1 mg/kg dose of 14C-E4177 was administered by gavage. We have also used light-microscopic autoradiography to investigate the localization of radioactivity in the target tissues for this angiotensin II receptor antagonist. 2. The radioactivity was absorbed quickly, and the maximum blood levels (Cmax) were reached at 0.38 +/- 0.14 h after dosing. The concentrations then declined bi-exponentially with a mean apparent half-life for the first phase (t1/2 alpha) of 0.46 +/- 0.07 h and a terminal half-life (t1/2 beta) of 6.22 +/- 1.08 h. By 24 h, the levels had decreased to 2.7 +/- 1.5% Cmax. The blood levels radioactivity at 48 h after administration were below the limit of quantification. 3. Radioactivity was distributed throughout the body at 15 min after administration. Tissues in which radioactivity was present at higher levels than in plasma were the liver and kidney. Radioactivity was rapidly eliminated from the tissues and was not retained in any individual organ. 4. The major route of excretion was via the bile. Since > 90% of the administered radioactivity was recovered by 24 h after administration, the excretion was relatively rapid. The major metabolite in bile was a glucuronide of E4177 biphenylcarboxylic acid (E4177-Glu). 5. Light-microscopic autoradiographic observations revealed a strong localization of radioactivity throughout the surface cells of the adrenal glomerulosa, the blood vessels in kidney and the surface of the aortic smooth muscle cells, which are all rich in angiotensin II type 1 (AT1) receptors.

Effects of sarafotoxin S6c on antidiuresis and norepinephrine overflow induced by stimulation of renal nerves in anesthetized dogs.

We previously reported that endothelin (ET) may function as an inhibitory modulator of renal noradrenergic neurotransmission (Suzuki et al., J. Cardiovasc. Pharmacol. 19: 905-910, 1992). In our study, we examined the effect of sarafotoxin S6c (S6c), a selective ET(B) receptor agonist, on changes in renal function and norepinephrine overflow induced by renal nerve stimulation (RNS) in anesthetized dogs. RNS at a low frequency (0.5-2.0 Hz) caused significant decreases in urine flow, urinary excretion of sodium and fractional excretion of sodium and increased norepinephrine secretion rate, without affecting systemic and renal hemodynamics. RNS at a high frequency (2.5-5.0 Hz), which diminishes renal hemodynamics, produced more potent decreases in urine formation and increase in norepinephrine secretion rate than seen with low frequency RNS. When S6c (1 ng/kg/min) was infused intrarenally, there was a slight and transient increase in renal blood flow, and then this response was followed by a gradual reduction. S6c administration produced increase in the basal level of urine flow with no apparent effects on urinary excretion of sodium and fractional excretion of sodium. During S6c infusion, low frequency RNS-induced antidiuretic action and increase in norepinephrine secretion rate were markedly attenuated. Qualitatively, similar results were observed in the case of high frequency RNS. In addition, high frequency RNS-induced decreases in glomerular filtration rate and filtration fraction were significantly suppressed by S6c infusion. Taken together with our previous findings, it seems likely that ET plays an important role as an inhibitory modulator of renal noradrenergic neurotransmission, through ET(B) receptor mechanisms.