Virology analyses of HCV genotype 4 isolates from patients treated with simeprevir and peginterferon/ribavirin in the Phase III RESTORE study.

Simeprevir is a hepatitis C virus NS3/4A protease inhibitor. Hepatitis C virus baseline NS3/4A polymorphisms and emerging mutations were characterized in treatment-naїve and treatment-experienced genotype 4-infected patients treated with simeprevir+peginterferon/ribavirin in the RESTORE study. Population sequencing of the NS3/4A region was performed and in vitro simeprevir activity against site-directed mutants or chimeric replicons with patient-derived NS3 protease sequences was assessed in a transient replicon assay. Simeprevir remained active against most (83/91 [91%]) baseline isolates tested in the chimeric replicon assay. Eight baseline isolates reduced simeprevir activity; these carried I132L or D168E substitutions reducing simeprevir median activity by 4.6- and 39-fold, respectively. Six of these eight isolates were from patients achieving sustained virologic response. Baseline NS3 Q80K polymorphism was not observed in the genotype 4-infected patients. Of the 107 simeprevir-treated patients, 37 did not achieve sustained virologic response for any reason. Of the 32 patients who failed treatment and had sequencing information, 28 (88%) had emerging mutations at NS3 positions 80, 122, 155, 156 and/or 168 at time of failure, similar to those in genotype 1. Emerging mutations were mainly D168V and D168E alone or combined with mutations at position 80. In general, isolates obtained at time of failure displayed high-level in vitro resistance to simeprevir (fold change ≥50) in a chimeric replicon assay with a median simeprevir fold change value of 440, consistent with observed mutations. In conclusion, emerging mutations in genotype 4 patients failing simeprevir+peginterferon/ribavirin treatment were similar to those in genotype 1 and conferred high-level resistance to simeprevir.

Identification and characterization of a new member of the genus Luteovirus from cherry.

The complete genomic sequence of a new virus from cherry trees was determined. Its genome is 5857 nt long and resembles that of members of the genus Luteovirus in its genomic organization and nucleotide sequence. Based on the species demarcation criteria for luteoviruses, the virus represents a new luteovirus species. Furthermore, a 47-nt-long inverted repeat was found at the 3' end of its genome. The virus has been provisionally named cherry-associated luteovirus (ChALV) and is the fourth member of the family Luteoviridae reported to naturally infect woody plants.

Simeprevir with peginterferon/ribavirin for treatment of chronic hepatitis C virus genotype 1 infection: pooled safety analysis from Phase IIb and III studies.

This pooled analysis of five Phase IIb and III studies evaluated the safety and tolerability of simeprevir, a once daily, oral hepatitis C virus (HCV) NS3/4A protease inhibitor. Data were summarised for patients who received simeprevir 150 mg once daily (n = 924) or placebo (n = 540) plus pegylated interferon-α/ribavirin for 12 weeks. During the first 12 weeks of treatment, few patients discontinued simeprevir or placebo due to adverse events (AEs) (both 2.2%). Pruritus (23.8% vs 17.4%), rash (any; 22.9% vs 16.7%) and photosensitivity (3.2% vs 0.6%) [Correction added on 16 January 2015, after first online publication: In the above sentence, the values in 'Photosensitivity' were previously incorrect and have now been changed to 3.2% vs 0.6%.] were more prevalent in the simeprevir vs the placebo groups. Most AEs were grade 1/2 (72.4% for simeprevir vs 71.3% for placebo). All grade 3/4 AEs occurred in <5.0% of patients, except neutropenia (9.8% vs 7.6%). Overall incidence of neutropenia was similar (17.3% vs 15.7%). Incidence of anaemia was 13.2% for simeprevir vs 10.9% for placebo, and incidence of increased bilirubin was 8.4% vs 2.8%. Bilirubin increases were mild-to-moderate and transient without concurrent transaminase increases or association with hepatic injury. Safety and tolerability did not vary with METAVIR score, although increased bilirubin and anaemia were more frequent in simeprevir-treated patients with METAVIR F4 (increased bilirubin, 13.0% vs 3.3%; anaemia, 19.0% vs 14.8%). Serious AEs were infrequent (2.1% for simeprevir vs 3.0% for placebo). No deaths were reported during the first 12 weeks of treatment. Patient-reported fatigue and other outcomes were comparable for both groups, but were of shorter duration for simeprevir due to the use of response-guided therapy. Simeprevir is well tolerated in HCV genotype 1-infected patients.

[Hippocampal stroke]. / Der hippokampale Schlaganfall.

Unilateral cerebral ischemia of the hippocampus is very rare. This paper reviews the literature and presents the case of a 59-year-old woman with an amnestic syndrome due to a left hippocampal stroke. The patient suffered from retrograde amnesia which was most severe over the 2 days prior to presenting and a slight anterograde amnesia. In addition, a verbal memory disorder was confirmed 1 week after admission by neurological tests. As risk factors, arterial hypertension and a relative hyper-beta lipoproteinemia were found. This case shows that unilateral amnestic stroke, e.g. in the hippocampus region, may be the cause of an amnestic syndrome and should be included in the differential diagnostics.

Time-of-flight angiography: a viable alternative to contrast-enhanced MR angiography and fat-suppressed T1w images for the diagnosis of cervical artery dissection?

OBJECTIVES: To compare the use of an unenhanced high-resolution time-of-flight MR angiography sequence (Hr-TOF MRA) with fat-suppressed axial/coronal T1-weighted images and contrast-enhanced angiography (standard MRI) for the diagnosis of cervical artery dissection (cDISS). METHODS: Twenty consecutive patients (9 women, 11 men, aged 24-66 years) with proven cDISS on standard MRI underwent Hr-TOF MRA at 3.0 T using dedicated surface coils. Sensitivity (SE), specificity (SP), positive and negative predictive values (PPV, NPV), Cohen's kappa (к) and accuracy of Hr-TOF MRA were calculated using the standard protocol as the gold standard. Image quality and diagnostic confidence were assessed on a four-point scale. RESULTS: Image quality was rated better for standard MRI (P = 0.02), whereas diagnostic confidence did not differ significantly (P = 0.27). There was good agreement between Hr-TOF images and the standard protocol for the presence/absence of cDISS, with к = 0.95 for reader 1 and к = 0.89 for reader 2 (P < 0.001). This resulted in SE, SP, PPV, NPV and accuracy of 97 %, 98 %, 97 %, 98 % and 97 % for reader 1 and 93 %, 96 %, 93 %, 96 % and 95 % for reader 2. CONCLUSIONS: Hr-TOF MRA can be used to diagnose cDISS with excellent agreement compared with the standard protocol. This might be useful in patients with renal insufficiency or if contrast-enhanced MR angiography is of insufficient image quality. KEY POINTS: • New magnetic resonance angiography sequences are increasingly used for vertebral artery assessment. • A high-resolution time-of-flight sequence allows the diagnosis of cervical artery dissection. • This technique allows the diagnosis without intravenous contrast medium. • It could help in renal insufficiency or when contrast-enhanced MRA fails.

Review: Lupus nephritis: pathologic features, epidemiology and a guide to therapeutic decisions.

Systemic lupus erythematosus may present with renal manifestations that frequently are difficult to categorize and lupus nephritis is an important predictor of poor outcome. The type and spectrum of renal injury may remain undiagnosed until full-blown nephritic and/or nephrotic syndrome appear with increased risk of end-stage renal disease. These abnormalities occur within the first few years after the diagnosis of lupus is made on clinical grounds and with the support of laboratory tests in high risk patients. An early renal biopsy is helpful in patients with an abnormal urinalysis and/or reduced glomerular filtration rate and the results form the basis for therapeutic decisions. The biopsy also provides vital prognostic information based on histological categorization of different types of lupus nephritis, the degree of activity, chronicity and the immunopathogenesis. In the current armamentarium, the use of cyclophosphamide and azathioprine and recently mycophenolate mofetil, reduce morbidity and maintenance therapies reduce the risk of end-stage renal disease. Clinical trials underway promise new, effective and safe immunosuppressive regimens for the treatment of proliferative lupus nephritis.

Bringing biocatalytic deuteration into the toolbox of asymmetric isotopic labelling techniques.

Enzymes dependent on nicotinamide cofactors are important components of the expanding range of asymmetric synthetic techniques. New challenges in asymmetric catalysis are arising in the field of deuterium labelling, where compounds bearing deuterium (2H) atoms at chiral centres are becoming increasingly desirable targets for pharmaceutical and analytical chemists. However, utilisation of NADH-dependent enzymes for 2H-labelling is not straightforward, owing to difficulties in supplying a suitably isotopically-labelled cofactor ([4-2H]-NADH). Here we report on a strategy that combines a clean reductant (H2) with a cheap source of 2H-atoms (2H2O) to generate and recycle [4-2H]-NADH. By coupling [4-2H]-NADH-recycling to an array of C=O, C=N, and C=C bond reductases, we demonstrate asymmetric deuteration across a range of organic molecules under ambient conditions with near-perfect chemo-, stereo- and isotopic selectivity. We demonstrate the synthetic utility of the system by applying it in the isolation of the heavy drug (1S,3'R)-[2',2',3'-2H3]-solifenacin fumarate on a preparative scale.

[Nephrogenic fibrosing dermopathy or nephrogenic systemic fibrosis? What do we know and what do we have to learn?]. / Dermopatía fibrosante nefrogénica o fibrosis sistémica nefrogénica? Qué es lo que sabemos y qué debemos aprender?

Nephrogenic systemic fibrosis (NSF) was first recognized as a unique entity in 1997 and subsequently defined in the literature in 2000 as a novel fibrosing disorder occurring in the setting of renal disease. Prevention, early recognition and treatment are essential to limiting its impact. The most important risk factors for developing NSF are chronic or significant acute kidney disease (especially dialysis dependent patients) and the administration of gadolinium (GD3) containing contrast agents, agents that cause NSF by releasing free gadolinium (GD3) into tissues based on their pharmacokinetics. International commissions in drug control and medicinal products recommend to avoid gadolinium based contrast agents in patients with GFR < 30 ml/minute/1.73 m(2). Unfortunately there is lack of universally effective therapy at this time and the literature is based on case reports and small case series. Recommendations to guide the use of gadolinium based contrast agents in patients with underlying kidney disease should be individualized and considered in consultation with the ordering physician, radiologist and nephrologist.

Discriminating changes in intracellular NADH/NAD+ levels due to anoxicity and H2 supply in R. eutropha cells using the Frex fluorescence sensor.

The hydrogen-oxidizing "Knallgas" bacterium Ralstonia eutropha can thrive in aerobic and anaerobic environments and readily switches between heterotrophic and autotrophic metabolism, making it an attractive host for biotechnological applications including the sustainable H2-driven production of hydrocarbons. The soluble hydrogenase (SH), one out of four different [NiFe]-hydrogenases in R. eutropha, mediates H2 oxidation even in the presence of O2, thus providing an ideal model system for biological hydrogen production and utilization. The SH reversibly couples H2 oxidation with the reduction of NAD+ to NADH, thereby enabling the sustainable regeneration of this biotechnologically important nicotinamide cofactor. Thus, understanding the interaction of the SH with the cellular NADH/NAD+ pool is of high interest. Here, we applied the fluorescent biosensor Frex to measure changes in cytoplasmic [NADH] in R. eutropha cells under different gas supply conditions. The results show that Frex is well-suited to distinguish SH-mediated changes in the cytoplasmic redox status from effects of general anaerobiosis of the respiratory chain. Upon H2 supply, the Frex reporter reveals a robust fluorescence response and allows for monitoring rapid changes in cellular [NADH]. Compared to the Peredox fluorescence reporter, Frex displays a diminished NADH affinity, which prevents the saturation of the sensor under typical bacterial [NADH] levels. Thus, Frex is a valuable reporter for on-line monitoring of the [NADH]/[NAD+] redox state in living cells of R. eutropha and other proteobacteria. Based on these results, strategies for a rational optimization of fluorescent NADH sensors are discussed.

Failure to phosphorylate AKT in podocytes from mice with early diabetic nephropathy promotes cell death.

Loss of podocytes by apoptosis characterizes the early stages of diabetic nephropathy. To examine its mechanism we studied glomeruli and podocytes isolated from db/db mice with early diabetic nephropathy and albuminuria. Phosphorylation of AKT (protein kinase B, a key survival protein) was found to be lower in the glomeruli of 12 week old db/db compared to db/+ mice. In vitro, insulin phosphorylated AKT solely in podocytes from db/+ mice. Serum deprivation and exposure to tumor necrosis factor-alpha significantly compromised cell viability in podocytes from db/db but not from db/+ mice, and this was associated with a significant decrease in AKT phosphorylation. Inhibition of AKT was necessary to achieve the same degree of cell death in db/+ podocytes. Our study shows that podocyte inability to respond to insulin and susceptibility to cell death may partially account for the decreased podocyte number seen in early diabetic nephropathy.

Investigating the sensitivity of a fluorescence-based microarray for the detection of fruit-tree viruses.

An oligonucleotide microarray for the detection of some fruit-tree viruses was designed and its theoretical detection limit was assessed using Cy3-labelled oligonucleotides. The real sensitivity of the microarray was compared for different kinds of fluorescently labelled targets: (a) cDNA and PCR amplified targets, (b) PCR amplified targets labelled using three different labelling methods. In the first case (a), the number of viral cDNA molecules was below the assessed detection limit of the microarray and only PCR amplified targets were detected. A second comparison (b), done on 3 selected viruses, included indirect labelling, the direct incorporation of labelled-dUTPs, and the use of Cy3-labelled primer. The targets labelled most intensively were produced by the Cy3-primer labelling (2 of 3 viruses) or by the indirect labelling method (1 of 3 viruses), the weakest signal showed targets labelled directly (all 3 viruses). The use of Cy3-primer labelling involved the simplest preparation and the lowest cost, however occasional weak cross-hybridization appeared. The indirect labelling method was of the highest specificity. The probes hybridizing near the 3-end of the targets showed the lowest intensities of fluorescent signal.

P3M algorithm for dipolar interactions.

An extension to the P(3)M algorithm for electrostatic interactions is presented that allows to efficiently compute dipolar interactions in periodic boundary conditions. Theoretical estimates for the root-mean-square error of the forces, torques, and the energy are derived. The applicability of the estimates is tested and confirmed in several numerical examples. A comparison of the computational performance of the new algorithm to a standard dipolar-Ewald summation methods shows a performance crossover from the Ewald method to the dipolar P(3)M method for as few as 300 dipolar particles. In larger systems, the new algorithm represents a substantial improvement in performance with respect to the dipolar standard Ewald method. Finally, a test comparing point-dipole-based and charged-pair based models shows that point-dipole-based models exhibit a better performance than charged-pair based models.

New directions in the management of severe lupus nephritis.

Systemic lupus erythematosus, which predominantly affects young women, frequently is complicated by renal involvement. The presence of acute glomerulonephritis significantly adds to morbidity and mortality. Based on currently published clinical trials, induction therapy with cyclophosphamide combined with pulse corticosteroids is an efficacious treatment option to preserve renal function, and long-term data are available to support this choice. Mycophenolate mofetil is a promising new agent, and recent data suggest that it is at least as efficacious as cyclophosphamide in the induction and maintenance phase, but with fewer side effects. Cell-depleting agents may be added in patients who fail the traditional regimens, preferentially in the setting of one of the ongoing clinical trials. The number of treatment regimens that the clinician can choose from when confronted with a patient with severe lupus nephritis has increased significantly, and more options are on the horizon. This promises more efficacious and better tolerable therapies, but it also puts an additional obligation on the physician to consider risk-to-benefit ratio, patient preference and adherence, feasibility, and cost; and to engage the patient in an active discussion about the different alternatives.

IGF-1 decreases collagen degradation in diabetic NOD mesangial cells: implications for diabetic nephropathy.

Nonobese diabetic (NOD) mice develop glomerulosclerosis shortly after the onset of diabetes. We showed that mesangial cells (MCs) from diabetic mice exhibited a stable phenotypic switch, consisting of both increased IGF-1 synthesis and proliferation (Elliot SJ, Striker LJ, Hattori M, Yang CW, He CJ, Peten EP, Striker GE: Mesangial cells from diabetic NOD mice constitutively secrete increased amounts of insulin-like growth factor-I. Endocrinology 133:1783-1788, 1993). Because the extracellular matrix (ECM) accumulation in diabetic glomerulosclerosis may be partly due to decreased degradation, we examined the effect of excess IGF-1 on collagen turnover and the activity of metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) in diabetic and nondiabetic NOD-MC. Total collagen degradation was reduced by 58 +/- 18% in diabetic NOD-MCs, which correlated with a constitutive decrease in MMP-2 activity and mRNA levels, and nearly undetectable MMP-9 activity and mRNA. TIMP levels were slightly decreased in diabetic NOD-MC. The addition of recombinant IGF-1 to nondiabetic NOD-MC resulted in a decrease in MMP-2 and TIMP activity. Furthermore, treatment of diabetic NOD-MC with a neutralizing antibody against IGF-1 increased the latent form, and restored the active form, of MMP-2. In conclusion, the excessive production of IGF-1 contributes to the altered ECM turnover in diabetic NOD-MC, largely through a reduction of MMP-2 activity. These data suggest that IGF-1 could be a major contributor to the development of diabetic glomerulosclerosis.

Oligonucleotide-based microarray: a new improvement in microarray detection of plant viruses.

Microarrays are one of the new emerging methods in plant virology currently being developed by various laboratories. In this study, a new approach is described on the detection of plant viruses using short synthetic single-stranded oligomers (40 nt) instead of PCR products as capture probes. A microchip detecting potato viruses, PVA, PVS, PVM, PVX, PVY and PLRV, in both single and mixed infections was developed and tested. The chip was also designed to distinguish between the main strains of PVY and PVS. Results of initial tests with PVY(NTN) and PVY(O) strains using several different probes for one virus are presented. Possibilities and advantages of the new oligonucleotide-based microarray approach for plant viral diagnosis are discussed.

Characterization of the active site of a hydrogen sensor from Alcaligenes eutrophus.

A third hydrogenase was recently identified in the proteobacterium Alcaligenes eutrophus as a constituent of a novel H2-sensing multicomponent regulatory system. This regulatory hydrogenase (RH) has been overexpressed in cells deficient in both the NAD+-reducing [NiFe]-hydrogenase and the membrane-bound [NiFe]-hydrogenase. EPR, FTIR and activity studies of membrane-free extracts revealed that the RH has an active site much like that of standard [NiFe]-hydrogenases, i.e. a Ni-Fe site with two CN- groups and one CO molecule. Its catalytic power is low, but the RH is always active, insensitive to oxygen, and occurs in only two redox states.

Matrix accumulation in mesangial cells exposed to cyclosporine A requires a permissive genetic background.

BACKGROUND: Chronic nephrotoxicity is an important adverse effect of cyclosporine A (CsA) therapy. Tubulo-interstitial lesions and arteriolopathy are common histologic findings. Glomerular lesions are also described, but they are of variable severity. The aim of our study is to determine whether CsA has a direct effect on mesangial cells and whether the cellular response depends on the genetic background. METHODS: We studied mesangial cells isolated from mice susceptible (ROP/Le-+Es1(b)+Es1(a), ROP) and resistant to glomerulosclerosis (B6SJLF1, C57). We previously showed that sclerosis-prone and sclerosis-resistant phenotypes are maintained in vitro. We examined whether CsA exposure directly affected extracellular matrix turnover in mesangial cells and whether the response is determined by the genetic background. Extracellular matrix synthesis and degradation were studied by proline incorporation, ELISA, reverse transcription-polymerase chain reaction, zymography, and reverse zymography. We chose a CsA dose that induced neither cytotoxicity nor apoptosis (1 microg/ml). RESULTS: At the dose of 1 microg/ml total collagen accumulation was increased in ROP but not in C57 cells. Matrix metalloproteinase (MMP)-2 activity and mRNA levels were selectively decreased in ROP cells. CsA exposure did not affect tissue inhibitors of MMP (TIMP)-1 and -2 activity or TGF-beta1 mRNA expression and protein synthesis in either cell line. CONCLUSION: CsA increases total collagen accumulation in mesangial cells from sclerosis-prone mice by decreasing MMP-2 activity, but does not affect cells from sclerosis-resistant mice. Thus, CsA directly affects mesangial cells, but only those with a permissive genetic background for glomerulosclerosis.

Investigation of the negative inotropic effects of 17 beta-oestradiol in human isolated myocardial tissues.

1. The aim of the present study was to evaluate the effects of 17 beta-oestradiol in human myocardium. The effects of 17 beta-oestradiol, progesterone and testosterone on force of contraction were investigated in electrically driven isolated atrial trabeculae and ventricular papillary muscles from human hearts in the presence and absence of Bay K 8644, a calcium channel agonist. In addition, the effects of 17 beta-oestradiol, progesterone and testosterone on binding of [3H]-PN 200 110 were assessed in membranes prepared from human ventricular myocardium. 2. 17 beta-Oestradiol elicited a negative inotropic effect in atrial (IC50: 7.1 mumol 1(-1), confidence interval 3.8 to 13.4, n = 3) and ventricular preparations (IC50: 4.6 mumol 1(-1)), confidence interval 2.2 to 9.4, n = 3) as compared with solvent controls. There was no significant difference (P > 0.05) of IC50 values in the absence and presence of isoprenaline (0.0 mumol 1(-1)) in atrial (IC50: 10.8 mumol 1(-1), confidence interval 9.1 to 12.9, n = 6) and ventricular preparations (IC50: 9.4 mumol 1(-1), confidence interval 7.3 to 11.9, n = 8). 3. 17 beta-Oestradiol at 30 mumol 1(-1) induced a significant rightward shift of the concentration-response curves for the positive inotropic effect of Bay K 8644 in atrial preparations (EC50: 0.13 mumol 1(-1), confidence interval 0.08 to 0.19, n = 6; EC50 with 17 beta-oestradiol: 0.58 mumol 1(-1), confidence interval 0.33 to 0.83, n = 6, P < 0.05) and ventricular preparations (EC50: 0.07 mumol 1(-1), confidence interval 0.04 to 0.11, n = 8; EC50 with 17 beta-oestradiol: 0.3 mumol 1(-1), confidence interval 0.18 to 0.49, n = 8, P < 0.05). Testosterone, progesterone at 30 mumol 1(-1) and the solvent control had no significant effect on the concentration-response curves to Bay K 8644. 4. In membranes prepared from human ventricular myocardium the effect of 17 beta-oestradiol on binding of [3H]-PN 200 110, an antagonist at the 1,4 dihydropyridine binding site, was not different from that observed with progesterone, testosterone or solvent controls. 5. In myocardial membranes no specific oestrogen receptors were demonstrated by [3H]-oestradiol binding studies. 6. Thus, the calcium antagonistic property of 17 beta-oestradiol cannot be attributed to a direct interaction with 1, 4 dihydropyridine binding sites.

Cardiac angiotensin II receptors: studies on functional coupling in Sprague-Dawley rats and TGR(alphaMHC-hAT1) transgenic rats.

The renin-angiotensin system plays an important role in the pathogenesis of cardiac hypertrophy and chronic heart failure as angiotensin II has been shown to induce cardiac hypertrophy and fibrosis. Besides these structural alterations, functional effects on cardiomyocytes have been reported in different mammalian species. Angiotensin II is known to produce a positive inotropic effect in some species, and differences in atrial and ventricular myocardium have been described. So far, the molecular events which govern angiotensin II-mediated changes in cardiac contractility are not completely understood. In order to study the dependency of the angiotensin II-induced positive inotropic effect on receptor density, we examined the effect of angiotensin II on cardiac function in atria, papillary muscles and isolated ventricular cardiomyocytes from adult Sprague-Dawley rats and TGR(alphaMHC-hAT1) transgenic rats, which expressed the human angiotensin AT1 receptor (hAT1) specifically in the heart. In atrial myocardium from adult Sprague-Dawley rats, angiotensin II (30 micromol/l) produced an AT1-mediated positive inotropic effect (38.5% of control), whereas in papillary muscles and isolated ventricular myocytes, no inotropic response was observed. As shown by polymerase chain reaction (PCR) and radioligand binding, the human angiotensin AT1 receptor was exclusively expressed in transgenic animals, which markedly overexpressed the angiotensin AT1 receptor. However, in transgenic rats the positive inotropic effect in atrial preparations was similar to the controls, and neither in papillary muscles nor in isolated cardiomyocytes the increase in receptor density led to an inotropic effect induced by angiotensin II. These data suggest that the existence of functionally uncoupled receptors rather than the low density of receptors at the ventricular site is responsible for the inability of ventricular myocardium to respond to angiotensin II.

Effects of angiotensin II and angiotensin-converting enzyme inhibitors on human myocardium.

Human myocardial angiotensin II receptors and the angiotensin AT1 and AT2 receptor subtypes were characterised using the partial angiotensin II receptor agonist [125I][Sar1,IIe8]angiotensin II and the selective antagonists losartan (2-n-butyl-4-chloro-5-hydroxymethyl-1-[2'((1H-tetrazol-5-yl)biphen yl-4-yl)- methyl]imidazole) and PD 123177 (1-[(4-amino-3-methylphenyl)methyl]-5-(diphenyl-acetyl)- 4,5,6,7-tetrahydro-1H-imidazol[4,5-c]pyridine-6-carboxylic acid). The density of angiotensin II receptors was higher in atrial than in ventricular myocardium. Angiotensin AT2 receptors were predominant in atria and ventricles (80-85% of total angiotensin II receptors). Only in isolated, electrically driven atrial trabeculae but not in ventricular preparations, angiotensin II did produce a concentration-dependent positive inotropic effect, which was antagonized exclusively by the angiotensin AT1 receptor antagonist losartan and which amounted to about 20% of the positive inotropic effect of milrinone and isoprenaline. The application of the angiotensin-converting enzyme inhibitors captopril, enalaprilat and ramiprilat had no inotropic effect in either tissue. It is concluded that angiotensin AT1 receptors exclusively mediate direct positive inotropic effects in atrial myocardium. Since angiotensin-converting enzyme inhibitors do not produce any inotropic effect, tonic regulation of basal force of contraction by angiotensin II does not occur.