Biomedical subjects

S Harder

Publications and source records attributed to S Harder.

At least 37 records · Page 2Linked to original sources

PubMed2001

T-large granular lymphocyte leukaemia with natural killer cell-like cytotoxicity and expression of two different alpha- and beta-T-cell receptor chains.

We describe a case of cytotoxic T-large granular lymphocyte leukaemia showing typical morphological features, expressing antigens characteristic for cytotoxic T cells and exhibiting marked natural killer-like cytotoxicity towards different target cells. Moreover, characterization of the T-cell receptors revealed simultaneous expression of two different types of beta-chains as well as alpha-chains by the malignant cell clone. The patient had an 8 year history of indolent disease, before progressing to an aggressive clinical course hardly responsive to chemotherapeutic treatment. This is the first description of a peripheral T-cell neoplasm expressing four distinct types of T-cell receptor molecules.

Disease Progression↗

PubMed2001

Angiotensin II infusion increases plasma erythropoietin levels via an angiotensin II type 1 receptor-dependent pathway.

BACKGROUND: Angiotensin-converting enzyme inhibitors (ACEIs) have been shown to lower hematocrit and erythropoietin (EPO), but a direct link between angiotensin II (Ang II) and EPO in humans has not been shown. METHODS: Placebo or Ang II was infused for six hours in nine healthy male volunteers with and without blockade of the Ang II subtype 1 receptor (AT1R). EPO concentrations were measured 3, 6, 12, and 24 hours after the start of the infusion. RESULTS: Ang II raised the mean arterial pressure by about 20 mm Hg. Consistent with the known diurnal variation, EPO levels rose significantly (P < or = 0.02) during the day in all groups. During Ang II infusion, EPO levels rose to significantly higher levels after 6 and 12 hours compared with placebo [9.9 +/- 3.5 vs. 7.2 +/- 3.1 mU/mL (3 h, P = NS); 16.9 +/- 4.5 vs. 8.8 +/- 3.7 mU/mL (6 h, P = 0.01); 17.0 +/- 8.6 vs. 11.1 +/- 4.7 mU/mL (12 h, P = 0.01)] and returned to baseline after 24 hours (7.9 +/- 3.8 vs. 10.6 +/- 8.6 mU/mL, P = NS). With AT1R blockade, blood pressure remained normal during Ang II infusion, and EPO levels were never significantly different from placebo [6.8 +/- 4.8, 10.5 +/- 5.6, 13.1 +/- 9.0, and 12.4 +/- 10.1 mU/mL at 3, 6, 12, and 24 h after infusion, respectively, P = NS]. CONCLUSIONS: Ang II increases EPO levels in humans. This increase requires the participation of AT1R.

Adult↗

PubMed2001

Levodopa pharmacokinetic-pharmacodynamic modeling and 6-[18F]levodopa positron emission tomography in patients with Parkinson's disease.

OBJECTIVE: Parameters of a pharmacokinetic-pharmacodynamic (PK-PD) model of levodopa have been claimed to reflect the magnitude of the dopaminergic deficit in patients with Parkinson's disease. The aim of this study was to correlate such parameters with positron emission tomography (PET) with levodopa tagged with 6-fluorine 18, an established imaging method for striatal dopaminergic neurons. METHODS: Twenty-three patients in different disease stages (Hoehm and Yahr stage 2.5-5 [Hoehn MM, Yahr MD. Parkinsonism: onset, progression and mortality. Neurology 1967;4:427-42]; median duration, 12 years) were studied. PK-PD modeling followed a single oral dose of levodopa/benserazide. The sum score of the Columbia Rating Scale (CURSSigma) was used for clinical assessments. A nonparametric effect compartment approach assuming a sigmoidal E(max) model was applied to the PK-PD analysis of plasma levodopa concentrations and corresponding CURSSigma. Thereafter 6-[18F]levodopa PET was performed, and the influx rate constants (k(c)) for the putamen and the caudatus region were correlated with the median effective concentration (EC(50)) and the equilibrium half-life (T(eq)) of the PK-PD model. RESULTS: (1) A significant correlation was observed between PK-PD parameters or with k(c) putamen as the dependent variable and the duration of the disease as the independent variable, which explains 33% of the variability of the EC(50), 42% of the variability of T(eq), and 36% of the variability of k(c). (2) Significant correlations were observed between k(c) and either EC(50) or T(eq), yielding the closest correlation for the putamen region (r = -0.47, P <.05; and r = 0.55, P <.01; respectively). CONCLUSIONS: Our findings show that key parameters of a PK-PD model of levodopa were in fairly close agreement with imaging of dopaminergic neurons by 6-[18F]levodopa PET. However, although PK-PD modeling of levodopa has been proven as a useful investigation of approaches aimed to restore dopaminergic deficits or to monitor disease progression, this modeling cannot serve as a pathomorphologic surrogate for the loss of striatal dopaminergic neurons.

Adult↗

PubMed2001

Regulator of G protein signaling 4 suppresses basal and thyrotropin releasing-hormone (TRH)-stimulated signaling by two mouse TRH receptors, TRH-R(1) and TRH-R(2).

We cloned the mouse TRH receptor type 2 (mTRH-R2) gene, which is 92% identical with rat TRH-R2 and 50% identical with mTRH-R1 at the amino acid level, and identified an intron within the coding sequence that is not present in the TRH-R1 gene structure. Similar to its rat homolog, mTRH-R2 binds TRH with an affinity indistinguishable from mTRH-R1, signals via the phosphoinositide pathway like mTRH-R1, but exhibits a higher basal signaling activity than mTRH-R1. We found that regulator of G protein signaling 4 (RGS4), which differentially inhibits signaling by other receptors that couple to Gq, inhibits TRH-stimulated signaling via mTRH-R1 and mTRH-R2 to similar extents. In contrast, other RGS proteins including RGS7, RGS9, and GAIP had no effect on signaling by mTRH-R1 or mTRH-R2 demonstrating the specificity of RGS4 action. Interestingly, RGS4 markedly inhibited basal signaling by mTRH-R2. Inhibition of basal signaling of mTRH-R2 by RGS4 suggests that modulation of agonist-independent signaling may be an important mechanism of regulation of G protein-coupled receptor activity under normal physiologic circumstances.

Amino Acid Sequence↗

PubMed2001

Pharmacokinetic-pharmacodynamic relationship of levodopa with and without tolcapone in patients with Parkinson's disease.

OBJECTIVE: To investigate the effect of administration of the catechol-Omethyltransferase (COMT) inhibitor tolcapone on the concentration-effect relationship of levodopa in patients with advanced Parkinson's disease and on-off fluctuations. DESIGN: Nonblind single-group 2-period pharmacokinetic-pharmacodynamic study. PATIENTS AND PARTICIPANTS: 12 patients, mean age 59 years, with idiopathic Parkinson's disease and response fluctuations. METHODS: The pharmacokinetics [plasma concentrations of levodopa and 3-O-methyldopa (3-OMD)] and motor effects [global score of the Columbia University Rating Scale (CURSsigma)] of levodopa (plus the peripheral decarboxylase inhibitor benserazide 1:4) were determined for 4 consecutive dosage intervals (4 hours each, starting at 8.00am) in 12 patients before (day 1) and during (day 8) coadministration of tolcapone 100 mg 3 times daily for 7 days. RESULTS: Under tolcapone, exposure to levodopa [area under the plasma concentration-time for the dosage interval (AUCt)] observed for the separate doses increased by 1.6- to 2.2-fold, and peak plasma drug concentrations (Cmax) increased by 1.1 - to 2.1 -fold. 3-OMD concentrations at day 8 were reduced to about 20% of the values at day 1. At baseline (day 1, before the first levodopa dose), CURSsigma averaged 40 +/- 10 points. After the first levodopa dose. CURSsigma declined to 20 +/- 9 points. At day 8. the predose CURSsigma decreased to a final score of 31 +/-13 points, and the maximal decline after the first levodopa dose was to a final score of 16 +/- 8 points. Population analysis (NONMEM) of the concentration-effect relationship of levodopa according to a sigmoidal Emax model and over all dosage intervals did not show differences in levodopa responsiveness with or without tolcapone. The population mean of the 50% effective concentration (EC50) of levodopa was 1350 microg/L with an standard error of the population parameter estimate of 18%: adding tolcapone treatment as a covariate did not significantly change the population fit. Circadian influences on levodopa respon- siveness were not evaluable by the NONMEM model due to overparametrisation, but visual inspection of plotted data did not suggest differences in the concentration-effect relationship between the 4 consecutive dosage intervals on days 1 and 8. CONCLUSIONS: The gain in clinical improvement with levodopa under tolcapone can be fully explained by tolcapone-induced changes of peripheral levodopa pharmacokinetics. We suggest that this interaction study, performed in patients and using clinical data, excludes any central effects of tolcapone or any inhibiting effect of 3-OMD on levodopa permeation through the blood-brain barrier, which otherwise would have led to a decrease in the EC50 of levodopa.

Aged↗

PubMed2001

Lipid-lowering treatment in coronary artery disease: a survey in an ambulatory outpatient clinic.

OBJECTIVES: In controlled trials, HMG-CoA reductase inhibitors (statins) effectively reduced cardiovascular events in patients with coronary artery disease (CAD). However, recent pharmacoepidemiological studies indicate an underuse of statins in the target population. The objective of this study was to examine the extent to which CAD patients in Germany actually received statins under field conditions. METHODS: We evaluated the medical records of 296 patients referred to the cardiology outpatient clinic of the Frankfurt University Hospital by their general practitioner (GP) in the period 1995 to 1998. All patients had symptomatic, angiographically proven CAD, 142 had previous myocardial infarction. A diagnosis of dyslipidemia was taken from the records. Most patients were visited on more than 1 occasion. In all, we were able to access 296 records for a 1st visit, 76 records for a 2nd visit and 29 records for a 3rd visit and 16 records for > 3 visits. RESULTS: According to the entry criteria of the 4S Trial (total cholesterol 5.5-8.0 mmol/l or 212-311 mg/dl), 108 patients were deemed as eligible for lipid-lowering treatment, criteria of the LIPID Trial (4.0-7.0 mmol/l or 154-270 mg/dl) gave a yield of 190 patients. The actual treatment rate with a statin at the 1st visit was 34% (LIPID Group) and 40% (4S Group). At later visits, the treatment rates with statins increased to 63% (LIPID Group) and 79% (4S Group), due to advice given to the GP by the outpatient clinic. When the observation period was devided into 2 periods (04/95 - 01/97; 02/97 - 09/98), actual treatment rates (all visits) for the 4S Group were 43% and 38%, respectively, indicating no further "penetration" of the 4S Study in the therapy decision-making of the GPs. CONCLUSIONS: The data indicate that necessary treatment with a HMG-CoA reductase inhibitor is often withheld in the ambulatory setting.

Adult↗

PubMed2000

Mycophenolate mofetil decreases endothelial prostaglandin E2 in response to allogeneic T cells or cytokines.

BACKGROUND: Prostaglandin E2 (PGE2) is a powerful endogenous immune suppressant and interferes with various T-cell functions. However, it is not known in detail whether immunosuppressive drugs influence the PGE2-driven immune response in transplant patients. Therefore, we investigated the effect of several immunosuppressive compounds, in particular the novel drug mycophenolate mofetil (MMF), on endothelial PGE2 release. METHODS: Endothelial cells (HUVEC) were activated by either allogeneic CD4+ or CD8+ T cells, or by the cytokines interleukin-1 or gamma-interferon. Using an enzyme-linked immunosorbent assay, we analyzed PGE2 release of the activated HWEC in the presence of MMF, cyclosporine, or tacrolimus. As verapamil and mibefradil also possess immunosuppressive properties, they were included in the study as well. RESULTS: Activation of HUVEC with interleukin-1 or T cells resulted in a drastic accumulation of PGE2 in the supernatant. Cyclosporine or tacrolimus had no effect on PGE2 release. However, Ca2+ channel blockers, when applied at higher dosages, caused a significant increase in PGE2. Interestingly, MMF strongly diminished the PGE2 level in the cell culture supernatant in a concentration-dependent manner. CONCLUSION: The results demonstrate an inhibitory effect of MMF on PGE2 production, which may lower the benefits of the PGE2-triggered immune response after organ transplantation.

Cells, Cultured↗

PubMed2000

In vitro analysis of verapamil-induced immunosuppression: potent inhibition of T cell motility and lymphocytic transmigration through allogeneic endothelial cells.

BACKGROUND: Cyclosporine A (CsA) and tacrolimus prevent proliferation but not transendothelial migration of alloreactive lymphocytes into donor organs. As a result, serious adverse effects, such as nephrotoxicity and neurotoxicity, have been observed under CsA/tacrolimus therapy. The incorporation of new drugs with infiltration blocking properties might enhance the efficacy of the current immunosuppressive protocol, allowing lower CsA/tacrolimus dosage. Because Ca2+ plays a critical role in cell-cell interaction, the Ca2+-channel blocker verapamil might be a good cany. didate for supporting CsA/tacrolimus-based therapy. METHODS: A T-cell endothelial cell coculture model or immobilized immunoglobulin G globulin chimeras were employed to investigate how S- and R- verapamil interfere with the lymphocytic infiltration process. The expression and arrangement of membranous adhesion receptors and cytoskeletal F-actin filaments were analyzed by fluorometric method in the presence of. verapamil. RESULTS: Both verapamil enantiomers strongly inhibited lymphocyte infiltration. CD4+ and CD8+ T-cells were influenced to a similar extent with regard to horizontal locomotion (CD4+=CD8+), but to a different extent with regard to adhesion and penetration (CD4+ > CD8+). Moreover, penetration was blocked to a higher extent than was adhesion. ID50-values were 31 microM (CD4+-adhesion) and 11 microM (CD4+-penetration). Verapamil reduced P-selectin expression on endothelial cells and effectively down-regulated binding of T-cells to immobilized P-selectin immunoglobulin G globulins (ID50=4.4 microM; CD4+). A verapamil-induced reduction of intracellular F-actin in T-lymphocytes was proven to be mainly responsible for diminished cell locomotion. CONCLUSIONS: The prevention of CD4+ T-cell penetration by verapamil might argue for its use as an adjunct to CsA/tacrolimus-based immunosuppressive therapy.

Cell Movement↗

PubMed2000

Differential in vitro effects of the platelet glycoprotein IIb/IIIa inhibitors abixicimab or SR121566A on platelet aggregation, fibrinogen binding and platelet secretory parameters.

The aim of this study was to compare fibrinogen binding, inhibition of platelet aggregation and secretory potential of the MAb abciximab (0.5-5 microg/mL) and the peptidomimetic compound SR121566A (15-250 ng/mL) in vitro in whole blood. Fibrinogen binding was followed by flow cytometry; platelet function was evaluated by light transmittance and by impedance aggregometry. Secretory functions of platelets were evaluated using ATP as marker for early secretion by dense granulae and P-selectin (CD62) for alpha-granular secretion as well as CD63 for lysosomal degranulation. Results showed that fibrinogen binding induced by 5 microM TRAP was maximally inhibited greater than 80% at 3 microg/mL abciximab or at 250 ng/mL SR121566A. At these concentrations of antagonists, platelet aggregation induced by 5 microM ADP or 2 microg/mL collagen was inhibited completely. Expression of CD62 was reduced 34% with abciximab or 15% with SR121566A; CD63 expression was reduced 22% with both agents. With both agents, the EC50 for inhibition of CD62 and CD63 expressions was in similar magnitudes than the EC50 for fibrinogen binding inhibition. With 3 microg/mL abciximab, ATP secretion was maximally reduced to 50% of the control, whereas SR121566A at 250 ng/mL had no inhibitory effect on this parameter. A slight increase in ATP secretion was seen with 0.5 microg/mL abciximab and with SR121566A in concentrations of less than 45 ng/mL. The data suggest a discoupling between the anti-aggregatory and the antisecretory effects of IIb/IIIa antagonists. Because it is not established to what extend CD62 or CD63 expression can be reduced by any means, the reduction by 20-30% obtained by 3 microg/mL abciximab or 250 ng/mL SR121566A might already be the maximum possible inhibition by these agents.

Adenosine Triphosphate↗

PubMed2000

A 3-cM commonly deleted region in 6q21 in leukemias and lymphomas delineated by fluorescence in situ hybridization.

Deletions of the long arm of chromosome 6 (6q) are frequent chromosome aberrations in non-Hodgkin lymphomas (NHLs) and acute lymphoblastic leukemias (ALLs). It is presumed that one or more tumor suppressor genes are localized on 6q. By means of fluorescence in situ hybridization (FISH), we attempted to detect and delineate deletions of 6q in leukemias and lymphomas. We performed FISH on 148 cases of lymphoma and acute leukemia using a panel of 36 YAC probes distributed from 6q12 to 6q27 and a centromeric probe of chromosome 6 as internal control. Deletions of 6q that included a 7-cM commonly deleted region in 6q21 were detected in 59 patients who had B- and T-cell low-grade and high-grade NHL and ALL. FISH with two YAC probes flanking this region was performed on an additional 97 cases of NHL and leukemia. Deletions in 6q21 were detected in an additional 21 cases. In five cases of high-grade B- and T-cell NHL and ALL, the deletion breakpoints were located within the commonly deleted region. To define the deletion breakpoints exactly and to narrow this region further, FISH was performed with six additional YAC probes that have been physically localized within this region. A 3-cM (4-5 Mb) commonly deleted region in 6q21 was delineated. Our study suggests that this commonly deleted region harbors a putative tumor suppressor gene involved in the pathogenesis of both low-grade and high-grade NHL and ALL. Genes Chromosomes Cancer 27:52-58, 2000.

Chromosome Deletion↗

PubMed2000

The effect of exercise on pharmacokinetics and pharmacodynamics of levodopa.

The aim of our study was to evaluate the influence of low-intensity exercise on levodopa absorption and levodopa motor effect. We studied the pharmacokinetics and pharmacodynamics of levodopa under resting conditions and under a workload of 50 watts for 2 hours on a cycle ergometer in 12 parkinsonian patients with predictable fluctuations of motor disability. The patients attended the hospital on both days in a provoked off state. After a baseline assessment of motor disability using the Columbia University rating scale (CURS scale) and a blood test for measurement of the baseline levodopa concentration in the plasma, 100 mg levodopa and 25 mg benserazide were administered as a single dose orally. Blood samples for measurement of the levodopa concentration in the plasma were taken, and motor assessments were conducted at 15-minute intervals for 240 minutes and at 30-minute intervals from 240 to 360 minutes. All patients were able to perform the exercise program. The baseline Columbia University rating scale score did not differ significantly between both days. The mean levodopa concentration in plasma at half-maximal motor effect tended to be higher during exercise and indicated that the patients needed a higher levodopa concentration in plasma to achieve the half-maximal motor effect. The maximal levodopa concentration in plasma tended to be higher with exercise. Both trends did not reach statistical significance. In summary, there was not a negative or a positive net effect of exercise on pharmacokinetics and pharmacodynamics of levodopa. However, there were two counteracting trends: a trend toward better levodopa absorption and a trend toward a deteriorated concentration-effect correlation.

Administration, Oral↗

PubMed2000

Feasibility of simultaneous fluorescence immunophenotyping and fluorescence in situ hybridization study for the detection of estrogen receptor expression and deletions of the estrogen receptor gene in breast carcinoma cell lines.

For the first time, combined immunophenotyping and fluorescence in situ hybridization (FISH) technique according to the "fluorescence immunophenotyping and interphase cytogenetics as a tool for investigation of neoplasms" (FICTION) technique have been successfully applied in solid tumors. Thus, we were able to visualize the antigen expression of cells with chromosomal deletions of a tumor suppressor region directly. In six breast carcinoma cell lines, we investigated the correlation between estrogen receptor (ER) expression status and deletions of the estrogen receptor gene (ESR). To screen for deletions of the ESR gene, dual-color FISH was performed with a YAC (yeast artificial chromosome) probe containing the ESR gene and, as internal control, with a centromeric probe of chromosome 6. Deletions of the ESR gene were detected in four of six cell lines. For direct comparison of ER expression with the copy number of the ESR gene at the single cell level, immunophenotyping with mouse anti-human ER antibody was combined with FISH with the YAC probe containing the ESR gene according to the FICTION technique. There was no correlation between lack of or reduced ER expression and deletions of the ESR gene. One cell line with deletions of the ESR gene did express ER on the protein level, while another cell line without a deletion did not. Cells with deletions of the ESR gene were either ER expression positive or negative. The staining intensity of ER expression was not associated with the copy number of the ESR gene. Thus, this FICTION study unequivocally shows that deletions of the ESR gene are not the major cause of absent or reduced ER expression in breast carcinoma cell lines.

Animals↗

PubMed2000

Interaction between the LMWH reviparin and aspirin in healthy volunteers.

AIMS: To investigate potential interactions between reviparin and acetylsalicylic acid (ASA 300 mg o.d. from day 1-5). METHODS: In an open, randomized, three-way-cross over study nine healthy volunteers received reviparin (s.c. injection of 6300 anti-Xa units) or placebo from days 3 to 5 and acetylsalicylic acid (ASA 300 mg) or placebo from days 1 to 5. Assessments included bleeding time (BT), collagen (1 microg ml-1) induced platelet aggregation (CAG), heptest, plasma antifactor Xa-activity and activated partial thromboplastin time (aPTT). RESULTS: Median bleeding time at day 5 was 5.5 min after reverparin alone and after ASA alone and was 9.6 min after the combination of reviparin and ASA. ASA treatment reduced CAG from 84% to 40 to 50% of Amax; values after combined treatment of reviparin with ASA were not different from those after ASA alone. aPTT was prolonged to 32 s after reviparin; this effect was not modified if subjects received ASA. Combined treatment with ASA and reviparin had no effect on plasma anti-Xa-activity and heptest compared with reviparin alone. CONCLUSIONS: We could not entirely exclude a small interaction between reviparin and ASA on bleeding time, but the effect is probably without clinical significance.

Adult↗

PubMed2000

Ex vivo--in vitro interaction between aspirin, clopidogrel, and the glycoprotein IIb/IIIa inhibitors abciximab and SR121566A.

OBJECTIVES: To assess the interaction between aspirin and clopidogrel in healthy male volunteers and the interaction of the glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitors abciximab and SR121566A with blood from those pretreated subjects (ex vivo-in vitro). METHODS: Aspirin (300 mg/day), clopidogrel (75 mg/day), or the combination of both drugs were administered orally for 8 days. Group 1 (n = 5) started with aspirin and group 2 (n = 5) with clopidogrel. From day 4 to day 8, subjects of both groups received the combined treatment. Blood from these subjects was spiked with abciximab (0.5 and 1.5 microg x mL(-1)) and SR121566A (31 and 62 ng x mL(-1)). RESULTS: In vivo, average bleeding times were 6.8 minutes at baseline, 20.3 minutes for clopidogrel alone (P < .01), 10.9 minutes for aspirin alone (difference not significant), and 24.0 minutes (P < .01) for the combined treatment. Fibrinogen binding to the platelet GPIIb/IIIa receptor was reduced for aspirin to 69% (difference not significant), to 63% for clopidogrel (difference not significant), and to 63% for the clopidogrel plus aspirin combination (P < .01). CD62 expression as a marker of platelet granular secretion was reduced to 66% by clopidogrel (P < .01) and to 41% by the combination of clopidogrel and aspirin; aspirin alone had no effect. In vitro, with pretreatment with aspirin and clopidogrel, inhibitory effects of the GPIIb/IIIa inhibitors on fibrinogen binding were additive to changes observed with aspirin or clopidogrel alone. No effect on CD62 expression was observed with either GPIIb/IIIa inhibitor. Aspirin and clopidogrel reinforced effects of the GPIIb/IIIa inhibitors on adenosine diphosphate (5 micromol/L)-induced aggregation in an additive manner, a supra-additive effect was observed with collagen (2 microg x mL(-1))-induced aggregation. CONCLUSION: The augmentation of the antiaggregatory effects of GPIIb/IIIa inhibitors by aspirin and clopidogrel and the lack of antisecretory effects of GPIIb/IIIa inhibitors may favor their combination with clopidogrel.

Abciximab↗

PubMed2000

Effect of angiotensin II infusion with and without angiotensin II type 1 receptor blockade on nitric oxide metabolism and endothelin in human beings: a placebo-controlled study in healthy volunteers.

BACKGROUND: Angiotensin II has been shown to induce the synthesis of endothelium-derived relaxing factor nitric oxide (NO) and endothelin in vitro. In human beings, to our knowledge, no data on NO release in response to angiotensin II and on the influence of angiotensin II type 1 receptor blockade have been published. METHODS: In a placebo-controlled study in nine healthy volunteers, angiotensin II was administered intravenously for 6 hours with and without pretreatment with valsartan, a specific angiotensin II type 1 receptor antagonist. NO (NO2 + NO3) and endothelin plasma concentrations, clearance values for inulin and paraaminohippuric acid and NO (NO2 + NO3) excretion in urine were determined. RESULTS: During angiotensin II infusion NO plasma concentrations remained unaltered compared with placebo after 3 hours: 6.66 +/- 5.49 versus 5.56 +/- 3.09 micromol/L (P = ns) but increased after 6 hours: 18.36 +/- 20.02 versus 7.13 +/- 3.87 micromol/L (P < .04). The same was noted after pretreatment with valsartan: 7.61 +/- 5.69 versus 5.56 +/- 3.09 micromol/L (P= ns) after 3 hours, and 21.70 +/- 11.51 versus 7.13 +/- 3.87 micromol/L (P = .02) after 6 hours. In urine fractional NO excretion decreased after angiotensin II infusion: 0.87 +/- 0.72 versus 0.95 +/- 0.71 (P = .5) during the first 3 hours, and 0.44 +/- 0.39 versus 0.78 +/- 0.43 (P = .01) during the following 3 hours. After valsartan pretreatment the decrease in fractional urinary NO excretion began earlier: 0.40 +/- 0.15 versus 0.95 +/- 0.71 (P = .04) during the first 3 hours, and 0.17 +/- 0.11 versus 0.78 +/- 0.43 (P = .01) during the following 3 hours. Endothelin plasma concentrations showed no difference after angiotensin II infusion with or without valsartan. CONCLUSIONS: Our observations demonstrate for the first time that angiotensin II increases NO plasma concentrations in human beings and that this response is not mediated by angiotensin II type 1 receptor. In spite of increased NO plasma levels, urinary NO excretion decreased. Endothelin plasma levels remained unchanged during angiotensin II infusion.

Adult↗

PubMed2000

Juxtamembrane regions in the third intracellular loop of the thyrotropin-releasing hormone receptor type 1 are important for coupling to Gq.

Juxtamembrane residues in the putative third intracellular (I3) loops of a number of G protein-coupled receptors (GPCRs) have been shown to be important for coupling to G proteins. According to standard hydropathy analysis, the I3 loop of the mouse TRH receptor type 1 (mTRH-R1) is composed of 51 amino acids from position-213 to position-263. We constructed deletion and site-specific I3 loop TRH-R mutants and studied their binding and TRH-stimulated signaling activities. As expected, the effects of these mutations on TRH binding were small (less than 5-fold decreases in affinity). No effect on TRH-stimulated signaling activity was found in a mutant receptor in which the I3 loop was shortened to 16 amino acids by deleting residues from Asp-226 to Ser-260. In contrast, mutants with deletions from Asp-222 to Ser-260 or from Asp-226 to Gln-263 exhibited reduced TRH-stimulated signaling. In the region near transmembrane helix 6, single site-specific substitution of either Arg-261 or Lys-262 by neutral glutamine had little effect on signaling, but mutant TRH-Rs that were substituted by glutamine at both basic residues exhibited reduced TRH-stimulated activity. The reduced signaling activity of this doubly substituted mutant was reversed by over expressing the a subunit of Gq. These data demonstrate that the juxtamembrane regions in the TRH-R I3 loop are important for coupling to Gq.

Amino Acid Sequence↗

PubMed2000

Thrombolytics: drug interactions of clinical significance.

Thrombolytic agents activate plasminogen and induce a systemic fibrinolytic and anticoagulant state. Interaction of fibrinolysis with coagulation and platelet aggregation might be important for synergistic interactions with other antiplatelet or anticoagulant drugs. Thrombolytic agents are most often used in patients with coexisting cardiovascular medication, including various antihypertensives, beta-blocking agents, nitrates and aspirin (acetylsalicylic acid). In acute coronary syndromes, anticoagulants and antiplatelet compounds such as clopidogrel or glycoprotein IIb/IIIa receptor antagonists might be given. Inducers or inhibitors of the cytochrome P450 system are not reported to affect the pharmacokinetics of any thrombolytic agent. Since the elimination of the recombinant plasminogen activators saruplase and alteplase is dependent on liver blood flow, drugs affecting hepatic blood flow could theoretically affect the hepatic clearance of these agents. In fact, a reduction in thrombolytic activity has only been demonstrated for alteplase with nitroglycerin (glyceryl trinitrate). Pharmacodynamic interactions occur more often. The additive and beneficial effect of aspirin as concomitant therapy to thrombolysis has been demonstrated without excessive bleeding rates. No data are available on the interaction between ticlopidine or clopidogrel and thrombolytic agents in humans. Anticoagulation by heparin concomitantly with thrombolysis improves the patency rate of the occluded coronary vessel, but bleeding complications are seen more frequently. Although there has been no controlled study on the interaction between oral anticoagulants and thrombolytic agents, patients with myocardial infarction who were taking an oral anticoagulant before admission seem to be at higher risk for intracranial haemorrhage during thrombolytic therapy. Currently, no recommendations can be given for possible dose adjustment of thrombolytic therapy in patients receiving antiplatelet comedication. For comedication with heparin, it has been advised to monitor activated partial thromboplastin time frequently and to avoid values >2.5-fold normal. Patients receiving thrombolytic treatment should be monitored frequently for bleeding and the physician should be aware of any comedication exerting antiplatelet (e.g. aspirin, clopidogrel and ticlopidine) or anticoagulant (e.g. warfarin) effects.

Animals↗

PubMed2000

[Dose-response relationship: relevance for medical practice].

Dose-finding studies are performed routinely in patients and--if appropriate surrogate models exist--also in healthy volunteers. Such studies aim at establishing the optimal dose range for further clinical studies on the efficacy and the risk-benefit ratio of a new drug. The dose-response relationship of a drug is most often described by a sigmoidal curve. Its parameters include the mean effective dose, the maximal effect and the steepness. Interpretation of such curves should be done in the context of the intended clinical indications of the drug. The risk-benefit ratio of a drug can be assessed by overlapping the dose-response curve of wanted and unwanted clinical effects, again, any overlapping (which can be described e.g. by the therapeutic index) should be seen in the context of the indication and available therapeutic alternatives.

Adverse Drug Reaction Reporting Systems↗