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Biomedical subjects

M Ritter

Publications and source records attributed to M Ritter.

At least 217 records · Page 12Linked to original sources
PubMed1985

The effect of methotrexate pretreatment on 5-fluorouracil kinetics in sarcoma 180 in vivo.

Synergy of sequential MTX and 5-FU has been shown in several in vitro and in vivo systems. In the present study the influence of time interval between MTX and 5-FU and MTX dose on 5-FU accumulation in tumor cells has been examined in Sarcoma 180 in vivo. There was a clear relationship between MTX dose applied and amount of 5-FU detected in the acid-soluble fraction, the RNA fraction and the thymidylate synthase complex fraction. Also, the MTX-5-FU time interval affected clearly the amount of 5-FU detected in all three fractions, the optimum time interval being 8-12 hr. The results indicate that for sequential application of MTX and 5-FU selection of an adequate MTX dose and a sufficient time interval is crucial to achieve synergistic action.

Animals↗
PubMed1985

Regulation of T-cell receptor gene expression in human T-cell development.

A cDNA clone encoding the alpha chain of the human T-cell antigen receptor was isolated by screening a library from the human T-cell line Jurkat with a mouse alpha-chain cDNA clone. This human alpha-chain clone, together with a human antigen receptor beta-chain cDNA clone, was used to determine the stage of T-cell development at which antigen receptor mRNAs first appear. Blot-hybridization analysis of mRNA isolated from a panel of human thymic tumor lines clearly demonstrated that beta-chain transcripts could be detected in all T-lineage cells. However, alpha-chain transcripts were only found in the most phenotypically mature lines, which express the antigen receptor-associated molecule T3. Furthermore, beta-chain transcripts were abundant in RNA prepared from purified T3-negative thymocytes, whereas alpha-chain transcripts were virtually absent. From these results we conclude that alpha-chain expression occurs later in thymic ontogeny than that of the beta chain and propose that it controls surface expression of the antigen receptor-T3 complex.

Amino Acid Sequence↗
PubMed1984

Pulsus alternans: its influence on systolic and diastolic function in aortic valve disease.

Left ventricular high fidelity pressure measurements and simultaneous biplane cineangiocardiography were performed in 12 patients with severe aortic valve disease (aortic stenosis in 10, aortic insufficiency in 1 and combined valve lesion in 1). Left ventricular contractility was estimated from maximal rate of left ventricular pressure rise (max dP/dt), peak measured velocity of contractile element shortening (Vpm) and mean circumferential fiber shortening velocity. Left ventricular relaxation was assessed in 12 patients from the time constant (T) of the decline in left ventricular pressure; this constant was calculated from a nonlinear regression analysis of pressure and time (method 1) and a linear regression analysis of pressure and negative dP/dt (method 2). Left ventricular diastolic function was evaluated in nine patients from simultaneous diastolic pressure-volume relations during the strong and weak beats. During pulsus alternans, heart rate and left ventricular end-diastolic pressure remained unchanged, whereas peak systolic pressure (220 versus 204 mm Hg, p less than 0.01) and end-systolic pressure (101 versus 95 mm Hg, p less than 0.01) were significantly higher during the strong beat than during the weak beat. Max dP/dt was alternating (2,162 versus 1,964 mm Hg, p less than 0.05), whereas the peak velocity of contractile element shortening remained unchanged (1.21 versus 1.18 ML/s). Systolic shortening of the left ventricular minor axis was significantly (p less than 0.02) greater during the strong (24%) than during the weak (19%) beat, but that of the left ventricular major axis remained essentially unchanged (8 versus 7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Effects of the tetracyclic antidepressant pirlindole on sensorimotor performance and subjective condition in comparison to imipramine and during interaction of ethanol.

Two experiments were designed to investigate the side-effects on motor performance of the new tetracyclic antidepressant, pirlindole, in healthy volunteers. First, pirlindole was compared with imipramine and placebo. In the second study the interaction of pirlindole with a small amount of ethanol (0.4 g 17 vol%/kg) was analysed. Ratings of subjective feelings and measurements of sensorimotor performance (simple and choice reaction, tracking) of the pirlindole-treated group did not differ from those of the placebo group, whereas imipramine caused a change of the subjective condition to more lethargy and a greater delay of the simple reaction time. The effects of pirlindole proved to be unaffected by ethanol.

Adult↗
PubMed1984

Diastolic stiffness and myocardial structure in aortic valve disease before and after valve replacement.

Passive diastolic properties were determined in 10 control patients and 21 patients with aortic valve disease before and 17.5 months after successful valve replacement. Ten patients had severe aortic stenoses (AS), five had combined aortic valve lesions (AS + aortic insufficiency [AI]), and six patients had severe AI. Left ventricular endomyocardial biopsies were obtained before and after surgery in patients with AS, AS + AI, and AI. Simultaneous echocardiographic and high-fidelity pressure measurements were made in all patients, and left ventricular chamber stiffness was calculated from a viscoelastic pressure-circumference relationship and left ventricular myocardial stiffness from a viscoelastic stress-strain relationship. The constant of chamber stiffness, beta', was slightly although not significantly increased in patients with AS (0.27 before and 0.24 after surgery), but was normal in those with AS + AI (0.22 before and 0.17 after surgery) and slightly decreased in those with AI (0.18 before and 0.16 after surgery) when compared with in control subjects (0.21). The constant of myocardial stiffness beta was normal in patients with AS (13.2), AS + AI (11.5), and AI (11.7) before surgery compared with in the control group (12.5). beta increased, however, significantly in those with AS (25.2; p less than .02), but not in those with AS + AI (16.3; NS) and AI (12.8; NS) after surgery. Myocardial morphologic characteristics showed a significant decrease in muscle fiber diameter in patients with AS, AS + AI, and AI, as well as a significant increase in interstitial fibrosis from 15% to 26% (p less than .05) in those with AS and a slight increase from 15% to 22% (NS) in those with AS + AI and from 19% to 24% (NS) in those with AI. Left ventricular fibrous content (left ventricular muscle mass index multiplied by interstitial fibrosis) remained, however, unchanged in all three groups after aortic valve replacement. In conclusion, left ventricular chamber stiffness is increased in AS but decreased in AI, whereas LV myocardial stiffness is normal in patients with aortic valve disease before surgery. After surgery, left ventricular myocardial stiffness increased significantly in AS patients but remained unchanged in those with AI. Postoperative changes in myocardial structure were characterized by a decrease in muscle fiber diameter and a relative increase in interstitial fibrosis, whereas fibrous content remained unchanged. Thus, regression of myocardial hypertrophy in aortic valve disease is accompanied by an increase of myocardial stiffness in concentric hypertrophy that is not seen in eccentric hypertrophy.

Adult↗
PubMed1984

Diastolic function in aortic valve disease: techniques of evaluation and pre-/postoperative changes.

Passive diastolic properties of the left ventricle are determined by several factors intrinsic or extrinsic to the ventricle. In patients with myocardial hypertrophy due to longstanding pressure or volume overload increased muscle mass and structural alterations of the myocardium are responsible for changes in passive elastic properties. Evaluation of diastolic function includes determination of ventricular (= chamber) and myocardial (= muscle) stiffness from simultaneous pressure-volume and stress-strain relations during passive diastolic filling. The slope of the pressure-volume relationship is equal to the constant of chamber stiffness and the slope of the stress-strain relationship equal to the constant of myocardial stiffness. Passive diastolic properties were determined in ten control patients and 21 patients with aortic valve disease before and 17.5 months after successful valve replacement. Ten patients presented with severe aortic stenosis, five patients with combined valve lesions and six patients with severe aortic insufficiency. Simultaneous high-fidelity pressure measurements and M-mode echocardiography were carried out in all patients. Myocardial stiffness was calculated from a viscoelastic stress-strain relationship using a nonlinear curve-fit program. Standard hemodynamic measurements showed a significant decrease in pressure and volume overload after successful valve replacement. Left ventricular muscle mass index decreased in all three groups significantly after surgery, whereas systolic ejection fraction remained unchanged pre-/postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Stenosis, Subvalvular↗
PubMed1984

Effect of sample dilution on measurements of free (unbound) hormones.

We describe the influence of sample dilution on the measurement of free or non-protein-bound hormones in serum or plasma. The concentration of free hormone in the sample will alter after dilution or addition of binding reagents. The extent of this equilibrium perturbation depends on the binding properties of the endogenous carrier proteins, which vary from sample to sample and from sample to reference standard. As examples, we demonstrate the different changes in concentrations of free thyroxin and free cortisol after dilution, both experimentally and by theoretical modeling of the hormone-protein distribution. We also show how this systematic error can be minimized in the design of free hormone assays.

Carrier Proteins↗
PubMed1983

On the validity of free hormone measurements.

The influence of equilibrium perturbation on the measurement of free or non-protein-bound hormones in serum or plasma is described. The free analyte concentration in the sample will alter after dilution or addition of binding reagents. The extent of this perturbation is not constant. It depends on the binding properties of the endogenous carrier proteins which vary from sample to sample and from sample to reference standard. As examples, the different changes of the free thyroxine and free cortisol concentrations after dilution are demonstrated both experimentally and by theoretical modeling of the hormone-protein distribution. It is shown how this systematical error can be minimized in the design of free hormone assays.

Carrier Proteins↗
PubMed1983

46,XX/46,XY chimerism in a phenotypically normal man.

Some twenty cases of dispermic chimeras with the karyotype 46,XX/46,XY, discovered because of gonadal dysplasias or a true hermaphroditism, have been reported. This is a report of a phenotypically normal man with 46,XX/46,XY chimerism in whom a prepubertal finding of positive X-chromatin was interpreted as Klinefelter syndrome. The diagnosis was revised 11 years later when the family doctor, who doubted the earlier diagnosis because of the patient's normal-sized testes, sent him to an outpatient clinic. The young man was 23 years old, athletic (74kg, 180cm), with normal body proportions, normal sexual hair distribution, normal libido and potency, normal endocrine parameters, and a normal spermiogram. The karyotype revealed an XX/XY mosaic in a proportion of 1:2. An identical set of maternal markers (Q- and C-banding) was present in male and female cells. Differences were found with respect to two paternal markers. Furthermore, blood, serum, and red cell enzyme groups in five systems showed two phenotypes, again with duality of paternal origin. It is concluded that a positive X-chromatin in prepuperty, especially in the absence of supporting clinical features, must be followed by a karyotype study.

Adult↗
PubMed1983

Anthracene-9-carboxylic acid inhibits renal chloride reabsorption.

From previous studies, it is known that in the diluting segment, C1- -ions are transported from the tubule lumen into the cell together with Na+ and K+ via a furosemide-sensitive cotransport system. This carrier-mediated process, located in the luminal cell membrane, is driven by the steep "downhill" Na+ gradient (directed from lumen to cell) which is maintained by the ouabain-sensitive Na+/K+-pump at the peritubular cell membrane. C1- -ions are accumulated within the cell cytosol and are supposed to leave the cell by a C1- -conductive pathway. The present experiments, performed in diluting segments of the isolated perfused frog kidney, demonstrate the existence of a significant C1- -permeability of the peritubular cell membrane and its complete inhibition by anthracene-9-COOH. The data indicate that C1- -reabsorption can be reduced not only by the inhibition of luminal C1- -entry (i.e. by furosemide) but also by the blockade of the passive C1- -exit step across the peritubular cell membrane. Since complete inhibition of C1- -permeability reduces transepithelial uphill C1- -transport only to half, the data disclose the existence of an additional C1- -pathway at the peritubular cell membrane.

Animals↗
PubMed1982

Nickel requirement of Acetobacterium woodii.

Growth of Acetobacterium woodii on H2 and CO2 rather than on fructose was dependent on nickel. Nickel-deprived cultures growing on fructose did not synthesize acetate from CO2; under these conditions hydrogen formation was used as the electron sink. The data indicate that nickel is involved in CO2 reduction to acetate in A. woodii.

Acetates↗