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Biomedical subjects

J Schaefer

Publications and source records attributed to J Schaefer.

At least 127 records · Page 7Linked to original sources
PubMed1984

Relationships between beat-to-beat interval and the strength of contraction in the healthy and diseased human heart.

Twenty-six adult patients, classified by clinical and catheter criteria into groups of those with normal and abnormal left ventricular function, were studied during cardiac catheterization. Right heart pacing was established, and left ventricular dP/dt was measured with end-catheter manometers. By varying the interval preceding a test beat after periods of steady pacing it was confirmed that recovery of left ventricular mechanical function (maximum dP/dt) occurs approximately 800 msec (optimum interval) after a beat. The augmentation of maximum dP/dt of the first 2 beats after an extrasystole, each spaced at the optimum interval, was also studied; the amount of potentiation was varied by alterations in extrasystolic interval. Potentiation decayed from the first to the second postextrasystolic beat with a ratio that was fixed in each individual patient. The ratio (recirculation fraction) was higher in patients with normal than in those with abnormal left ventricular function (mean +/- SD 0.52 +/- 0.10 vs 0.37 +/- 0.11, p less than .005). There was an inverse relationship between this ratio and the degree of potentiation of the first postextrasystolic beat (r = .80, p less than .001). We postulate a disturbance of excitation-contraction coupling mechanisms to explain these effects.

Adult↗
PubMed1983

Direct measurement of peptidoglycan cross-linking in bacteria by 15N nuclear magnetic resonance.

Cross-polarization magic angle spinning 9.12-MHz 15N nuclear magnetic resonance was used to measure the extent of peptidoglycan cross-linking within intact bacterial cells and isolated cell walls of Aerococcus viridans ATCC 10400 grown in the presence of L-[epsilon-15N]lysine. A value of 49% for the cross-linking index was found for normal cells, while for those grown in the presence of low levels of penicillin G (0.1 micrograms/ml), the cross-linking index was reduced to 35%.

Magnetic Resonance Spectroscopy↗
PubMed1983

Lipid bilayer dynamics and rhodopsin-lipid interactions: new approach using high-resolution solid-state 13C NMR.

High-resolution, solid-state 13C NMR spectra have been obtained for unsonicated multilamellar dispersions of 1,2-dilauryl-sn-glycero-3-phosphocholine (DLPC), recombinant membranes containing DLPC and rhodopsin, and native retinal rod disk membranes. The roles of 1H dipolar decoupling, 1H-13C cross-polarization, and magic-angle sample spinning have been investigated. Rotating-frame 13C relaxation times have been measured and are discussed in terms of lipid bilayer dynamics and rhodopsin-lipid interactions.

Fatty Acids, Unsaturated↗
PubMed1983

Electrical and mechanical restitution of the human heart at different rates of stimulation.

Action potential duration and contractility are reduced following premature excitations, and gradually increase as the stimulus interval is lengthened. To examine these phenomena of electrical and mechanical restitution in the human heart, we simultaneously measured action potential duration and the maximum rate of left ventricular pressure in five patients undergoing electrophysiological study. Test beats were introduced at varying intervals after the last of a series of steady state intervals. By plotting action potential duration and maximum rate of left ventricular pressure as a function of the test interval, we formed electrical and mechanical restitution curves. When the rate of steady state pacing was increased, there was a decrease in action potential duration and an increase in the maximum rate of left ventricular pressure for all test intervals; i.e., a change in pacing rate affected action potential duration and maximum rate of left ventricular pressure of test responses in a reciprocal fashion. In addition, a higher steady state pacing rate allowed action potentials and contractile responses to be elicited at shorter test intervals, thereby displacing the electrical and mechanical restitution curves to the left. The magnitude of the leftward shift of both curves corresponded closely to the shortening of the steady state action potential duration induced by the increase in pacing rate. These findings confirm for the human heart that both electrical and mechanical restitution occur after membrane repolarization, i.e., as a function of the electrical diastolic interval preceding a beat, and not the stimulus interval.

Action Potentials↗
PubMed1982

A microagglutination test for human Brucella canis antibodies.

A microagglutination test for the detection of Brucella canis antibodies in humans is described. The use of safranin-dyed B. canis organisms as antigen gave easily interpretable settling patterns and reproducible endpoints. The finding of 18 of 1,147 sera with titers greater than or equal to 1:160 resulted in a presumed false-positive rate of 1.6%. Repeat testing of these positive sera in diluent to which 0.6 m NaCl had been added showed a decrease in titer to less than or equal to 1:40 in eight. Conversely, the increased salt concentration permitted detection of blocking antibodies in two sera which were originally thought to be negative. The test provided serologic evidence for B. canis infection in four patients with otherwise undiagnosed febrile illness. The disease is underdiagnosed due to general lack of serologic testing facilities and misconceptions concerning its prevalence.

Agglutination Tests↗
PubMed1982

[N]NMR determination of asparagine and glutamine nitrogen utilization for synthesis of storage protein in developing cotyledons of soybean in culture.

Solid-state [(15)N]NMR was used to measure the use of the amide and amino nitrogens of glutamine and asparagine for synthesis of storage protein in cotyledons of soybean (Glycine max L. cv. Elf) in culture. No major discrimination in the incorporation of the amide or amino nitrogens of glutamine into protein is apparent, but the same nitrogens of asparagine are used with a degree of specificity. During the first seven days in culture with asparagine as the sole nitrogen source, the amino nitrogen donates approximately twice as much nitrogen to protein as does the amide nitrogen. The use of the amide nitrogen increases with longer periods of culture. The reduced use of the amide nitrogen was confirmed by its early appearance as ammonium in the culture medium. The amide nitrogen of asparagine was found at all times to be an essential precursor for protein because of its appearance in protein in residues whose nitrogens were not supplied by the amino nitrogen. In addition, methionine sulfoximine inhibited growth completely on asparagine, indicating that some ammonium assimilation is essential for storage protein synthesis. These results indicate that in a developing cotyledon, a transaminase reaction is of major importance in the utilization of asparagine for synthesis of storage protein and that, at least in the early stages of cotyledon development, reduced activities of ammonium-assimilating enzymes in the cotyledon tissue or in other tissues of the seed or pod may be a limiting factor in the use of asparagine-amide nitrogen.

Journal Article↗
PubMed1982

N- and [C]NMR determination of utilization of glycine for synthesis of storage protein in the presence of glutamine in developing cotyledons of soybean.

Solid-state (15)N- and [(13)C] NMR have been used to measure quantitatively the utilization of glycine in the presence of glutamine for the synthesis of storage protein in immature cotyledons of soybean (Glycine max L. cv. Elf) in culture. The presence of an equal molar amount of glycine in the medium causes a decrease in the use of glutamine-amide nitrogen. Glycine nitrogen is incorporated extensively into peptide bonds (in amounts greater than what would be expected if it appeared solely in glycine residues), but is used sparingly for synthesis of histidine ring residues, guanidino nitrogen residues of arginine, and lysine residues. The modest use of glycine carbon in protein synthesis does not parallel the use of glycine nitrogen.

Journal Article↗
PubMed1982

Human brucellosis caused by Brucella canis: clinical features and immune response.

Human infection by Brucella canis is not often recognized due to a lack of serious consideration of the disease as a diagnostic possibility. Another factor is the limited availability of specific serologic tests needed in the absence of cross-reactivity between antibodies to B. canis and other Brucella pathogenic to humans. In addition, the organism may not be isolated from blood culture, particularly after antibiotic therapy. We report clinical and laboratory features of four patients with serologically diagnosed B. canis infection and point out the importance of specific serologic testing for B. canis when brucellosis is a diagnostic possibility.

Adult↗
PubMed1981

Estimation of protein turnover in soybean leaves using magic angle double cross-polarization nitrogen 15 nuclear magnetic resonance.

Magic angle cross-polarization 15N nuclear magnetic resonance spectra of intact lyophilized soybean leaves have been obtained at 9.12 MHz. The leaves were harvested over a 6-week period from 15N-uniformly labeled plants exposed to 13CO2 for 1 to 7 days. The concentration of 13C-15N double labels in the main chains of leaf protein was determined nondestructively by double cross-polarization techniques. Both incorporation and turnover rates of these double labels were estimated and together lead to the conclusion that the protein of a mature, fully expanded soybean leaf is fairly long lived, with a half-life of about 30 days.

Kinetics↗
PubMed1981

Comparison of ftorafur with 5-fluorouracil in combination chemotherapy of advanced gastrointestinal carcinoma.

The aim of the study was to compare the combination 5-FU-carmustine with ftorafur-carmustine in the treatment of advanced gastrointestinal cancer. To this end, a prospective, multicenter, randomized trial was initiated. Part I of this trial showed that similar response rates can be obtained with 5-FU-carmustine and ftorafur-carmustine in 109 patients (32.7% versus 26.3%). However, median survival was better in patients treated with 5-FU-carmustine (307 days versus 163 days). Part II of the trial revealed that neither a higher dosage of ftorafur (2 g/m2/day X 5 days) nor the addition of vincristine to both regimens changed the previously obtained results significantly. Again, median survival was found to be better in patients treated with 5-FU combination chemotherapy (304 days versus 144 days). Both the 5-FU and the ftorafur combination were tolerated reasonably well. The results suggest that combination chemotherapy including 5-FU is superior to ftorafur at the applied dosages in terms of survival.

Adult↗
PubMed1981

Different repetition frequencies of a 120 base-pair DNA-element and its arrangement in Chironomus thummi thummi and Chironomus thummi piger.

THe repetition frequency of a highly repetitive DNA sequence has been measured in the genomes of Ch. thummi thummi and Ch, th, piger. This sequence is known to be involved in the evolutionary duplication of defined chromosomal segments leading to a significant increase in the genome size of Ch. th. thummi. Reassociation of this highly repetitive DNA sequence which has a repeat length of 120 base-pairs, with total Ch. th. thummi and Ch. th. piger DNA has shown that the repetition frequency in the Ch, th, thummi DNA is 5.5 fold higher than in Ch, th piger. In both genomes a 120 base-pair sequence is present as tandemly repeated sequence as shown by Southern analysis.

Animals↗
PubMed1981

Asparagine amide metabolism in developing cotyledons of soybean.

Magic-angle single and double cross-polarization (13)C and (15)N NMR spectra have been obtained of lyophilized soybean cotyledons cultured on media containing, as the only nitrogen source, [4-(13)C, amide-(15)N]asparagine. Single cross-polarization NMR shows directly and unambiguously that both labels from asparagine are incorporated extensively and nonrandomly into protein by the developing cotyledon during a 2-week period. A stable-isotope double label tags a chemical bond. The metabolic fate of the asparagine double label was followed by double cross-polarization NMR using the latter's sensitivity to the dipolar coupling between directly bonded (13)C and (15)N. These experiments show that in culture the direct incorporation of asparagine (with no scrambling of label) accounts for about half of all asparagine residues in soybean protein. This conclusion implies the operation of a regulatory apparatus in soybeans for both direct utilization and degradation of asparagine in protein synthesis.

Journal Article↗
PubMed1980

Simultaneous recording of monophasic action potentials and contractile force from the human heart.

Cardiac monophasic action potentials (MAPs) and contractility have been simultaneously measured in man while the heart rate was being changed by right atrial pacing. A new non-suction electrode was used for safe and long-term recording of MAPs from the endomyocardium. Abrupt changes in cycle-length were followed first by a fast, then a slow response in the adaptation of MAP-duration and of contractility (LV dp/dt max) to the new steady state. After increasing the heart rate then slow phase of MAP shortening appears to be related to the slow staircase of contractility, whereas after the step decrease of frequency no such a relation could be observed. The consistency of these results with those obtained in corresponding in-vitro experiments indicates that this methodical approach may be suitable for assessing the process of E-C coupling in the human heart.

Action Potentials↗
PubMed1980

Characterization of photorespiration in intact leaves using carbon dioxide labeling.

The (13)C nuclear magnetic resonance spectra of sucrose extracted from intact soybean and corn leaves labeled with (13)CO(2) for 5 to 180 minutes have been obtained at 22.6 megahertz. The spectra provide a direct determination of the relative concentrations of (12)C-(13)C and (13)C-(13)C pairs of carbons in the labeled triose components of sucrose. This distribution of label is strongly dependent on the O(2) concentrations used during labeling for soybean but not for corn. Based on the time dependence of the experimental labeling patterns, photorespiration in air appears to be a sizable fraction of the apparent photosynthetic rate for soybean, but not for corn.

Journal Article↗