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Biomedical subjects

K Alexander

Publications and source records attributed to K Alexander.

At least 127 records · Page 7Linked to original sources
PubMed1989

Lactate and pyruvate kinetics after treadmill exercise in patients with intermittent claudication.

Lactate and pyruvate movements in arterial and venous blood during recovery following treadmill exercise in 8 patients with arterial occlusive disease were studied by means of a two-compartment model. Blood lactate and pyruvate concentration curves over the recovery period were found to fit a two-exponential time function including a rapidly increasing and a slowly decreasing component. The velocity constants gamma 2 were dependent on the exercise load. The time of lactate disappearance during recovery decreased with the work load in patients with intermittent claudication. The velocity constant of the arterial blood pyruvate decrease was similar to that of the simultaneously measured lactate indicating that the rate of lactate removal is closely related to that of pyruvate. In conclusion, the use of the model allows to study factors likely to modify the coefficients, such as physical training, therapeutic effects and active recovery.

Adult↗
PubMed1989

[Interval exercise in arterial occlusive disease].

During intermittent exercise with periods of six minutes with two minutes pause the fluctuations in arterial and popliteal venous blood of lactate and pyruvate as well as changes in the lactate pyruvate ratio were studied in eleven patients with claudicatio intermittens. Oxygen uptake stabilizes itself within 4-6 min during exercise and VO2 at the end of an exercise period is higher than in the beginning of recovery. The level of arterial lactate does not vary significantly. The highest venous lactate was found in the pause. Significant differences in venous lactate, pyruvate and lactate pyruvate ratio were found between the first and second exercise. It is concluded that during intermittent exercise less glycogen was used and that this glycogen saving effect seems to have been accomplished both by a shift towards more oxidative metabolism and by a greater contribution from other substrates than glycogen.

Energy Metabolism↗
PubMed1988

Intermittent intraarterial infusion therapy with PGE1 in patients with severe claudication--results of a randomized prospective double blind study.

In a randomized prospective double blind study, intraarterial infusion therapy with prostaglandin E1 (PGE) was tested against infusion therapy with energy rich phosphates (ERP) in 40 patients with severe claudication. During the treatment period of three weeks, a significant increase of the painfree (PWD) and maximal walking distance (MWD) was observed. The improvement of PWD was of clinical relevance (PGE: 60----195 m; ERP: 69----170 m; p less than 0.001) and persisted during a 36 week post treatment observation period. The differences between the two drugs were not significant but showed a tendency in favour of the PGE therapy.

Alprostadil↗
PubMed1987

Properties of an Escherichia coli rhodanese.

A rhodanese enzyme of less than 20,000 molecular weight has been purified from Escherichia coli. The enzyme is accessible to substrates upon addition of whole cells to standard assay mixtures. This rhodanese has a Stokes radius of 17 A which for a globular protein corresponds to a molecular weight close to 14,000. It undergoes autoxidation to a polymeric form which is probably an inert dimer. Enzyme inactivated by oxidation can be reactivated by millimolar concentrations of cysteine. Steady-state initial velocity measurements indicate that the enzyme catalyzes the transfer of sulfane sulfur by way of a double displacement mechanism with formation of a covalent enzyme-sulfur intermediate. The turnover number for the enzyme-catalyzed reaction, with thiosulfate as donor substrate and cyanide ion as the sulfur acceptor, is 260 s-1. This value corresponds to a catalytic efficiency 60% of that measured for a previously characterized bovine liver enzyme of more than twice the molecular weight. Furthermore, KmCN is 24 mM which is 2 orders of magnitude higher than the value observed previously for the bovine enzyme. Evidence from chemical inactivation studies implicates an essential sulfhydryl group in the enzyme activity. It is proposed that this group is the site of substrate-sulfur binding in the obligatory enzyme-sulfur intermediate. Furthermore, a cationic site important for binding of the donor thiosulfate is tentatively identified from anion inhibition studies. Tests of alternate acceptor substrates indicate that the physiological dithiol, dihydrolipoate, is a more efficient acceptor than cyanide ion for the enzyme-bound sulfur. Of possibly greater physiological significance, it has been found that the enzyme catalyzes the formation of iron-sulfur centers. Other work indicates the E. coli rhodanese is subject to catabolite repression and suggests a physiological role for the enzyme in aerobic energy metabolism.

Anions↗
PubMed1987

The inhibition of cytochrome oxidase by diaminomaleonitrile.

Diaminomaleonitrile, a tetramer of cyanide, was examined as a possible antagonist to cyanide inhibition of cytochrome oxidase (EC 1.9.3.1). This compound was found to inhibit cytochrome oxidase in vitro; however, despite their structural similarities, diaminomaleonitrile and cyanide inhibit cytochrome oxidase by different mechanisms and bind to the enzyme at different sites. Diaminomaleonitrile inhibition of cytochrome oxidase is described in terms of a partially competitive mechanism. Biological oxidation of diaminomaleonitrile may lead to the formation of cyanide.

Animals↗
PubMed1987

Comparison of Laser-Doppler-Flux and tcPO2 in healthy probands and patients with arterial ischemia.

Transcutaneous PO2 (tcPO2) and Laser-Doppler-Flux (LDF) were compared on the dorsum of the foot in 20 healthy probands and 35 patients with peripheral arterial occlusive disease at clinical stage II b or IV. The probes were kept at a temperature of 37 degrees C. Using different procedures, we brought about dynamic changes and compared the reaction of the two signals. Venous occlusion resulted in a decrease of both signals to a similar extent in both groups. During leg dependency both signals decreased in the probands suggesting a normal vasoconstrictor response. In most of the patients an increase was observed, but some showed a decrease even at clinical stage IV. LDF had a stronger tendency towards a decrease. On leg elevation, LDF slightly increased in probands and decreased in patients. Here, the tendency towards a decrease was higher for tcPO2. After arterial occlusion reactive hyperemia was more pronounced in probands. Differences between tcPO2 and LDF seem to be mainly due to the different capillary systems contributing to the signal.

Adult↗
PubMed1987

[Comparative studies of the diagnostic value of various parameters of Doppler frequency spectral analysis of the carotid artery].

Angiographic findings in 94 internal carotid arteries were compared to different parameters of Doppler frequency spectral analysis: systolic and late diastolic peak frequency of the internal carotid artery, ratio of the internal and common carotid systolic and late diastolic peak frequency, spectral broadening as calculated by subtracting internal carotid mean frequency from systolic or late diastolic peak frequency respectively. The normal values were calculated as the 97.5% confidence interval of these parameters in angiographically normal vessels. Specificity, sensitivity, overall accuracy and negative as well as positive predictive value were also calculated. The diagnostic value of the systolic peak frequency of the internal carotid artery proved not to be exceeded by any of the other parameters.

Arterial Occlusive Diseases↗