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Biomedical subjects

M Alam

Publications and source records attributed to M Alam.

At least 199 records · Page 11Linked to original sources
PubMed1991

Structural features of methyl-accepting taxis proteins conserved between archaebacteria and eubacteria revealed by antigenic cross-reaction.

A number of eubacterial species contain methyl-accepting taxis proteins that are antigenically and thus structurally related to the well-characterized methyl-accepting chemotaxis proteins of Escherichia coli. Recent studies of the archaebacterium Halobacterium halobium have characterized methyl-accepting taxis proteins that in some ways resemble and in other ways differ from the analogous eubacterial proteins. We used immunoblotting with antisera raised to E. coli transducers to probe shared structural features of methyl-accepting proteins from archaebacteria and eubacteria and found substantial antigenic relationships. This implies that the genes for the contemporary methyl-accepting proteins are related through an ancestral gene that existed before the divergence of arachaebacteria and eubacteria. Analysis by immunoblot of mutants of H. halobium defective in taxis revealed that some strains were deficient in covalent modification of methyl-accepting proteins although the proteins themselves were present, while other strains appeared to be missing specific methyl-accepting proteins.

Archaea↗
PubMed1991

Rotation and switching of the flagellar motor assembly in Halobacterium halobium.

Halobacterium halobium swims with a polarly inserted motor-driven flagellar bundle. The swimming direction of the cell can be reserved by switching the rotational sense of the bundle. The switch is under the control of photoreceptor and chemoreceptor proteins that act through a branched signal chain. The swimming behavior of the cells and the switching process of the flagellar bundle were investigated with a computer-assisted motion analysis system. The cells were shown to swim faster by clockwise than by counterclockwise rotation of the flagellar bundle. From the small magnitude of speed fluctuations, it is concluded that the majority, if not all, of the individual flagellar motors of a cell rotate in the same direction at any given time. After stimulation with light (blue light pulse or orange light step-down), the cells continued swimming with almost constant speed but then slowed before they reversed direction. The cells passed through a pausing state during the change of the rotational sense of the flagellar bundle and then exhibited a transient acceleration. Both the average length of the pausing period and the transient acceleration were independent of the stimulus size and thus represent intrinsic properties of the flagellar motor assembly. The average length of the pausing period of individual cells, however, was not constant. The time course of the probability for spontaneous motor switching was calculated from frequency distribution and shown to be independent of the rotational sense. The time course further characterizes spontaneous switching as a stochastic rather than an oscillator-triggered event.

Flagella↗
PubMed1991

Left ventricular function immediately after exercise in elite cyclists.

To determine the response to exercise of the left ventricle of endurance-trained athletes, 6 elite (world class) cyclists were compared to 6 untrained healthy control subjects. In athletes the stroke volume increased with exercise. In untrained volunteers the stroke volume did not change with exercise. This difference of the response of the stroke volume to exercise reflected a difference of the left ventricular end-diastolic volume. In athletes the left ventricular end-diastolic volume tended to increase. In control subjects the end-diastolic volume decreased. In conclusion, athletes increased cardiac output by increasing stroke volume and heart rate, whereas control subjects increased their cardiac output only by increasing their heart rate.

Adolescent↗
PubMed1991

Transthoracic and transesophageal echocardiography in the diagnosis and surgical management of right atrial myxoma.

An asymptomatic patient was discovered to have a large right atrial myxoma by transthoracic echocardiography. Preoperative considerations included the possibility of satellite lesions, left atrial origin, and a question of tricuspid valve involvement. Subsequent operative transesophageal echocardiography demonstrated single-stalk attachment in the right atrial septal wall and no satellite lesions. Doppler and color flow examination immediately following tumor removal aided in the decision not to perform tricuspid annuloplasty as there was no significant tricuspid regurgitation. The combined use of transthoracic and transesophageal echocardiography with Doppler and color flow imaging aids in the preoperative and intraoperative diagnosis and surgical management of right atrial tumors.

Echocardiography↗
PubMed1991

The role of echocardiography in acute myocardial infarction.

Our institutional experience with two-dimensional echocardiography and color flow Doppler tests, as well as a review of the literature, reveals that echocardiography is useful in diagnosing myocardial infarction. Furthermore, complications of myocardial infarction such as mitral regurgitation with or without papillary muscle rupture, acquired ventricular septal defect, true and false left ventricular aneurysms, left ventricular thrombi, right ventricular infarction, and pericardial effusion in the setting of acute infarction can be detected by cardiac ultrasound. Echocardiography is also useful in assessing prognosis of postinfarction patients based on degree of left ventricular dysfunction. This test, however, is not 100% sensitive and specific in diagnosing these entities and should be reviewed in context of a patient's history, physical findings, and other laboratory tests.

Echocardiography↗
PubMed1991

Effects of exercise on the displacement of the atrioventricular plane in patients with coronary artery disease. A new echocardiographic method of detecting reversible myocardial ischaemia.

The effect of exercise on the displacement of the atrioventricular (AV) plane was studied by echocardiography (echo) in 48 patients with stable angina pectoris without prior myocardial infarction and 20 age-matched healthy subjects. Echo was performed at rest, immediately after and 10 and 30 min after the test. The patients also underwent thallium stress scintigraphy and coronary angiography. From the apical four- and two-chamber views, the atrioventricular plane displacement (AVPD) during the cardiac cycle was recorded at four sites corresponding to the septal, anterior, lateral and posterior walls of the left ventricle and a mean value was calculated (AV-mean). The healthy subjects and patients had almost the same AVPD at all the sites at rest (AV-mean of 14.5 and 14.2 mm respectively). Immediately post-exercise the healthy subjects showed a significant (P less than 0.001) and equally distributed increase in the AVPD at all the sites with an AV-mean value of 19.2 mm. In most of the patients with angiographically confirmed coronary artery disease (CAD), there was a reversible decrease of AVPD (greater than or equal to 3 mm) at one or more of the AV plane sites. The overall sensitivity and specificity were 80% and 100% respectively in identifying CAD patients. The changes correlated well with the reversible ischaemic changes on the thallium scan (sensitivity, 88%, and specificity, 83%). A generalized exercise-induced decrease in AVPD at all the recorded sites had a high specificity (91%) in detecting patients with three-vessel disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Virus burden in human immunodeficiency virus type 1-infected children: relationship to disease status and effect of antiviral therapy.

The human immunodeficiency virus type 1 (HIV-1) was isolated from the plasma and peripheral blood mononuclear cells (PBMCs) from each of 21 infected children. The mean titers in plasma were 7 and 165 tissue culture-infective doses per milliliter in 9 children with asymptomatic (P-1) and 12 with symptomatic (P-2) infection, respectively (P = .0013). Significantly higher viral titers were found in PBMCs obtained from P-2 compared with P-1 children: 1920 vs 25 tissue culture-infective doses per 10(6) PBMC (P = .0018). In symptomatic patients at least 1 in 520 circulating mononuclear cells harbored HIV-1. No correlation was found between the viral burden and CD4+ lymphocyte counts. A decrease in the HIV-1 titers was noted both in PBMCs and plasma of symptomatic patients treated with zidovudine for 2 to 7 months. It is concluded that symptomatic children harbor a higher amount of the virus in plasma and PBMCs than asymptomatic children. Zidovudine treatment for 2 months or more decreased the amount of HIV-1 in PBMCs and plasma.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Isolation, synthesis, and evaluation of a series of indencarbazates as hypotensive agents.

Two indencarbazates, 1 and 2, were isolated from the sponge Cliona caribboea. These compounds were found to possess mild hypotensive activity. A series of analogues of 1 was synthesized in order to study the structure-activity relationship of this unique class of compounds. A variety of structural changes did not result in a consistent pattern of biological activity.

Animals↗
PubMed1990

Atrioventricular plane displacement in severe congestive heart failure following dilated cardiomyopathy or myocardial infarction.

Echocardiographic recording of the atrioventricular (AV) plane displacement during the cardiac cycle was used to assess left ventricular (LV) global function in patients with congestive heart failure (CHF). The study population consisted of 70 patients with chronic CHF (NYHA functional groups III and IV) following dilated cardiomyopathy (DCM) or myocardial infarction (MI), and 35 age-matched healthy subjects. The AV plane displacement was recorded from the apical 4- and 2-chamber views at four LV sites located about 90 degrees apart and representing the septal, anterior, lateral and posterior parts of the LV wall. A mean value was calculated from the above sites (AV-mean). Patients with CHF showed a significant generalized reduction of AV plane displacement compared to healthy subjects (5.6 mm vs. 14.5 mm, P less than 0.001). Thirty CHF patients also underwent radionuclide angiography in order to determine the ejection fraction (EF). The correlation between AV-mean and EF was good (r = 0.82, P less than 0.001). The selection of an AV-mean of less than 7 mm to define a severely depressed LV function (EF less than 30%) gave a sensitivity of 92% and a specificity of 67%. It is concluded that the AV plane displacement can be used to estimate LV systolic function in patients with CHF.

Cardiomyopathy, Dilated↗
PubMed1990

Characterization of Halobacterium halobium mutants defective in taxis.

Mutant derivatives of Halobacterium halobium previously isolated by using a procedure that selected for defective phototactic response to white light were examined for an array of phenotypic characteristics related to phototaxis and chemotaxis. The properties tested were unstimulated swimming behavior, behaviorial responses to temporal gradients of light and spatial gradients of chemoattractants, content of photoreceptor pigments, methylation of methyl-accepting taxis proteins, and transient increases in rate of release of volatile methyl groups induced by tactic stimulation. Several distinct phenotypes were identified, corresponding to a mutant missing photoreceptors, a mutant defective in the methyltransferase, a mutant altered in control of the methylesterase, and mutants apparently defective in intracellular signaling. All except the photoreceptor mutant were defective in both chemotaxis and phototaxis.

Bacterial Proteins↗
PubMed1990

HIV-1 neutralizing antibodies in urine from seropositive individuals.

HIV-1 neutralizing activity was demonstrated in serum and 200-fold concentrated urine from individuals who were HIV-1 antibody positive in both their serum and urine, including AIDS-KS, AIDS-OI, ARC, and asymptomatic patients. Virus neutralization activity was detected in 23 of 56 (41.1%) of the serum samples and in 19 of 56 (33.9%) of the urine samples tested, with titers ranging from 1:8 to 1:256 and 1:1 to 1:4, respectively. The highest frequency of HIV-1 neutralizing activity (87.5%) and the highest mean neutralization titers (1:65) were found in the ARC patients. A high prevalence of p24 antigen in serum and low numbers of T4-lymphocytes correlated with a low frequency of neutralizing activity in either serum or urine in the infected individuals. HIV-1 neutralizing activity in the urine was shown to be due to immunoglobulins using a Sephadex G-100 filtration gel. All 19 urine samples with neutralizing activity contained antibodies reactive with envelope glycoproteins gp160, gp120, and gp41 by Western blot, similar to that seen with serum. The frequency of HIV-1 neutralizing activity in the urine concentrates was generally associated with high titers of neutralizing antibody in the corresponding serum. These findings suggest that HIV-1 neutralizing antibodies are lost in the urine by an as yet unknown mechanism.

AIDS-Related Complex↗
PubMed1990

Practical value of echo Doppler evaluation of aortic and mitral stenosis: a comparative study with cardiac catheterization.

This retrospective analysis compares data derived by echocardiography and cardiac catheterization in the evaluation of aortic and mitral valve stenosis. Sixty-seven patients, aged 69 +/- 12 years, underwent 76 catheterization procedures. In all studies the Doppler recording was technically adequate. In 64 studies of patients with aortic stenosis, correlation was good between the gradient obtained at catheterization (peak 51 +/- 28 mm Hg, mean 48 +/- 24 mm Hg) and the Doppler gradient (peak 73 +/- 29 mm Hg, mean 41 +/- 17 mm Hg) (R = 0.78 peak, 0.77 mean). In 15 studies the aortic valve area, 0.8 +/- 0.2 cm2, calculated by the simplified continuity equation, correlated well with the catheterization valve area, 0.7 +/- 0.3 cm2, calculated by the Gorlin equation (R = 0.80). In 14 studies in mitral stenosis patients, the mean gradient at catheterization was 11 +/- 5 mm Hg compared to the Doppler gradient of 8 +/- 4 mm Hg (R = 0.58). The mitral valve area was 1.1 +/- 0.3 cm2 by the Gorlin equation and 1.2 +/- 0.3 cm2 by echo Doppler, using pressure half-time. When cardiac rhythm, the presence and severity of regurgitation, and the cardiac index were analyzed, none was shown to have demonstrable influence on the accuracy of the Doppler study. Doppler echocardiography can be used reliably to assess valvular stenosis in a clinical, noninvasive laboratory where routine tests are performed and interpreted by more than one individual.

Aged↗
PubMed1990

Biopharmaceutical studies of 3-substituted isatin derivatives.

The metabolic fate of isatin hydrazone (Ia), isatin-3-thiosemicarbazone (Ib), isatin-3-semicarbazone (Ic), isatin-3-phenylhydrazone (Id), isatin oxime (Ie) and 3-hydroxy-3-acetonyl oxindole (II) was studied in rabbits. The compounds were administered orally in the dose of 300 mg/kg body wt. Isatin anthranilic acid, tryptophan and nicotinic acid were identified as the major metabolites excreted in urine. The 3-hydroxy-3-acetonyl oxindole (II) gave on additional metabolite, oxindole. The major metabolites were separated and identified unambiguously on thin layer silica gel plate. Metabolic pathways have been proposed to explain the biotransformation of the compounds investigated.

Animals↗
PubMed1989

Quantitation of human immunodeficiency virus type 1 in the blood of infected persons.

We used end-point-dilution cultures to measure the level of infectious human immunodeficiency virus type 1 (HIV-1) in peripheral-blood mononuclear cells (PBMC) and plasma of 54 infected patients who were not receiving antiviral chemotherapy. HIV-1 was recovered from the plasma and PBMC of every seropositive patient, but from none of 22 seronegative control subjects. The mean titers in plasma were 30, 3500, and 3200 tissue-culture-infective doses (TCID) per milliliter for patients with asymptomatic infection, the acquired immunodeficiency syndrome (AIDS), and the AIDS-related complex, respectively. In PBMC, the mean titers were significantly higher for symptomatic patients (AIDS, 2200, and AIDS-related complex, 2700 TCID per 10(6) PBMC) than asymptomatic patients (20 TCID per 10(6) PBMC). The values for the symptomatic patients were considered to indicate that at least 1 in 400 circulating mononuclear cells harbored HIV-1. The HIV-1 titers of seven patients with AIDS or AIDS-related complex treated with zidovudine for four weeks decreased significantly in plasma but not in PBMC. In addition, the mean titer in the plasma of 20 patients receiving long-term zidovudine treatment (130 TCID per milliliter) was 25-fold lower than the mean for comparable untreated patients with AIDS or AIDS-related complex. We conclude that the levels of HIV-1 in plasma and PBMC are much higher than previous estimates. This high degree of HIV-1 viremia raises the possibility that the direct cytopathic effect of this retrovirus alone may be sufficient to explain much of the pathogenesis of AIDS.

AIDS-Related Complex↗