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Biomedical subjects

J L Samuel

Publications and source records attributed to J L Samuel.

At least 109 records · Page 6Linked to original sources
PubMed1985

Microtubules and desmin filaments during the onset of heart growth in the rat.

Microtubules and intermediate desmin filaments were visualized in rat cardiomyocytes during the onset of heart growth by double immunolabelling of isolated myocytes, with specific antibodies raised against tubulin and desmin. Heart growth was stimulated either by mechanical overloading induced by aortic stenosis, or by injection of thyroxine into hypothyroid rats. In both experimental models, alterations in the microtubule pattern were observed soon after stimulation of growth whereas desmin filament organization remained unchanged. Microtubules were redistributed in arrays parallel to the long axis of the myocytes and were more numerous around the nuclei. Microtubules therefore appeared to be involved in the cellular events occurring during stimulated heart growth irrespective of the nature of the stimulus.

Animals↗
PubMed1985

Myofibrillar organization and desmin in rat heart myocytes.

The distribution of desmin, and alpha-actinin was studied in vivo growing rat heart myocytes and in vitro cultured heart myocytes using double indirect immunofluorescence labelling. Myocytes growing in vivo exhibited a superimposable pattern of alpha-actinin and desmin at the level of the Z discs and intercalated discs. Cultured neonate rat heart myocytes concurrently exhibited changes in shape and a loss of myofibrillar register. Whereas alpha-actinin staining remained unchanged, that of desmin disappeared from the Z discs but persisted as cables and randomly oriented foci throughout the sarcoplasm. We conclude that desmin binding to the Z discs is correlated with the in register organization of myofibrils.

Actinin↗
PubMed1984

Unchanged myosin kinase activity in hypertrophied rat heart.

The decrease in myosin ATPase activity observed in cardiac hypertrophy induced by cardiac overload has been related to an isoenzymic redistribution of myosin. To test the hypothesis of an additional regulation of myosin ATPase through light chain phosphorylation, we measured the myosin kinase activity together in sham-operated and 50% to 100% hypertrophied rat hearts. The myosin kinase were purified approximately 600 fold with 6% yield by ion exchange chromatography and calmodulin-affinity chromatography. The presence of very important levels of proteolytic activity in the rat heart resulted in a partial loss of the myosin kinase calmodulin-dependency. The major component from both myosin kinase purified fractions was a 63 kdaltons protein. The protein content was identical in myosin kinase purified fractions from sham-operated and hypertrophied hearts. The calmodulin-dependent activity of myosin kinase, assayed in the presence of 0.1 mM Ca2+ and 10(-6) M calmodulin (about 6.6 nmol P X min-1 X mg-1), was identical in sham-operated and 50% to 100% hypertrophied hearts. Thus, myosin kinase specific activity, in these conditions, was unchanged in rat heart chronic hypertrophy. This result suggests that no direct functional relationship exists between the enzymatic properties of myosin and myosin kinase during the chronic phase of cardiac hypertrophy.

Adenosine Triphosphatases↗
PubMed1984

Isomyosins, microtubules and desmin during the onset of cardiac hypertrophy in the rat.

Chronic overloading of the rat heart induces a cascade of adaptational events which compensate for the increase in work. Two of these have been extensively described: a qualitative event with an isomyosin change leading to an improved efficiency and a quantitative event resulting in cardiac hypertrophy. By means of immunofluorescence, we investigated if elements of the cytoskeleton, i.e. microtubules and intermediate filaments, could be triggers for these adaptational mechanisms. Studies of overloaded heart were performed in young rats with aortic stenosis or adult rats with aortic insufficiency. Cardiac myocytes were isolated and labelled by immunofluorescence with antibodies raised against V1 or V3 isomyosin, desmin or tubulin. The aim of the work was to visualize: when and where the shift in the expression of isomyosins occurs within the myocytes; the eventual changes in the pattern of intermediate filaments of desmin and/or of microtubules during the adaptation of myocytes to overload. We observed: that the shift from the high (V1) to low (V3) ATPase isomyosin occurred in a population of myocytes soon after stenosis; that changes in the pattern of microtubules occurred soon after induction of hypertrophy; no changes in the distribution or intensity of the staining of desmin.

Adenosine Triphosphatases↗
PubMed1984

Different distributions of microtubules, desmin filaments and isomyosins during the onset of cardiac hypertrophy in the rat.

To elucidate the role of the cytoskeleton in the development of adult heart, microtubules and intermediate filaments of desmin were studied in young and adult rat heart myocytes during the onset of growth, after mechanical overloading induced by aortic stenosis. Such overloading is known to cause heart hypertrophy by stimulating overall protein synthesis, and to initiate a shift in myosin isozymes. For this study, we used double immunolabelling of isolated myocytes with specific antibodies raised against tubulin, desmin, and the two main isomyosins V1 and V3. Whereas desmin remained unchanged, tubulin was redistributed in arrays parallel to the long axis of the myocytes, and was densest around the nuclei. Alterations in the microtubule pattern were observed very early after aortic stenosis, during the onset of heart growth; they were transitory, and did not occur simultaneously in all myocytes. Chronological examination of myocytes labelling with both antitubulin and anti V3 myosin clearly suggested that the transitory alteration in the microtubule pattern was an early event preceding the change in the expression of the myosin gene. Results, observed in young rats, in which mitosis is stimulated by overloading, and in adult rats, exhibiting no mitosis, showed that microtubules are involved in the development of cells in which mitosis does not occur. This work provides the first evidence of a correlation in functional adult heart, between the reorganization of cytoplasmic microtubules and the onset of growth.

Animals↗
PubMed1983

Circadian changes in heart rate in unanesthetized normotensive and spontaneously hypertensive rats.

Circadian changes in heart rate and heart rate variability were measured in spontaneously hypertensive (SHR) and normotensive (WKY) rats. Electrocardiograms (ECG) were continuously recorded, over a 24 hour period from freely moving conscious rats via three small metallic subcutaneous electrodes which were positioned a week before the recording period. The findings reported here show: 1/ Mean heart rate calculated over 24 hours were lower in both strains than previously reported. This difference probably reflects the lack of anesthesia and minimal stress in the present study. 2/ The timing of the circadian variations in both strains were the same, suggesting that were both entrained to the light-dark cycle. 3/ The 24 hours mean heart rate variability was significantly higher in SHR than in WKY but in each strain it was similar throughout the 24 hours. This suggests that the vagal tone in SHR was higher by a fairly constant amount throughout the light-dark cycle.

Animals↗
PubMed1983

Jaw disease in macropod marsupials: bacterial flora isolated from lesions and from the mouths of affected animals.

Bacterial infections of the jaws are a common cause of death in macropods. Lesions and oral cavities from 50 affected animals yielded wide ranges of aerobic and anaerobic organisms. The most frequent isolate from lesions (81%) was Fusobacterium necrophorum, generally combined with other bacteria, but in 5 lesions, in pure culture. It was also isolated from 61% of mouths and this was the chief difference between the oral flora of affected and normal macropods. Other groups of organisms isolated from over 50% of lesions were: Gram-negative aerobic and anaerobic rods, streptococci, anaerobic Gram-positive cocci. Actinomycetes were isolated from 29% of lesions and from one lesion in pure culture. Differences in the flora were detected between lesions in bone and soft tissue and between closed and open lesions. Antibiotics were given to 22 animals, but without significant differences in frequencies of isolation of organisms between treated and untreated groups, and with no permanent elimination of infection. It was concluded that, while different organisms might be present in the complex of "jaw disease", the pathogenic agent in the majority of cases was F. necrophorum. Actinomycetes were capable of producing lesions in bone, but their role in "jaw disease" remains undefined.

Actinomycetales↗
PubMed1983

Factors affecting the survival of Salmonella and Escherichia coli in anaerobically fermented pig waste.

The survival of Salmonella typhimurium was investigated in acidogenic, anaerobically fermented pig wastes and in synthetic media, each containing volatile fatty acids (VFA). Salm. typhimurium survived at pH 6.8, but not at pH 4.0, when incubated at 37 degrees C for 24 h in either fermented or synthetic medium containing VFA. The minimum inhibiting concentration of VFA for Salm. typhimurium after 48 h incubation at 30 degrees C at pH 4.0 was 0.03 mol/l and for Escherichia coli it was 0.09 mol/l. Fermented pig wastes in a digester, maintained at pH 5.9, were inoculated with Salm. typhimurium and then incubated at 37 degrees C for 24 h. The pH was adjusted to either 4.0 or 5.0 and after a further 48 h at 30 degrees C, Salm. typhimurium survived at pH 5.0 but not at pH 4.0. It was concluded that pH is critical in determining the survival of this organism in acidogenic anaerobically fermented pig waste.

Animals↗
PubMed1983

Distribution of myosin isozymes within single cardiac cells. An immunohistochemical study.

Isozymes of myosin have been localized with respect to individual cardiac myocytes in hearts from 3-week-old, adult controls, and adult hypophysectomized rats, and in cultured cardiac cells. For this purpose, affinity-purified antibodies reacting specifically with the heavy chains of each of the two major myosin isozymes of adult rat heart, V1 and V3, were used. The distribution of the two isomyosins was determined by double immuno-labeling of the same cell, V1 myosins being revealed by rhodamine and V3 myosins by fluorescein. A procedure is described which allows optimum immunological visualization of the myosin filaments of rod-shaped isolated myocytes. It was found that the response of the cardiac cells to the two antimyosins varied depending on the state of the animal. In 3-week-old rats, all cells were stained with the anti-V1, and almost none with the anti-V3 myosin. In the hypophysectomized animals, on the contrary, all cells were stained with the anti-V3 and none with the anti-V1. A mixed pattern of reactivity was observed in adult controls since 50% of the cells reacted with the anti-V1, 10% with the anti-V3, and 40% with both antibodies. In the latter case, the distributions of V1 and V3 reactivities were homogeneous throughout the cell, and absolutely superimposable. The same double reactivity and homogeneous repartition were observed in cultured cells. These findings indicate that myocytes from adult rat myocardium are heterogeneous in terms of their isomyosins content and show for the first time that two isomyosins can coexist and be equally distributed in one cardiac cell. These observations are relevant to the regulation of individual heart cell contractility.

Animals↗
PubMed1983

Immunological quantitation and localization of tubulin in adult rat heart isolated myocytes.

Isolated myocytes were purified from adult rat heart. Identification and localization of microtubules and quantitation of tubulin in these cells were performed by immunochemical procedures. Antibodies were raised against brain tubulin and purified by affinity chromatography. An enzyme-linked immunosorbent assay, ELISA, was developed for quantitation of tubulin. It allowed the measurement of 10 to 500 ng of tubulin. Tubulin content in adult rat cardiac myocytes was found to be approximately 10 micrograms per 100 mg of the total protein content. By means of a double immunofluorescence technique, the microtubule network, identified with antitubulin, was studied in reference to the sarcomeric A band labeled with antibodies specific to myosin heavy chains. The basis for identifying the microtubule network have included the use of specific antitubulin immunoglobulins and the sensitivity of the specific labeling of the network to antimitotic drugs and low temperature. It was found that microtubules were organized mainly around the nuclei, with important concentrations at the poles, showing extensions in the cone and in the cytoplasm as loosely organized loops. The shape of adult cardiac myocyte was not dependent upon the integrity of the microtubule network.

Alkaloids↗
PubMed1982

The normal flora of the mouths of macropods (Marsupialia: macropodidae).

From swabs obtained from the mouths of 59 captive macropods and cultured for aerobic and anaerobic bacteria and fungi, the most frequent isolates were streptococci and aerobic Gram-negative rods. Other isolates, in order of diminishing frequency, were Gram-positive non-sporulating rods and filaments, staphylococci/micrococci, aerobic Gram-negative cocci, fungi, anaerobic Gram-positive cocci, anaerobic Gram-negative rods and filaments, species of Bacillus and Clostridium, and membranes of the Simonsiellaceae. No anaerobic Gram-negative cocci were isolated, and spirochaetes were seen only in one animal with periodontal pockets. Smears of material from the mouths of 5 wild wallabies showed organisms resembling those found in the captive animals.

Animals↗
PubMed1981

Salmonella in the intestinal tract and associated lymph nodes of sheep and cattle.

The distribution of salmonellas along the gastrointestinal tract and in associated lymph nodes were studied in 100 sheep and 100 cattle at slaughter. Animals were chosen from those slaughtered on the first day of the week, since this meant that they were likely to have been held at the abattoir for several days and thus to be at high risk of salmonella infection. The contents of the rumen, abomasum, ileum, caecum and rectum were sampled, together with the lymph nodes draining each of these sites. Of the cattle, 77 were carrying salmonellas, including 61 with infected lymph nodes, whereas only 43 sheep were infected, 14 of them with infections in the nodes. The lower prevalence in sheep than in cattle might be explained by a shorter time between leaving the property and slaughter. In both species, within the gastrointestinal tract salmonellas were most frequently found in the caecum and rectum and least frequently in the abomasum. In cattle salmonellas were frequently present, usually in large numbers, in the lymph nodes draining the ileum, caecum and colon, but rarely in the ruminal and abomasal nodes; however this difference was not apparent in sheep. Over 70% of infected animals yielded more than one serotype, the maximum number isolated from any one animal being ten.

Animals↗
PubMed1981

Myosin isoenzyme changes in several models of rat cardiac hypertrophy.

We studied the effect of chronic mechanical overloading on the isoenzyme composition of rat cardiac myosin in several experimental models: aortic stenosis (AS), aortic incompetence (AI), aortocaval fistula (ACF), overload of the non-infarcted area after left coronary ligation (INF), and overload of the spontaneously hypertensive rats (SHR). Samples of the left and right ventricles were isolated from these hearts, and myosins were analyzed by electrophoresis in non-dissociating conditions. The myosin isoenzymes were called V1, V2, and V3 in order of decreasing mobility, according to the nomenclature of Hoh et al. Controls of the Wistar and Wistar Kyoto (WKY) strains were almost exclusively V1, A slow age-dependent shift toward V3 was observed in the left ventricles of adult Wistar rats, which at 30 weeks of age (body weight 600 g) contained approximately 15% of this form. In all models of cardiac hypertrophy, an isoenzymic redistribution was observed with a significant increase in V3. The level of V3 was statistically correlated with the degree of hypertrophy in the AS, (n = 11, r - 0.6, P less than 0.05), the AI (n = 14, 4 = 0.88, P less than 0.001), and the AS + AI(n = 14, 4 = 0.69, P less than 0.01) but not in the ACF (n = 16, r = 0.46). The isoenzymic changes could account for the decreases in both myosin ATPase activity and cardiac contractility described previously in our laboratory and by others. They also demonstrate that changes in myosin isoenzymes represent a general response of the rat heart, to chronic mechanical overloading.

Animals↗
PubMed1980

The contamination with Salmonella of bovine livers in an abattoir.

Fifty livers from normal slaughter cattle were examined for surface contamination by Salmonella immediately after evisceration and again after inspection. Salmonella were isolated from 32% at evisceration and from 82% after inspection. Numbers of Salmonella present were low at evisceration, and rose after inspection. In only one liver was the parenchyma infected. The sources of the Salmonella were probably the contents of the gastrointestinal tract and the mesenteric lymph nodes, both of which may show high prevalence of infection in cattle which have been held before slaughter. It was concluded that edible offal should be separated from the viscera at evisceration and inspected by personnel who are not involved with the alimentary tract.

Abattoirs↗