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Biomedical subjects

A G Williams

Publications and source records attributed to A G Williams.

At least 73 records · Page 4Linked to original sources
PubMed1989

Postprandial variations in the activity of polysaccharide-degrading enzymes in microbial populations from the digesta solids and liquor fractions of rumen contents.

The diurnal variations in the specific activities of polysaccharide-degrading enzymes after feeding were monitored in adherent and non-adherent microbial populations separated from bovine rumen liquor and digesta solids. There were marked differences in the activity profiles of the enzymes within the subpopulations. Enzymes involved in the degradation of soluble carbohydrates were more active in the non-adherent populations, and in the liquor phase subpopulation activities increased in the 1-2 h post-feed period. The muralytic enzymes were most active in the adherent population. Specific activities increased by up to 20-fold over the 24 h period, with an initial five-fold increase occurring between 8 h and 12 h after feeding. Enzyme levels in the three non-adherent populations were similar at the end of the postprandial period. In the population recovered from the liquid associated with the digesta particles, however, the activities did not increase until the latter stages of the period, whereas in the non-adherent population from the digesta solids the activities varied little during the diurnal cycle. The numbers of micro-organisms associated with the digesta solids were similar at 2 h and 20 h after feeding; the variations in enzyme levels did not occur as a result of a population increase but were due to increased activities in an established population. The plant cell wall structural polysaccharides were degraded at different rates. There was no appreciable cellulose digestion during the first 8 h of the postprandial period and although hemicellulosic constituents were removed continuously the rate of loss of both polymers was increased in the later stages of the diurnal cycle when enzyme activities were maximal.

Animal Feed↗
PubMed1989

Does peripheral collateralization also cause collateralization in the canine heart?

1. Experiments were conducted in chronically prepared dogs to determine if gradual obstruction of the proximal femoral arteries would also cause collateralization in the coronary circulation. 2. Peripheral coronary pressure was measured before and after peripheral collateralization as an index of coronary collateral function. Coronary collateral blood flow was measured with radioactive microspheres after peripheral collateralization. 3. Peripheral coronary pressure was not significantly altered by peripheral collateralization. Coronary collateral blood flow measured after peripheral collateralization was similar to that reported in non-collateralized hearts. 4. Results indicated that the mechanism(s) responsible for peripheral collateralization do not act systemically, at least not on the coronary circulation.

Animals↗
PubMed1989

Oxygen consumption by ruminal microorganisms: protozoal and bacterial contributions.

The relative contributions to O2 consumption made by the protozoal and bacterial populations present within the rumen were determined by using an open-type oxygen electrode system. Measurements indicated that two separate microbial populations contributed approximately equally to ruminal O2 consumption over the O2 concentration range experienced in situ (0.25 to 1.0 microM). The populations were observed to consume O2 under liquid-phase O2 concentrations of up to 7 microM, above which point rapid inactivation of O2 utilization was observed. Km values for the mixed population of bacteria and protozoa were 0.36 +/- 0.17 and 3.2 +/- 0.4 microM at concentrations of less than 1.6 and greater than 1.6 microM, respectively. O2 affinity values obtained for both the protozoal and bacterial populations were similar. O2 affinities of the isolated entodiniomorphid ciliates Polyplastron multivesiculatum and Eudiplodinium maggii showed O2 inhibition thresholds of 10 and 5, respectively, and apparent half-saturation constants (Km values) of 1.7 and 5.2 microM O2, respectively. Corresponding Vmax values were 7.8 microM O2 per min per 10(5) organisms for P. multivesiculatum and 3.6 microM O2 per min per 10(5) organisms for E. maggii. Mass spectroscopic analysis detected average rates of H2 production of 12.0 and 3.7 microM H2 per min per 10(5) organisms for P. multivesiculatum and E. maggii, respectively. Trace levels of dissolved O2 (less than 0.25 microM) stimulated the H2 production rate of E. maggii eightfold but inhibited that of P. multivesiculatum by 18%.

Animals↗
PubMed1989

Neurite penetration into collagen gels requires Ca2+-dependent metalloproteinase activity.

Cultured sympathetic neurons from neonatal rats release a Ca2+-dependent metalloproteinase capable of degrading native and denatured type I collagen. A large fraction of the metalloproteinase activity is released from growth cones of growing neurites, which suggests that this proteinase may be involved in neurite penetration into collagen-rich extracellular matrices during development. In the present study, we investigated the possibility that neurite penetration into 3-dimensional collagen gels requires the Ca2+-dependent metalloproteinase. Sympathetic neurons were plated on top of collagen gels and the neuronal metalloproteinase activity was inhibited with the collagenase inhibitor HSCH2CH[CH2CH(CH3)2]-CO-Phe-Ala-NH2 (HS-LFA). HS-LFA inhibited the Ca2+-dependent metalloproteinase activity, penetration of neurites into collagen gels and release of 3H from 3H-collagen gels in a dose-dependent manner over very similar concentration ranges (EC50 = 150-200 nM). Highly significant correlations existed between neurite penetration into collagen gels and metalloproteinase activity (r = 0.99), and metalloproteinase activity and release of 3H from 3H-collagen gels (r = 0.99). Although HS-LFA inhibited the growth of neurites within collagen gels, it had no effect on neurite outgrowth on collagen films. Thus, the neuronal Ca2+-dependent metalloproteinase appears to be required for neurite penetration into and growth within 3-dimensional collagen matrices, but not for growth along a 2-dimensional collagen substrate.

Animals↗
PubMed1989

Regression and recovery of well-developed coronary collateral function in canine hearts after aorta-coronary bypass.

After restoration of antegrade blood flow by coronary artery bypass grafting to a region of myocardium supplied by well-developed collateral vessels, there is regression of collateral supply to that region. There is controversy as to how rapidly this regression occurs, how soon collateral flow might return after an acute occlusion of the bypass graft, and how effective pharmacologic agents such as nitroglycerin might be in accelerating this return. To investigate this problem, 14 canine hearts were collateralized by Ameroid occlusion of the left anterior descending coronary artery. Regression and recovery of well-developed collateral function were studied after opening and closing an aorta-coronary bypass. Before bypass, peripheral coronary pressure was 82 +/- 2 mm Hg, retrograde flow 63 +/- 7 ml/min, collateral flow 21 +/- 2 ml/min, and collateral resistance 0.96 +/- 0.13 mm Hg/ml/min. One hundred minutes of bypass perfusion significantly decreased peripheral coronary pressure by 27%, retrograde flow by 52%, and collateral flow by 42%, and significantly increased collateral resistance by 319%. When the bypass was acutely occluded for 30 minutes, collateral resistance decreased spontaneously by 37%. When intracoronary nitroglycerin was administered for 5 minutes immediately after bypass occlusion, collateral resistance rapidly decreased by 72%, but subsequent collateral regression was not alleviated. Increased flow through regressed collateral vessels during retrograde flow diversion was associated with a decrease in collateral resistance. Results demonstrate rapid but not instantaneous regression and recovery of mature collateral function in response to requirements of collateral-dependent myocardium. Regressed collateral vessels can be dilated by nitroglycerin. Flow-dependent changes in collateral vascular tone appear to be responsible for early regression and recovery of collateral function.

Animals↗
PubMed1988

Synergism of rumen microbial hydrolases during degradation of plant polymers.

In isolated mixture of exocellular enzymes of rumen bacteria Ruminococcus flavefaciens, Butyrivibrio fibrisolvens and rumen fungus Neocallimastix frontalis, specific activities of cellulases, hemicellulases and glycosidases were determined. The highest specific activities were shown mostly for proteins of N. frontalis.

Animals↗
PubMed1988

Dominant role of circulating catecholamines in the myocardial contractile response to intravenous nicotine.

Experiments were conducted in anesthetized dogs to determine the mechanism primarily responsible for the increase in myocardial contractile function during intravenous infusion of nicotine. Myocardial function was assessed regionally by measuring segment shortening using ultrasonic dimension gauges. The role of cardiac neural stimulation in the absence of direct effects of nicotine and other circulating factors was evaluated by perfusing a region of left ventricular myocardium with blood from a reservoir during systemic nicotine infusion. Segment shortening increased from 11 to 19% in normally perfused myocardium but deteriorated to nearly 0% in reservoir-perfused myocardium. To evaluate direct effects of nicotine on cardiac function, nicotine was infused directly into a perfused coronary artery. An intracoronary concentration of nicotine equivalent to that caused by intravenous administration (0.69 +/- 0.08 micrograms/ml plasma) had no effect on myocardial contractile function. An intracoronary nicotine concentration of 5 micrograms/ml was required to directly increase contractile function to approximately the same extent observed during intravenous nicotine. To evaluate the role of circulating catecholamines in the myocardial response to intravenous nicotine, observations were made before and after bilateral adrenalectomy. Adrenalectomy markedly attenuated the pressor response to intravenous nicotine and abolished the positive cardiac inotropic response. We conclude that the adrenal release of catecholamines is primarily responsible for increased myocardial contractile function during intravenous nicotine.

Adrenalectomy↗
PubMed1988

Proteinase activity in rumen ciliate protozoa.

Azocasein-degrading proteinase activity was detected in all rumen ciliate protozoa that were examined from four entodiniomorphid and two holotrich genera. All of the activities were optimal in the range pH 4.0-5.0 and were inhibited by cysteine proteinase inhibitors, notably leupeptin. The inhibition profiles and extent of inhibition observed with the different groups of inhibitors were organism-specific. Gelatin-SDS-polyacrylamide gel electrophoresis of protozoal lysates revealed multiple forms of the proteinases in the species examined. The number of enzymes detected, their molecular masses, the level of activity and inhibitor susceptibility was genus-dependent. The proteinase profiles of the two holotrich species differed and inter-species differences were also apparent among species of the genus Entodinium. The characteristics and molecular size distribution of rumen bacterial proteinases were different to the protozoal proteinases. Low levels of proteinase activity, of apparently bacterial origin, were detected by gelatin-SDS-PAGE analysis of cell-free rumen liquor.

Animals↗
PubMed1988

Peripheral embolization provides evidence for microvascular collaterals in hearts with chronic coronary artery occlusion.

Macroscopic collateral vessels are widely regarded as the primary source of blood flow to collateral-dependent myocardium. Microscopic coronary collateral vessels have also been described, but their functional significance is controversial. Experiments were conducted in 18 anesthetized dogs with chronic coronary artery occlusions. Indices of collateral function demonstrated that all hearts were well-collateralized. The previously occluded coronary artery was cannulated distal to the obstruction for measuring retrograde flow before and after injection of either 13 microns or 84 microns emboli. Mean arterial pressure and heart rate were not altered by coronary embolization. Embolization with 13 micron spheres caused retrograde flow to increase by 43% (n = 11), whereas embolization with 84 micron spheres had no effect on retrograde flow (n = 7). Retrograde flow dislodged occlusive 84 micron spheres, since these spheres were found in the retrograde flow, and since antegrade flow increased by 250% after retrograde flow diversion. These findings demonstrate that collateral vessels less than 84 micron diameter contribute significantly to perfusion of chronically collateral-dependent myocardium.

Animals↗
PubMed1987

Polysaccharide-degrading enzymes formed by three species of anaerobic rumen fungi grown on a range of carbohydrate substrates.

The range of polysaccharide-degrading enzymes formed by three anaerobic rumen fungi (Neocallimastix patriciarum, Piromonas communis, and an unidentified isolate (F] was monitored following growth on seven mono-, di-, and poly-saccharide carbohydrate substrates. Enzymes capable of degrading a variety of alpha- and beta-glucans, beta-galactans, galactomannan, and hemicellulosic arabinoxylans were present in all three isolates. Although reducing saccharides were released from pectin, polygalacturonic acid was not degraded by the preparations. Enzyme activity was present in both the zoospore and vegetative stages of the life cycle and was also detected extracellularly in culture supernatants after vegetative growth. The specific activities of the polysaccharidases were affected by the growth substrate, being lowest in preparations grown on mono- and di-saccharides, whereas polysaccharidic growth substrates resulted in increased activity of the corresponding polysaccharidases. The enzymes were, however, formed after growth on all substrates. Oligomers and monosaccharides were produced as a result of polysaccharide breakdown by the unfractionated enzyme preparations. Studies on hemicellulose (arabinoxylan) breakdown by unfractionated vegetative preparations of the three isolates indicated that their modes of action, pH optima, substrate affinities, and response to potential inhibitors were similar.

Animals↗
PubMed1987

Glycoside hydrolase enzymes present in the zoospore and vegetative growth stages of the rumen fungi Neocallimastix patriciarum, Piromonas communis, and an unidentified isolate, grown on a range of carbohydrates.

The rumen fungi Neocallimastix patriciarum, Piromonas communis, and a morphologically distinct but unidentified isolate were cultivated on the polysaccharides starch, cellulose, xylan, and their principal component monosaccharides and disaccharides, and the range and specific activities of the glycoside hydrolases formed were monitored using gluco-oligosaccharide and p-nitrophenyl glycoside substrates. A wide range of enzyme activities was detected in preparations from vegetative growth and zoospores of all three isolates. Enzyme activity was also present in the culture medium. The specific activities were affected by the carbohydrate source available in the growth medium, although the more active hydrolases involved in the degradation of plant structural and storage polysaccharides were formed on all seven carbohydrate sources evaluated. Enzyme activities were increased in the zoospore, vegetative, and extracellular preparations after growth on the appropriate structurally related disaccharide or polysaccharide. The hemicellulolytic glycosidases (alpha-L-arabinofuranosidase, beta-D-xylosidase) were most active after growth on xylan, whereas alpha-/beta-glucosidase activity was increased with the corresponding glucan as growth substrate. However, whereas wide-ranging beta-glucosidase activity was detected following growth on maltose or starch, the alpha-glucosidase activities of P. communis were lower or undetectable in vegetative preparations grown on glucose or the beta-glucans cellobiose and cellulose.

Animals↗
PubMed1986

Fat embolism syndrome.

The fat embolism syndrome is clinically evident in approximately 0.5-2.0% of patients with long bone fractures. The clinical signs and symptoms are evident in 60% of patients within 24 hours and 85% of patients within 48 hours after trauma. A patient is reported who complained of dyspnea and hemoptysis approximately 72 hours after sustaining a fracture to the distal tibia and fibula. Radionuclide ventilation/perfusion imaging was obtained to rule out pulmonary thromboemboli. Perfusion imaging demonstrated the characteristic diffuse, subsegmental ("mottled") appearance of fatty emboli to the lung.

Adult↗
PubMed1986

Population characteristics and absorbed dose to the population from nuclear medicine: United States--1982.

Those in the U.S. population who receive nuclear medicine examinations have been characterized by age and sex. Males received 42% of examinations while females received 58%. More than one-third of the examinations were done on persons older than 64 y of age and more than two-thirds on patients older than 45 y of age. The per caput effective dose equivalent from nuclear medicine procedures in 1982 was 140 muSv (14 mrem); whereas, the per caput age-specific effective dose equivalent to the U.S. population was 50 muSv (5.9 mrem). These can be compared with 2 mSv (200 mrem) from natural background.

Adolescent↗
PubMed1986

Chest radiographs obtained with shaped filters: evaluation by observer performance tests.

The effectiveness of a shaped filter in improving nodule and infiltrate detection was measured by observer performance testing. Seven observers read 152 test radiographs of the chest obtained from human volunteers. Half the test radiographs had target images. Observer performance in detecting nodule or infiltrate images was compared with the shaped-filter system and with a conventional chest imaging system. The results were analyzed using receiver operating characteristic (ROC) techniques and indicate that the filter technique was not significantly different from the conventional technique in infiltrate depiction. Observer performance in detecting nodules was slightly worse on images obtained with the shaped-filter system.

Filtration↗