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A G Williams

Publications and source records attributed to A G Williams.

At least 55 records · Page 3Linked to original sources
PubMed1994

Polypeptides of hydrogenosome-enriched fractions from rumen ciliate protozoa and trichomonads: immunological studies.

The evolution of hydrogenosomes, energy-generating organelles of rumen ciliate protozoa and the flagellate trichomonads has been the subject of much speculation. Polypeptides of the hydrogenosome-enriched fractions from the rumen ciliates, Dasytricha ruminantium, Isostricha spp., Polyplastron multivesiculatum and Eudiplodinium maggii were separated by SDS-PAGE and compared to analogous polypeptide preparations from Tritrichomonas foetus. Immunoblotting with antisera specific to the hydrogenosomes of T. foetus identified common immunoreactive polypeptides present at estimated molecular masses of 28, 35, 38, 44, 48, 58, 100 and 120 kDa. That at 120 kDa corresponds to a single subunit of the purified pyruvate:ferredoxin oxidoreductase from the hydrogenosome of Trichomonas vaginalis.

Animals↗
PubMed1994

Coronary pressure-flow autoregulation protects myocardium from pressure-induced changes in oxygen consumption.

Pressure-flow autoregulation minimizes changes in coronary blood flow (CBF) when coronary perfusion pressure (CPP) is altered. This investigation determined if autoregulation also minimizes CPP-induced changes in coronary vascular volume (CVV) and CVV-dependent changes in myocardial oxygen consumption (MVO2). In 11 anesthetized dogs, the left anterior descending coronary artery was cannulated, and responses to 20-mmHg changes in CPP were examined over a range of CPP from 60 to 180 mmHg. Changes in CPP had no significant effect on systemic hemodynamics or on left ventricular end-diastolic segment length, end-systolic segment length, or percent segment shortening. In hearts with effective pressure-flow autoregulation [closed-loop gain (GC) > 0.4], CVV increased 0.06%/mmHg change in CPP. For the same hearts, MVO2 increased 0.04%/mmHg change in CPP. In hearts with ineffective autoregulation (GC < 0.4), CVV increased 0.97%/mmHg (P < 0.001 vs. autoregulating hearts), and MVO2 increased 0.41%/mmHg (P < 0.001 vs. autoregulating hearts). MVO2 and CVV were correlated (r = 0.69, P < 0.0001) independently of autoregulatory capability, but only when autoregulation was poor and capacitance was elevated did CPP significantly affect MVO2. We conclude that pressure-flow autoregulation protects myocardium from CPP-induced changes in CVV, which in turn produces changes in oxygen consumption.

Analysis of Variance↗
PubMed1994

Isolation and characteristics of the protozoal and bacterial fractions from bovine ruminal contents.

Four cows were fed once a day either a Cocksfoot hay diet (H) or a diet consisting of 65% hay and 35% pelleted ground barley (HB). 15(NH4)2SO4 was continuously infused into the rumen as a microbial marker and ruminal digesta samples were collected during the 24-h postprandial period for the isolation of liquid-associated protozoa and bacteria (LAP, LAB) and particle-associated bacteria (PAB). There were marked differences between ruminal pH diurnal variations with diets H and HB. Irrespective of the diet and sampling time, the chemical composition (OM, N, DAPA, 15N) of the protozoa was clearly different from that of the bacteria (P < .001). The LAP contained more OM but less N and 15N than the bacterial fractions. The DAPA used to validate the isolation technique for the mixed ciliate population was not detected in protozoal fractions. The OM content of LAB was lower than that of PAB, whereas the N, DAPA, and 15N contents were higher. The observed effects of diet (P < .01) on LAP mean N contents were due to the different N contents of the LAP samples isolated 23 h after feeding and were correlated with the variation in the number of Endodiniomorphid protozoa (r = .72; P < .05). The N content of LAB was not affected (P > .05) by diet but that of the PAB was increased on diet HB (P < .05). The diet did not affect the 15N content of any of the three microbial populations. However, the 15N content of the bacteria decreased shortly after feeding (P < .001).

Animal Feed↗
PubMed1993

Effects of snuff on regional blood flow to the cheek and tongue of anesthetized dogs.

Regional blood flow to the cheek and tongue of anesthetized dogs was measured before and after application of six different doses of snuff (3.12 to 100 mg/kg body weight) to the right cheek. Dose-independent vasodilation was observed at the site of application, whereas dose-dependent vasoconstriction was observed contralaterally. Aortic, central venous, and ventricular pressures were significantly increased (p < 0.05) at the higher doses. Plasma nicotine concentrations increased stepwise with dose.

Analysis of Variance↗
PubMed1993

Arteriovenous-shunt-mediated increase in venous return causes apparent right coronary arterial autoregulation.

OBJECTIVE: Reports of autoregulation in the right coronary vasculature have varied from non-existent to almost perfect. At least some of this discrepancy may be due to failure to account for changes in myocardial metabolism secondary to the method used to vary perfusion pressure. The aim of this study was to determine if the potent autoregulation reported when right coronary perfusion pressure was lowered by opening a large arteriovenous shunt was due to increased right ventricular myocardial oxygen consumption (MVO2) induced by augmented preload and afterload. METHODS: Two protocols were used to produce right coronary perfusion pressures of 100, 80, and 60 mm Hg in anaesthetised dogs. In both protocols the right coronary artery was cannulated and supplied with blood from a pressurised chamber. In protocol 1, right coronary perfusion pressure was decreased independently of aortic pressure, and in protocol 2, aortic pressure was decreased in parallel with right coronary perfusion pressure by opening a large arteriovenous shunt. Right coronary blood flow, central venous pressure, and pulmonary arterial pressure were measured, and right ventricular oxygen extraction and MVO2. Central venous pressure (right ventricular preload) and pulmonary arterial pressure (right ventricular afterload) did not change. In protocol 2, opening the arteriovenous shunt increased venous return, as shown by increased central venous pressure and pulmonary arterial pressure. This increased right ventricular MVO2 at the lower right coronary perfusion pressures and maintained right coronary blood flow at the level recorded when right coronary perfusion pressure was 100 mm Hg. CONCLUSIONS: This apparently potent autoregulation resulted from the shunt induced increase in oxygen consumption at low right coronary perfusion pressures, in contrast to the decreased right ventricular oxygen consumption and right coronary blood flow observed when right coronary perfusion pressure is selectively decreased.

Animals↗
PubMed1993

Interstitial purine metabolites and lactate during regional myocardial hypoxia.

OBJECTIVE: Adenosine is a well known vasodilator believed to contribute to metabolic adjustments of the coronary circulation. The purpose of this study was to assess changes in interstitial fluid adenosine, adenosine metabolites, and lactate during prolonged regional, non-ischaemic myocardial hypoxia. METHODS: To induce regional hypoxia, the left anterior descending coronary artery of anaesthetised dogs (n = 9) was perfused at constant pressure (100 mm Hg) with deoxygenated blood (PO2 approximately 2.6 kPa) for 60 min via an extracorporeal shunt. Cardiac interstitial fluid was sampled by cardiac microdialysis, using dialysate metabolite levels as indices of interstitial fluid concentrations. RESULTS: During hypoxia, coronary blood flow increased 3.9-fold, while myocardial oxygen consumption was maintained relatively constant. There were no changes in global cardiac function, systemic arterial pressure, or heart rate during regional hypoxia, indicating that the hypoxic stimulus did not augment sympathetic nervous system activity. Dialysate adenosine was not increased at any point of the hypoxic period, but was decreased by 25 min hypoxia. Dialysate levels of inosine, hypoxanthine, and xanthine were increased transiently during the first 10 min of hypoxia while there was a sustained increase in dialysate lactate. In the presence of erythro-9-(2-hydroxy-3-nonyl) adenine, an adenosine deaminase inhibitor, adenosine was the predominant purine metabolite and increased transiently during hypoxia. CONCLUSIONS: Flux through the adenosine production and degradation pathways is transiently increased during hypoxia. However, the lack of an increase in interstitial fluid adenosine does not support a role for adenosine in the sustained hyperaemic response to regional myocardial hypoxia.

Adenosine↗
PubMed1993

Changes in the rumen microbial population and its activities during the refaunation period after the reintroduction of ciliate protozoa into the rumen of defaunated sheep.

Changes in the microbial populations, their activities, and the ruminal fermentation were monitored for 50 d following the reintroduction of ciliate protozoa into four defaunated sheep. A protozoal population was reestablished successfully in each recipient, using a washed inoculum containing approximately 10(3) cells, although there were between-animal differences in the rates of recolonization and genus establishment. Entodinium spp. predominated in the initial stages of the refaunation period and had an apparent maximal generation time of 9-10 h. Bacterial and fungal numbers did not decline following the reintroduction of protozoa and a small transient increase in the numbers of amylolytic and xylanolytic bacteria and fungal zoospores occurred in the early stages of refaunation when the protozoal population was < 10(5)/g ruminal contents, but these subsequently declined as the protozoa established. Although the fibrolytic bacterial population was lowest in period 3 (> 10(5) protozoa/g), the in sacco ruminal digestion of Lolium perenne hay and polysaccharolytic enzyme activities in the solids-associated populations were either maintained or increased when protozoa were present confirming the important contribution of protozoa to fibre breakdown in the rumen. Significant changes in ruminal microbial activities occurred after protozoal reinoculation but before the rumen had refaunated completely. Arylamidase activities in the liquor-phase population and ruminal ammonia concentrations increased significantly within 48 h of transfaunation; the magnitude of the effects became more pronounced as the protozoal population developed. However, volatile fatty acid formation and ruminal pH were not affected after the reintroduction of protozoa.

Aminopeptidases↗
PubMed1992

Canine coronary vasodepressor responses to hypoxia are attenuated but not abolished by 8-phenyltheophylline.

The purpose of this study was twofold: 1) to verify a report that a suspension of 8-phenyltheophylline (8-PT) completely abolished hypoxia-induced coronary vasodilation [H. M. Wei, Y. H. Kang, and G. F. Merrill. Am. J. Physiol. 257 (Heart Circ. Physiol. 26): H1043-H1048, 1989] and 2) to determine the effect of dissolved 8-PT on hypoxic hyperemia. The left anterior descending coronary artery of anesthetized dogs was cannulated and perfused at either constant flow or constant pressure. An 8-PT suspension (40 micrograms.kg-1.min-1) produced a twofold elevation of coronary perfusion pressure at constant flow, a 97% decrease in coronary flow at constant pressure, and regional akinesia in both conditions. The coronary vasculature was unresponsive to 60-s coronary occlusion, exogenous adenosine, and hypoxia after infusion of the 8-PT suspension. These findings are consistent with obstruction of the coronary microvasculature by the 8-PT suspension. An 8-PT solution (40 micrograms.kg-1.min-1) produced 95 +/- 3% (P less than 0.001, n = 6) attenuation of exogenous adenosine-induced vasodilation at constant pressure, a 28 +/- 5% (P less than 0.01, n = 6) attenuation of reactive hyperemia, and a 24 +/- 6% (P less than 0.05, n = 6) decrease in hypoxia-induced vasodilation. An 8-PT solution had no effect on systolic segment length shortening and myocardial oxygen consumption. We conclude that 8-PT, when in solution, attenuates but does not abolish the coronary vasodilatory response to hypoxia. Hence, adenosine appears to contribute to hypoxia-induced vasodilation but is not uniquely responsible for the hyperemic response.

Adenosine↗
PubMed1992

Effects of a coronary alpha 1-constriction on transmural left ventricular flow and contractile function.

Modulation of myocardial contractile function and perfusion by alpha 1-adrenergic receptors were examined in anesthetized dogs during left stellate ganglion stimulation. In 11 dogs, stellate stimulation significantly increased heart rate, mean arterial pressure, left ventricular systolic pressure, maximal rate of left ventricular pressure generation, segmental shortening and rate of shortening in anterior and posterior ventricular regions, and myocardial oxygen extraction. Myocardial lactate extraction decreased. The selective alpha 1-adrenergic antagonist prazosin (0.5 mg) injected into the circumflex artery during stellate stimulation caused significant additional increases in maximal rate of left ventricular pressure generation by 19 +/- 5% and in rate of shortening in posterior subendocardium by 20 +/- 6%. No changes were observed in posterior subepicardial or anterior subendocardial segmental contractile function. Myocardial oxygen and lactate extractions returned to their control values following prazosin injection. Regional left ventricular perfusion was measured using tracer microspheres in five additional dogs. Stellate stimulation increased subepicardial and subendocardial perfusion by 30%. Prazosin increased both subepicardial and subendocardial perfusion by an additional 36%. Stellate stimulation increased norepinephrine concentration in the coronary sinus, but no further increase was noted after blockage of alpha 1-receptors by prazosin. Thus, during sympathetic stimulation, an alpha 1-vasoconstriction existed uniformly across the left ventricular wall. However, blockade of this vasoconstriction was associated with an increase in contractile function only in the deeper muscle layers.

Adrenergic alpha-Antagonists↗
PubMed1991

Receptor and G protein-mediated responses to thrombin in HEL cells.

Thrombin is believed to activate platelets via cell surface receptors coupled to G proteins. In order to better understand this process, we have examined the interaction of thrombin with HEL cells, a leukemic cell line that has served as a useful model for studies of platelet structure and function. In HEL cells, as in platelets, thrombin stimulated inositol trisphosphate (IP3) formation and suppressed cAMP synthesis. Both events were inhibited by pertussis toxin with 50% inhibition occurring at a toxin concentration that ADP-ribosylated 50% of the Gi alpha subunits present in HEL cells. IP3 formation was also stimulated by a second serine protease, trypsin. The trypsin response was identical to the thrombin response in time course, magnitude, and pertussis toxin sensitivity, suggesting that a similar mechanism is involved. Agonist-induced changes in the cytosolic-free Ca2+ concentration were used to test this hypothesis. Both proteases caused a transient increase in intracellular calcium [Ca2+]i that could be inhibited with D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone thrombin. Exposure to either protease desensitized HEL cells against subsequent increases in [Ca2+]i and IP3 caused by the other, although responses to other agonists were retained. This loss of responsiveness persisted despite repeated washing of the cells and the addition of hirudin. Complete recovery occurred after 20 h and could be prevented with cycloheximide. These observations suggest that 1) HEL cell thrombin receptors, like those on platelets, are coupled to phospholipase C and adenylylcyclase by pertussis toxin-sensitive G proteins, 2) the G proteins involved are equally accessible to pertussis toxin in situ, 3) when access is limited to the outside of the cell the response mechanisms for thrombin and trypsin are similar, if not identical, despite the broader substrate specificity of trypsin, 4) both proteases cause persistent changes that may involve proteolysis of their receptors or associated proteins, and 5) desensitization of the thrombin response occurs at a step no later than the activation of phospholipase C and requires protein synthesis for recovery.

Adenosine Diphosphate Ribose↗
PubMed1991

Influence of CO2 and low concentrations of O2 on fermentative metabolism of the rumen ciliate Dasytricha ruminantium.

The effects of ruminal concentrations of CO2 and O2 on glucose-stimulated and endogenous fermentation of the rumen isotrichid ciliate Dasytricha ruminantium were investigated. Principal metabolic products were lactic, butyric and acetic acids, H2 and CO2. Traces of propionic acid were also detected; formic acid present in the incubation supernatants was found to be a fermentation product of the bacteria closely associated with this rumen ciliate. 13C NMR spectroscopy revealed alanine as a minor product of glucose fermentation by D. ruminantium. Glucose uptake and metabolite formation rates were influenced by the headspace gas composition during the protozoal incubations. The uptake of exogenously supplied D-glucose was most rapid in the presence of O2 concentrations typical of those detected in situ (i.e. 1-3 microM). A typical ruminal gas composition (high CO2, low O2) led to increased butyrate and acetate formation compared to results obtained using O2-free N2. At a partial pressure of 66 kPa CO2 in N2, increased cytosolic flux to butyrate was observed. At low O2 concentrations (1-3 microM dissolved in the protozoal suspension) in the absence of CO2, increased acetate and CO2 formation were observed and D. ruminantium utilized lactate in the absence of extracellular glucose. The presence of both O2 and CO2 in the incubation headspaces resulted in partial inhibition of H2 production by D. ruminantium. Results suggest that at the O2 and CO2 concentrations that prevail in situ, the contribution made by D. ruminantium to the formation of ruminal volatile fatty acids is greater than previously reported, as earlier measurements were made under anaerobic conditions.

Animals↗
PubMed1991

Effect of ciliate protozoa on the activity of polysaccharide-degrading enzymes and fibre breakdown in the rumen ecosystem.

The effect of ciliate protozoa on the activity of polysaccharide-degrading enzymes in microbial populations from the digesta solids and liquor fractions of rumen contents was examined after the refaunation of ciliate-free sheep with an A-type rumen protozoal population. Although the culturable rumen bacterial population was reduced after refaunation the number of fibrolytic micro-organisms detected was higher; the xylanolytic bacterial population and numbers of fungal zoospores were increased after refaunation. The proportion of propionic acid was lower in the refaunated animals, whereas the concentration of ammonia and the acidic metabolites acetate, butyrate and valerate were all increased. The range of enzyme activities present in the digesta subpopulations were the same in defaunated and refaunated animals. The activities of the polysaccharide-degrading enzymes, however, were increased in the microbial populations associated with the digesta solids after refaunation, and at 16 h after feeding the activities were 4-8 times (beta-D-xylosidase 20 times) higher than the levels detected in the adherent population from defaunated sheep. The protozoa, either directly through their own enzymes or indirectly as a consequence of their effects on the population size and activity of the other fibrolytic micro-organisms present, have an important role in determining the level of activity of polysaccharide-degrading enzymes in the rumen ecosystem. Although the extent of ryegrass (Lolium perenne) hay digestion was similar after 24 h in the absence or presence of protozoa, the initial ruminal degradation was higher in refaunated sheep.

Ammonia↗
PubMed1991

Influence of CO2 and low concentrations of O2 on fermentative metabolism of the ruminal ciliate Polyplastron multivesiculatum.

The effects of ruminal concentrations of CO2 and oxygen on the end products of endogenous metabolism and fermentation of D-glucose by the ruminal entodiniomorphid ciliate Polyplastron multivesiculatum were investigated. The principal metabolic products were butyric, acetic, and lactic acids, H2, and CO2. 13C nuclear magnetic resonance spectroscopy identified glycerol as a previously unknown major product of D-[1-13C]glucose fermentation by this protozoan. Metabolite formation rates were clearly influenced by the headspace gas composition. In the presence of 1 to 3 microM O2, acetate, H2, and CO2 formation was partially depressed. A gas headspace with a high CO2 content (66 kPa) was found to suppress hydrogenosomal pathways and to favor butyrate accumulation. Cytochromes were not detected (less than 2 pmol/mg of protein) in P. multivesiculatum; protozoal suspensions, however, consumed O2 for up to 3 h at 1 kPa of O2. Under gas phases of greater than 2.6 kPa of O2, the organisms rapidly became vacuolate and the cilia became inactive. The results suggest that fermentative pathways in P. multivesiculatum are influenced by the O2 and CO2 concentrations that prevail in situ in the rumen.

Animals↗
PubMed1990

Identification of the pertussis toxin-sensitive G proteins in platelets, megakaryocytes, and human erythroleukemia cells.

Guanine nucleotide-binding regulatory proteins, or G proteins, mediate the interaction of agonist receptors on the platelet surface with phospholipase C and adenylyl cyclase. To better understand this process, we have used several approaches to identify which G proteins are present in platelets, normal human megakaryocytes, and human erythroleukemia (HEL) cells, a leukemic cell line with megakaryocytic features. Because platelet and HEL cell responses to thrombin are inhibited by pertussis toxin, we have focused upon the members of the Gi family, whose alpha subunits can be ADP-ribosylated by that toxin. Western blots with antisera specific for Gi alpha demonstrated the presence in both platelets and HEL cells of the three best-described forms of this protein: Gi alpha 1, Gi alpha 2, and Gi alpha 3. Based upon immunoprecipitation studies with [35S]-methionine-labeled HEL cells, their relative abundance appears to be Gi alpha 2 much greater than Gi alpha 3 greater than Gi alpha 1. A HEL cell cDNA library screened with the Gi alpha antisera produced clones encoding Gi alpha 2 and Gi alpha 3 that had sequences similar to those reported from other sources. Gi alpha-specific probes created from these cDNA clones confirmed the presence of mRNA encoding Gi alpha 2 and Gi alpha 3 in both platelets (by Northern blotting) and megakaryocytes (by in situ hybridization). Thus the pertussis toxin substrates that have previously been detected in platelets and HEL cells are shown to be members of the Gi alpha family, all of which are candidates for interaction with receptors for thrombin and other agonists.

Adenylate Cyclase Toxin↗
PubMed1990

Hydrogenosomes in the rumen entodiniomorphid ciliate Polyplastron multivesiculatum.

The rumen entodiniomorphid ciliate protozoon Polyplastron multivesiculatum was shown, by biochemical and electron microscopic techniques, to possess hydrogenosomes. After differential centrifugation of whole cell homogenates the hydrogenosomal marker enzymes pyruvate:ferredoxin oxidoreductase and hydrogenase were recovered predominantly (61% and 70% of activity respectively) in the large granular fractions that were sedimented by centrifugation for 10(4) g-min (fraction P1) and 10(5) g-min (fraction P2). These subcellular fractions contained membrane-bound organelles that were approximately 0.4-0.6 microns in diameter and which had a mean equilibrium density of 1.22-1.24 g ml-1 after isopycnic centrifugation in sucrose gradients. Malate dehydrogenase (decarboxylating) activity, however, was predominantly non-sedimentable after centrifugation for 6 x 10(6) g-min. Numerous hydrogenosome-like organelles were present in the ectoplasm and endoplasm of the cell. Hydrogenase activity was demonstrated and localized in the protozoan cell using a novel staining procedure with distyryl nitroblue tetrazolium chloride (DSNBT).

Animals↗
PubMed1990

Effect of Methanobrevibacter smithii on Xylanolytic Activity of Anaerobic Ruminal Fungi.

Three different ruminal anaerobic fungi, Neocallimastix frontalis PNK2, Sphaeromonas communis B7, and Piromonas communis B19, were grown axenically or in coculture with Methanobrevibacter smithii on xylan. N. frontalis and S. communis in monoculture and coculture accumulated xylobiose, xylose, and arabinose in the growth medium; arabinose was not metabolized, but xylobiose and xylose were subsequently used. The transient accumulation of xylose was much less evident in cocultures. Both the rate and extent of xylan utilization were increased by coculturing, and metabolite profiles became acetogenic as a result of interspecies hydrogen transfer; more acetate and less lactate were formed, while formate and hydrogen did not accumulate. For each of the three fungi, there were marked increases in the specific activities of extracellular xylanase (up to fivefold), alpha-l-arabinofuranosidase (up to fivefold), and beta-d-xylosidase (up to sevenfold) upon coculturing. The stimulating effect on fungal enzymes from coculturing with M. smithii was independent of the growth substrate, and the magnitude of the stimulation varied according to the enzymes and the incubation time. For an N. frontalis-M. smithii coculture, the positive stimulation was maintained during an extended (18-day) incubation period, and this affected not only hemicellulolytic enzymes but also polysaccharidase and glycoside hydrolase enzymes that were not involved in xylan breakdown. The specific activity of cell-bound endopeptidase was not increased under the coculture conditions used in this study. The higher enzyme activities in cocultures are discussed in relation to catabolite repression.

Journal Article↗