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Biomedical subjects

C Eng

Publications and source records attributed to C Eng.

At least 55 records · Page 3Linked to original sources
PubMed1991

Isolation and characterization of insoluble collagen of dog hearts.

A procedure for isolating insoluble heart collagen has been developed. The method involves the use of defined optimal conditions of sonication that yield no thermal denaturation of the triple-helical structure nor disruption of the primary structure of the collagen molecules; this is followed by extraction of isolates with nondenaturing agents. The amino acid residues of the isolates are then reacted with dansyl chloride to allow determination of amino-terminal residues and quantification of the collagen. The method has several advantages over existing procedures: (i) There is no other method available for isolation of undenatured insoluble heart collagen in almost pure form (consists of 96% of type I collagen) and in a good yield. Sonication of tissue at or below 4 degrees C for a total of 120 s (15 s sonication repeated 8 times at 120-s intervals) yielded insoluble collagen fibers with 90% yield and a 20-fold purification as determined by the increase in Hyp content of the isolates. Extraction of these isolates with 0.6 M KCl and 1 M NaCl at 4 degrees C resulted in a 22-fold purification with 70% yield, while the classical extraction method with nondenaturing reagents yielded only 5-fold purification. (ii) There has been little study of the derivatization of an insoluble protein (collagen) with dansyl chloride. The Lys residues of collagen could be recovered as epsilon-Dns-Lys in 84% yield from a reverse-phase C-18 column by high-performance liquid chromatography. This assay allows measurement of 0.1-100 nmol epsilon-Dns-Lys. (iii) The method generates direct information concerning the quantity of collagen and its nature with respect to amino groups.

Animals↗
PubMed1990

Elevated creatine kinase and malignancy.

Increased serum levels of CK isoenzymes variously signal heart, brain, or skeletal muscle damage. They may also be markers for advanced tumors with poor prognosis.

Biomarkers, Tumor↗
PubMed1989

ACE inhibitors in acute and chronic ischaemia: current status and future promise.

1. Myocyte loss, reactive hypertrophy, dynamic ischaemia with 'stunning', and ventricular wall remodelling are all involved in the initiation and progression of myocardial failure which is ischaemic in origin. 2. The effects of ACE inhibitors to reduce preload and afterload has potentially salutary effects in these settings. Moreover, sulphyl containing ACE inhibitors may have further actions in reducing free radicals and their damage in the acute phases of these events. 3. These promising initial studies warrant further exploration.

Acute Disease↗
PubMed1989

Standardization of yeast inocula with an electronic impedance counter.

The standardization of yeast inocula has been identified as an important variable in the performance of reproducible in vitro fungal susceptibility testing. We investigated the precision and accuracy of an electronic particle counter in preparing yeast inocula, with quantitative culture used as a "gold standard." Suspensions of Candida albicans and Torulopsis glabrata standardized with a particle counter at 10(6) counts per ml were highly reproducible when cultured quantitatively (coefficients of variation, 6.7 and 6.8%, respectively). Accuracies of particle counts, compared with those of quantitative culture, were -8.5 and +2.8% for the two species, respectively. Electronic cell counts were highly linear between 5 X 10(6) and 5 X 10(4) CFU/ml (R2 greater than 0.99). Multiple electronic counts of a single suspension of C. albicans had less variation than did multiple quantitative cultures of a suspension of the same organism (coefficients of variation, 2.4 versus 8.9%; P less than 0.01), suggesting that impedance counting is probably more precise than quantitative culture. Electronic particle counters can be used to prepare accurate, reproducible yeast inocula. The method may be more accurate and is more precise than other techniques commonly used to standardize yeast suspensions.

Colony Count, Microbial↗
PubMed1988

The effects of acutely increased ventricular cavity pressure on intrinsic myocardial connective tissue.

Studies of normal hearts have revealed a variety of intrinsic connective tissue structures that surround and interconnect myocytes and ventricular mural layers. Among these structures, springlike coiled perimysial fibers, arrayed parallel to myocytes in the interstitial space, have been described in papillary muscle and ventricle. To evaluate the role of the coiled perimysial fibers under perturbed conditions, rat ventricles were filled with barium-gelatin under different pressures and fixed, and then the myocardium was impregnated with silver to visualize the connective tissue. Ventricles were filled at 30, 70 and 100 to 120 mm Hg. The coiled perimysial fibers were studied for their orientation, stretch, integrity and relation to sarcomere length. The coils were noted to embed within the fibrous anulus and to knot into an umbilical-like mass at the apex, thus anchoring them at both ends of the ventricle. They underwent focal straightening even at 30 mm Hg, with generalized straightening and disruption at the highest pressure; changes were most pronounced in the midventricle. Sarcomeres were maintained below 2.2 micron at 30 and 70 mm Hg of cavity pressure in regions of coiled perimysial fiber stretch; only with fiber disruption at 100 to 120 mm Hg were sarcomeres significantly lengthened. Other findings included connective tissue disruption between ventricular wall layers that allowed slippage of myocytes and mural thinning. These observations suggest that coiled perimysial fibers may act as a buffer to protect myocytes from damage under the effects of high cavity pressure.

Animals↗
PubMed1988

Spatial heterogeneity of local blood flow and metabolite content in dog hearts.

Spatial variation (heterogeneity) of myocardial blood flow was studied under basal conditions in relation to four biochemical markers: creatine kinase (CK), lactate dehydrogenase (LDH), ATP, and glycogen. A total of 508 individual 0.5-g samples from the left ventricular free wall was studied in 12 dogs. Myocardial blood flow was measured by radioactive microspheres (15 micron diam) injected via a pigtail catheter into the left ventricle during light sedation (closed-chest flow measurements); following thoracotomy, a second set of microspheres was injected via a catheter into the left atrium (open-chest flow measurements, n = 5). In 27-54 samples/heart, myocardial blood flow, CK, LDH, protein, ATP, and glycogen were determined, permitting a direct correspondence between local blood flow and metabolic markers in each sample and an assessment of the spatial heterogeneity of flow and metabolite content. Correlations between myocardial blood flow per gram tissue and metabolite concentration per gram tissue in pooled data were weak but significant: partial correlation coefficients were 0.137 for CK (P = 0.024), 0.167 for LDH (P = 0.006), 0.341 for ATP (P less than 0.001), 0.123 for glycogen (P = 0.053), but not significant for protein vs. myocardial blood flow. The coefficient of variation, which defines the extent of spatial heterogeneity, averaged 20% for closed-chest flow measurements, 19% for open-chest flow measurements, 22% for CK, 17% for LDH, 15% for protein, 8% for ATP, and 18% for glycogen; these values are over and above the variability due to the technique error, indicating a definite physiological spatial variability. The correlation between local blood flow and the studied metabolites can only explain a minor portion of the spatial heterogeneity of myocardial blood flow. Although a physiological link between blood flow and metabolite content for small regions of the heart is demonstrated, the true local variability of blood flow may be modulated predominantly by other factors.

Adenosine Triphosphate↗
PubMed1988

Ventricular preload alters intravascular and extravascular resistances of coronary collaterals.

Coronary collateral blood flow is determined by both the collateral vessel resistance and a waterfall mechanism. The aim of this study was to determine which of these two mechanisms predominates during alteration of ventricular preload. The left anterior descending coronary artery of 12 anesthetized dogs was cannulated, and the distal vasculature was completely embolized with 25-micron diameter microspheres. Retrograde blood flow (RBF) was collected when the cannula was opened to the atmosphere, and the outflow tubing height was adjusted to provide a variable back pressure. RBF is back pressure-dependent at higher back pressures, and the slope in this region of the constructed pressure-flow relationship determines the collateral conductance. The transition point between the back pressure-dependent and a back pressure-independent region indicates a waterfall pressure impinging on the collateral vessels. At a left ventricular diastolic pressure of 9.3 mmHg, mean RBF, collateral conductance, and the collateral waterfall pressure were 7.3 ml/min, 0.175 ml.min-1.mmHg-1, and 30.1 mmHg, respectively. Corresponding values when preload was reduced to 3.5 mmHg were 9.3 ml/min, 0.186 ml.min-1.mmHg-1, and 23.7 mmHg, all changes being significant. Mean contribution to the overall increase in RBF was 0.5 ml/min for the conductance and 1.2 ml/min for the waterfall mechanism (P less than 0.05), or 29 and 71%, respectively. The results indicate that the extravascular resistance mechanism mediates the collateral flow response to a greater degree than the intravascular resistance during variations in preload. The increase in slope of the conductance portion of the relationship was not accompanied by a concomitant increase in slope of the back pressure-independent region. These data further support a collateral waterfall, and not collateral vessel compliance, as the basis for the back pressure-independent portion of the pressure-flow relationship.

Animals↗
PubMed1988

NMR studies of renal phosphate metabolites in vivo: effects of hydration and dehydration.

The present study characterizes the 31P-nuclear magnetic resonance (NMR) spectrum of rabbit kidneys in vivo and evaluates the effect of hydration on phosphorous metabolites including the organic solute glycerophosphorylcholine (GPC). Cortical phosphorylethanolamine is the predominant component of the phosphomonoester region of the 31P spectrum. The contribution of blood to the spectrum is mainly from 2,3 diphosphoglycerate, which comprises approximately 30% of the inorganic phosphate region. Acute infusion of 0.9% saline decreases the sodium content of the inner medulla by greater than 50% in 15 min as shown by 23Na imaging. Despite this medullary Na dilution, no change in renal GPC content was observed for greater than 1 h even with the addition of furosemide (2.5 mg/kg) or furosemide and antidiuretic hormone (0.125 U/kg). However, 20 h of chronic hydration with 0.45% saline did result in a 30% decrease in renal GPC content when compared with dehydrated animals. These findings are consistent with GPC not playing a role in the short-term regulation of the medullary intracellular milieu in response to acute reductions in medullary Na content.

2,3-Diphosphoglycerate↗
PubMed1988

Identification of a mutation in the structural alpha-L-fucosidase gene in fucosidosis.

Fucosidosis is an autosomal recessive lysosomal storage disorder characterized by progressive neurological deterioration and mental retardation. The disease results from deficient activity of alpha-L-fucosidase (E.C.3.2.1.51), a lysosomal enzyme that hydrolyzes fucose from fucoglycoconjugates. In an attempt to identify the mutation(s) that result(s) in fucosidosis, we performed Southern blot analysis of the structural gene encoding alpha-L-fucosidase (FUCA 1) in 23 patients affected with fucosidosis. In five patients Southern blot analysis showed obliteration of an EcoRI restriction site in the open reading frame of FUCA 1 encoding mature alpha-L-fucosidase. This abnormality was not observed in 80 controls, and it may be the basic defect responsible for fucosidosis in these patients. Both patients with the severe type I form of fucosidosis and patients with the less severe type II were shown to be homozygous for this presumed mutation. In the remaining 18 patients the EcoRI site obliteration, major-gene deletions, or insertions were not detected. This suggests that at least two different mutations are involved in fucosidosis. The heterogeneity found at the DNA level was not present at the protein level, as all fucosidosis patients investigated had low fucosidase protein (less than 6% of normal) and negligible fucosidase activity in fibroblasts and lymphoblastoid cell lines.

Blotting, Southern↗
PubMed1987

Profound structural alterations of the extracellular collagen matrix in postischemic dysfunctional ("stunned") but viable myocardium.

Ultrastructural studies of the extracellular collagen matrix were made on the "stunned" myocardium using scanning, conventional and high voltage transmission electron microscopy and light microscopy. Regional myocardial dysfunction was produced by 12 sequential 5 minute occlusions of the left anterior descending coronary artery, separated by 10 minute intervals of reperfusion. A final 90 minute reperfusion period documented persistent myocardial dysfunction. At the end of the final reperfusion period, the percent systolic shortening, measured by sonomicrometers, was depressed significantly to 35 +/- 9% of baseline. The heart was then perfusion fixed, and samples were taken from both control and stunned areas. No changes associated with irreversible cellular damage were noted in the stunned region. However, scanning electron microscopy of the stunned area showed that the extracellular collagen matrix underwent profound structural changes. Collagen cables were roughened, uncoiled and discontinuous. Linear grooves on the surface of the myocytes were frequently seen, indicating complete loss of collagen cables. The usual dense collagen weave surrounding myocytes became patchy or absent. Myocyte to myocyte struts were sparse and frequently absent, with remnant nodular or nublike structures indicative of breakage. High voltage electron microscopy of the stunned area showed that the collagen struts were discontinuous and vacuolated with rounded tips. Light microscopy of silver-stained sections of the stunned tissue demonstrated large patchy areas that were devoid of silver, indicating absence of the collagen matrix. There was a progressive increase in percent systolic bulging during each sequential coronary occlusion, suggesting increasing myocardial compliance. These results indicate that the myocardial collagen matrix is severely damaged from reversible ischemic cell injury. The greater myocardial compliance and less effective contractile effort in the stunned myocardium might be explained on a structural basis: disruption of the mechanical coupling function provided by the extracellular collagen matrix.

Animals↗
PubMed1987

A nonflow basis for the vulnerability of the subendocardium.

The functional consequences of a transmural gradient of metabolism in the heart were studied in 19 dogs. The technique of retrograde blood flow diversion after coronary occlusion was used to deplete the ischemic myocardium of blood flow. Blood flow was uniformly and equally depleted in all layers, averaging 0.044 ml/min per g. With oxygen supply a controlled variable, transmural differences in metabolic demand can be addressed. In groups of dogs severe myocardial ischemia was induced for periods of 20 to 90 minutes. No necrosis was noted after 20 minutes of ischemia. Beginning at 30 minutes of blood flow depletion, necrosis progressed from the endocardium toward the epicardium in a "wave front" pattern. At 90 minutes of ischemia, approximately 70% of the area at risk was necrotic. Thus, the relative vulnerability of the endocardium as compared with the epicardium is due to nonflow factors, and probably dictated by transmural differences in metabolic activity. It would appear that myocardial metabolism as compared with blood flow occupies a primary and overriding role during the first 20 minutes of ischemia. Furthermore, differences in transmural metabolism also dictate subendocardial vulnerability for ischemic periods greater than 20 minutes, irrespective of blood flow. The role of blood flow in these events may be to modulate the rate of the transmural wave front of progressing necrosis after 20 minutes of ischemia.

Animals↗
PubMed1985

Improvement of coronary blood flow by augmentation of coronary vascular compliance.

Coronary blood flow occurs predominantly during the diastolic period of the cardiac cycle. This study investigated the effects of increasing the diastolic coronary perfusion pressure by artificially increasing the epicardial coronary capacitance function, using a buffer chamber. The left anterior descending (LAD) coronary artery was cannulated in six dogs and perfused by tubing via the carotid artery. A significant stenosis was produced with a screw clamp, resulting in a distal coronary pressure of about 35 mm Hg. A buffer chamber was placed on the perfusion line distal to the stenosis to buffer the distal coronary perfusion pressure. Myocardial blood flow as measured by microspheres showed a 39.6% increase in blood flow during buffered perfusion as compared to nonbuffered perfusion: 0.415 +/- 0.279 versus 0.316 +/- 0.238 ml/min/g. The calculated diastolic pressure time index (DPTI) increased 54.1% during buffered perfusion. Flow increased significantly in the endocardial and mid-wall layers but not in the epicardium. It is concluded that coronary blood flow can be augmented by increasing the coronary capacitance function in this model.

Animals↗
PubMed1985

Effects of vasopressin on the coronary circulation: reserve and regulation during ischemia.

In 18 dogs, intracoronary infusion of vasopressin produced a 40% reduction in coronary flow without significantly affecting systemic hemodynamics. The blood flow reduction occurred in a uniform transmural pattern without evidence of a gradient. The reduction in coronary flow resulted in a decrease in regional contractility as determined by isometric strain gauge arches. The decrease in regional contractility was transiently reversed by bolus injection of adenosine into the perfusion line. This suggests that the reduction of blood flow due to vasopressin was causing ischemia. Evidence for ischemia was also supported by measurements of local vein and tissue lactate production. Despite the apparently ischemic conditions, the vascular bed demonstrated evidence for significant reserve and regulation. Pressure-flow relationships performed under control and during vasopressin infusion demonstrated that the coronary vasculature retained its ability to regulate or defend a given level of coronary flow over a range of coronary perfusion pressures. Vasopressin produced a mild decrease in the peak hyperemic flow after a 15-s coronary occlusion and shortened the duration of reactive hyperemia. These overall findings are compatible with a predominant vasoconstrictor effect on the distal coronary vasculature. A role for a myogenic factor in the control of the coronary circulation is suggested, which is amplified by vasopressin.

Animals↗