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Biomedical subjects

H Engelhardt

Publications and source records attributed to H Engelhardt.

At least 55 records · Page 3Linked to original sources
PubMed1990

In vitro evaluation of left ventricular assistance by cannulation of both femoral arteries.

The possibility of achieving effective mechanical ventricular assistance without the need for thoracotomy provides great clinical advantages. Two in vitro systems were used to assess left ventricular unloading by means of a small-diameter cannula inserted retrograde into the left ventricle by cannulation of the femoral artery. This cannula is connected to the inlet of a centrifugal blood pump (CP) that delivers the blood into the contralateral femoral artery. Steady-flow test circulation was used to pump fluid in a closed loop from a reservoir through the test cannula back into the reservoir. Pressure drops over cannulae with inner diameters of 4, 5, 6, 7, and 8 mm at flows of 2, 2.5, 3 L/min, against a pressure of 60, 80, 100, and 120 mmHg were calculated. A stationary pressure drop of 120 mmHg was measured at a flow of 3 L/min through a 100 cm cannula with an inner diameter of 6 mm. The second system was a pulsatile mock circulation composed of an atrial and an arterial reservoir linked by a pneumatic prosthetic ventricle. This system was coupled with a 100 cm cannula, 6.1 mm inner diameter, which was passed across the outflow valve of the pulsatile prosthetic ventricle and connected to a CP. Fluid was withdrawn from the ventricle and pumped back into the arterial reservoir. Pulsatile pressure drop over the cannula was measured at different CP flows for increasing systolic ventricular pressure; heart unloading was quantified as a function of CP flow under baseline and failing conditions of the prosthetic left ventricle model. At a constant CP flow the pressure drop over the cannula increased with the pulsatility inside the ventricle. The work of the prosthetic ventricle was reduced by more than 50% when the CP pump was set to 3 L/min; at the same flow setting, when the situation of a failing left ventricle was simulated, the CP was able to take over all the work of the prosthetic ventricle, establishing a stationary flow and a 25% higher mean aortic pressure. This approach to left ventricular assistance may have significant clinical relevance.

Assisted Circulation↗
PubMed1989

Three-dimensional structure of the surface protein layer (MW layer) of Bacillus brevis 47.

The three-dimensional (3D) structure of one surface protein layer from Bacillus brevis 47, the middle wall (MW) layer, has been reconstructed from tilted-view electron micrographs after correlation averaging to a resolution of 2 nm. The MW layer has p6 symmetry with a center-to-center spacing of 18.3 nm and a minimum thickness of 5.5 nm. The reconstruction reveals a distinct domain structure: the heavier domain of six monomers jointly forms a massive core centered at the sixfold symmetry axis, and lighter domains interconnect adjacent unit cells. In addition, the larger domains collectively form a pore by making contact with each other towards the inner surface, while the smaller domains establish a second connectivity towards the outer surface of the S layer. The MW layer of B. brevis resembles the S layer of Acetogenium kivui in various aspects: they have very similar lattice parameters and highly reminiscent 3D structures; the pores penetrate through the whole core and appear to determine the porosity of the S layers.

Bacillus↗
PubMed1989

Estradiol-induced blockade of ovulation in the cow: effects on luteinizing hormone release and follicular fluid steroids.

Administration of 10 mg estradiol valerate (EV) to nonlactating Holstein cows on Days 16 of the estrous cycle prevented ovulation in 7 of 8 cows for 14 days post-injection. In these 7 cows, the timing of luteolysis and the luteinizing hormone (LH) surge was variable but within the normal range. At 14 days post-treatment, each of these cows had a large (greater than 10 mm) follicle, with 558 +/- 98 ng/ml estradiol-17 beta, 120 +/- 31 ng/ml testosterone, and 31 +/- 2 ng/ml progesterone in follicular fluid (means +/- SE). A second group of animals was then either treated with EV as before (n = 22), or not injected (control, n = 17) and ovariectomized on either Day 17, Day 18.5, Day 20, or Day 21.5 (24, 60, 96, or 132 h post-EV). Treatment with EV did not influence the timing of luteolysis, but surges of LH occurred earlier (59 +/- 8 h post-EV vs. 100 +/- 11 h in controls). The interval from luteolysis to LH peak was reduced from 44 +/- 6 h (controls) to 6.9 +/- 1.5 h (treated). Histologically, the largest follicle in controls tended to be atretic before luteolysis, but nonatretic afterwards, whereas the largest follicle in treated animals always tended to be atretic. Nonatretic follicles contained high concentrations of estradiol (408 +/- 59 ng/ml) and moderate amounts of testosterone (107 +/- 33 ng/ml) and progesterone (101 +/- 21 ng/ml), whereas atretic follicles contained low concentrations of estradiol (8 +/- 4 ng/ml) and testosterone (12 +/- 4 ng/ml), and either low (56 +/- 24 ng/ml) or very high (602 +/- 344 ng/ml) concentrations of progesterone. This study suggests that EV prevents ovulation by inducing atresia of the potential preovulatory follicle, which is replaced by a healthy large follicle by 14 days post-treatment.

Animals↗
PubMed1989

Three-dimensional structure of an open form of the surface layer from the fish pathogen Aeromonas salmonicida.

Cell-free culture supernatants of a lipopolysaccharide (LPS) O-polysaccharide-deficient, single-insertion transposon mutant of the tetragonal surface protein array (S layer)-containing fish pathogen Aeromonas salmonicida were examined by electron microscopy. Negative staining showed that the S layer was released as sheets of tetragonal material, indicating that although surface retention of assembled S layer requires the presence of wild-type LPS oligosaccharides, initial assembly of S-layer subunits into sheets does not require the presence of O-polysaccharide chains. The three-dimensional structure of the S layer was reconstructed from tilted micrographs of the released sheets. Horizontal sections through this reconstruction showed that the released sheets were composed of two identical S layers that were perfectly in register. The reconstructed layer had a lattice constant of 12.5 nm. At a resolution of 1.6 nm, the layer consisted of a major tetragon at one fourfold axis of symmetry and a minor tetragon at the second fourfold axis of symmetry. The core, composed of four of the major domains, contained a large depression and was located toward the inside of the layer. The minor tetragon provided connectivity within the layer and was located toward the outer surface of the layer. Projections through the double layer gave a type I (closed) pattern (M. Stewart, T. J. Beveridge, and T. J. Trust, J. Bacteriol. 166:120-127, 1986), yet projections through the single layer indicated that the type II (open) pattern was present. This open pattern was indistinguishable from that seen in S layer released from the surfaces of wild-type cells.

Aeromonas↗
PubMed1989

In vitro reconstitution of a hexagonal array with a surface layer protein synthesized by Bacillus subtilis harboring the surface layer protein gene from Bacillus brevis 47.

Bacillus brevis 47 contains two surface layer proteins, termed the outer wall protein and the middle wall protein (MWP), which form a hexagonal array in the cell wall. Introduction of the MWP structural gene into Bacillus subtilis by using a low-copy-number plasmid led to the synthesis of an immunoreactive polypeptide with a molecular mass almost the same as that of the MWP synthesized by B. brevis 47. Biochemical analysis indicated that most of the MWP synthesized by B. subtilis was localized in the cytoplasmic fraction. This was further confirmed by using immunogold electron microscopy. The amino-terminal amino acid sequence of the MWP purified from the cytoplasm of B. subtilis indicated that the MWP was precursor with a signal peptide of 23 amino acid residues to the amino terminus of the mature protein. The precursor of the MWP possessed the ability to reassemble in vitro on the B. brevis 47 peptidoglycan layer, resulting in the formation of almost the same hexagonal arrays as with the mature MWP purified from B. brevis 47, judging from images averaged at a resolution of about 2.5 nm. Furthermore, a center-to-center distance of the hexagonal lattice on the envelope reconstituted by using the precursor MWP was calibrated as 18.3 nm, which was almost identical to the value of 17.8 nm obtained with the mature protein.

Amino Acid Sequence↗
PubMed1989

Mevinolin (lovastatin) inhibits androstenedione production by porcine ovarian theca cells at the level of the 17 alpha-hydroxylase:C-17,20-lyase complex.

Mevinolin, putatively a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme-A reductase, was used to assess the contribution of de novo synthesized cholesterol to androgen production by ovarian thecal cells in vitro. Enzymatically dispersed thecal cells from 3- to 6-mm follicles of prepubertal gilts were incubated at 150,000 cells/ml with a maximally effective dose of LH (250 ng/ml) for 24 h. Mevinolin (3-50 microM) caused dose-dependent inhibition of androstenedione production. Addition of 25-hydroxycholesterol (0.025-25 microM) failed to restore androstenedione production to levels seen in the absence of mevinolin, suggesting an additional site of action of mevinolin beyond 3-hydroxy-3-methylglutaryl coenzyme reductase. The site of this inhibitory effect was determined by measuring steroid products formed in the presence of relevant steroid precursors. Mevinolin (12 microM) inhibited the production of 17 alpha-hydroxyprogesterone from progesterone and that of androstenedione from 17 alpha-hydroxyprogesterone, while 25-hydroxycholesterol to progesterone and pregnenolone to progesterone conversions were unimpaired. That mevinolin did not affect 3 beta-hydroxysteroid dehydrogenase:delta 5-delta 4-isomerase reactions was confirmed by demonstrating that conversions of pregnenolone, 17 alpha-hydroxypregnenolone, and dehydroepiandrosterone to progesterone, 17 alpha-hydroxyprogesterone, and androstenedione, respectively, were not affected by 12 microM mevinolin. These results indicate that mevinolin has an additional inhibitory action at the level of the 17 alpha-hydroxylase:C-17,20-lyase complex. The degree of inhibition of androstenedione production was not decreased with increased concentrations of progesterone or 17 alpha-hydroxyprogesterone substrate, suggesting that the inhibition was not competitive in nature. As the dose of mevinolin was increased up to 50 microM, progesterone accumulation was unaffected, but pregnenolone concentrations in medium greatly increased. While the mechanism of this effect is unclear, this finding suggests that preformed intracellular cholesterol, rather than that synthesized de novo, is supplying steroidogenic substrate in these cells.

Aldehyde-Lyases↗
PubMed1988

Bacterial surface proteins. Some structural, functional and evolutionary aspects.

The structure of several eubacterial and archaebacterial surface (glyco)proteins as determined by three-dimensional electron microscopy is described. Particular emphasis is placed on surface proteins which interact with membranes. Some structure-function relationships deduced from the structural information, such as shape maintenance and molecular recognition phenomena, are discussed.

Archaea↗
PubMed1988

On the measurement of shear elastic moduli and viscosities of erythrocyte plasma membranes by transient deformation in high frequency electric fields.

We present a new method to measure the shear elastic moduli and viscosities of erythrocyte membranes which is based on the fixation and transient deformation of cells in a high-frequency electric field. A frequency domain of constant force (arising by Maxwell Wagner polarization) is selected to minimize dissipative effects. The electric force is thus calculated by electrostatic principles by considering the cell as a conducting body in a dielectric fluid and neglecting membrane polarization effects. The elongation A of the cells perpendicular to their rotational axis exhibits a linear regime (A proportional to Maxwell tension or to square of the electric field E2) at small, and a nonlinear regime (A proportional to square root of Maxwell tension or to the electric field E) at large extensions with a cross-over at A approximately 0.5 micron. The nonlinearity leads to amplitude-dependent response times and to differences of the viscoelastic response and relaxation functions. The cells exhibit pronounced yet completely reversible tip formations at large extensions. Absolute values of the shear elastic modulus, mu, and membrane viscosity, eta, are determined by assuming that field-induced stretching of the biconcave cell may be approximately described in terms of a sphere to ellipsoid deformation. The (nonlinear) elongation-vs.-force relationship calculated by the elastic theory of shells agress well with the experimentally observed curves and the values of mu = 6.1 x 10(-6) N/m and eta = 3.4 x 10(-7) Ns/m are in good agreement with the micropipette results of Evans and co-workers. The effect of physical, biochemical, and disease-induced structural changes on the viscoelastic parameters is studied. The variability of mu and eta of a cell population of a healthy donor is +/- 45%, which is mainly due to differences in the cell age. The average mu value of cells of different healthy donors scatters by +/- 18%. Osmotic deflation of the cells leads to a fivefold increase of mu and 10-fold increase of eta at 500 mosm. The shear modulus mu increases with temperature showing that the cytoskeleton does not behave as a network of entropy elastic springs. Elliptic cells of patients suffering from elliptocytosis of the Leach phenotype exhibit a threefold larger value of mu than normal discocytes of control donors. Cross-linking of the spectrin by the divalent S-H agents diamide (1 mM, 15 min incubation) leads to an eightfold increase of mu whereas eta is essentially constant. The effect of diamide is reversed after treatment with S-S bond splitting agents.

Diamide↗
PubMed1987

Structure of the porin from a bacterial stalk.

The stalks (hyphae) of a prosthecate bacterium, directly sampled from the water surface of a hot pond, show extended regular patterns on their envelope in the electron microscope. Image processing revealed a structure of the crystalline complexes which is very similar to the gross morphology of the Escherichia coli porins OmpC and OmpF. The natural two-dimensional crystal of the outer membrane protein has p3 symmetry and a lattice constant of 7.95 nm. The three-dimensional structure of the stalk porin has been determined to an almost isotropic resolution of 1.7 nm. The reconstruction revealed a complex network of channels within the membrane matrix with a triplet of pores merging into a common outlet, similar to the structure of the E. coli porin OmpF in reconstituted membranes. In addition, a blindly ending pore exists which appears to be connected to the continuous pores via small channels. The significance of the regularly arrayed porin cylinders with respect to the shape and function of the stalks is discussed.

Bacterial Outer Membrane Proteins↗
PubMed1987

Three-dimensional structure of the regular tetragonal surface layer of Azotobacter vinelandii.

Fragments of the Azotobacter vinelandii tetragonal surface (S) layer, free of outer membrane material, were obtained by treating whole cells with 100 microM EDTA. The three-dimensional structure of the S layer was reconstructed from tilted-view electron micrographs of the S-layer fragments, after computer-assisted image processing by correlation averaging. At a resolution of 1.7 nm, the S layer exhibited funnel-shaped subunits situated at one fourfold-symmetry axis and interconnected at the other fourfold-symmetry axis to form prominent cruciform linking structures. These data, in conjunction with a relief reconstruction of the surface of freeze-etched whole cells, indicated that the apex of the funnel-shaped subunit was associated with the outer membrane, while the funnel "opening" faced the environment; the cruciform linking structures were formed at the outermost surface of the S layer. Electron microscopy and image enhancement were used to compare the structure of the outer membrane-associated S layer with that of fragments of the S layer dislodged from the outer membrane. This analysis revealed an increase in the lattice constant of the S layer from 12.5 to 13.6 nm and an alteration in the position of the cruciform linking structures in the z direction. These conformational changes resulted in a reduction in the thickness of the S layer (minimum estimate, 5 nm) and an apparent increase in the size of the gaps between the subunits. In terms of the porosity of the S layer, this gave the appearance of a transition from a closed to a more open structure.

Azotobacter↗
PubMed1986

Three-dimensional structure of the tetragonal surface layer of Sporosarcina ureae.

The three-dimensional structure of the regular surface layer of Sporosarcina ureae has been determined to a resolution of 1.7 nm by electron microscopy and image reconstruction. The S-layer has p4 symmetry, a lattice constant of 12.9 nm, and a minimum thickness of 6.6 nm. The reconstruction reveals a distinct domain structure: a massive core, arms connecting adjacent unit cells, and spurs which make contact at the subsidiary fourfold symmetry axes. In the z-direction the domains appear to be arranged in three planes, creating two entirely different surface reliefs. The S-layer has a complex pattern of pores and gaps that are 2 to 3 nm wide. In addition, the secondary-structure composition has been determined by infrared spectroscopy: about 35% of the polypeptide appears to have a beta-structure conformation.

Bacterial Proteins↗
PubMed1986

Simulation of physiological ureteral peristalsis.

Occlusive ureteral peristalsis is simulated in an enlarged technical model of the ureter with a lobe-shaped lumen. The local pressure pulse is measured with catheters of different caliber and the influence of the catheters size and position on the uromanometrogram (UMG) is examined. The measurements are compared with UMGs at pathologically changed conditions (stagnation, residual urine depot etc.) and suggestions are given concerning size and shape of catheters to be used for urodynamic measurements.

Humans↗
PubMed1986

The tetragonal surface layer of Clostridium aceticum: three-dimensional structure and comparison with the hexagonal layer of Clostridium thermohydrosulfuricum.

The regular surface layer (S-layer) of Clostridium aceticum has been isolated and the three-dimensional structure determined to a resolution of 2.0 nm from tilt series of negatively stained preparations. It has tetragonal symmetry with a lattice constant of 12 nm and a thickness of 6 nm; there are probably 4 protein monomers per unit cell. A large proportion of the protein is concentrated in massive "cores" at the major four-fold axes which are situated towards the inner surface of the layer. From these cores, delicate arms extend towards the minor four-fold axes, where secondary connectivity is established near the exterior surface. When viewed from the outside, each of the cores appears to have a large central depression, rather than a true "pore". Since this general pattern of mass distribution is shared by the hexagonal S-layer of Clostridium thermohydrosulfuricum, some consideration has been given to the possible evolutionary steps leading to changes in symmetry. From modelling experiments, it is evident that the change from four-fold to six-fold symmetry in this instance could be accomplished simply by the loss of a structural "domain" from the protomer.

Bacterial Proteins↗
PubMed1986

Bloodpumps.

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Assisted Circulation↗
PubMed1979

Structure of tetanus toxin. Demonstration and separation of a specific enzyme converting intracellular tetanus toxin to the extracellular form.

Protease activity has been demonstrated in culture supernatants of Clostridium tetani at various stages of fermentation. Gel chromatography of the concentrated filtrates revealed the presence of three enzymatically active fractions eluting at separate positions off the column. The smallest protease was found to "nick" the single chain intracellular tetanus toxin, producing the extracellular, two-chain structure of the molecule. As little as 3 ng of active protease were sufficient to cleave 50 microgram of intracellular tetanus toxin, suggesting that this enzyme is responsible for the observed structural change of the toxin molecule during its release into the culture medium. By comparison, the second protease, eluting at an intermediate position, exhibited only marginal activity towards intracellular toxin. The third, largest, enzyme was not active under the conditions of the assay. However, the latter protease effectively hydrolyzed low molecular weight histidyl peptides, and it is concluded that this enzyme is similar to the one described by Miller, P.A. Gray, C.T., and Eaton, M.D. (1960) J. Bacteriol. 79, 95-102. The properties of the partially purified enzymes, including their differential behavior towards a number of protease inhibitors, are reported.

Clostridium tetani↗
PubMed1979

BCG vaccination of neonates, infants, schoolchildren and adolescents. Part I: Dose finding studies with BCG strain 1331 Copenhagen.

A BCG vaccine prepared from strain 1331 Copenhagen was given to newborns and infants in four logarithmically decreasing doses (expressed in VU = viable units): 25 X 10(4), 11 X 10(4), 5 X 10 (4), and 2.2 X 10(4). The efficacy of the vaccine was determined through the conversion rate (tuberculin skin test) with 2 and 10 T. U. of RT 23, AND 10 AND 50 I. U. of GT (Hoechst). The results indicated that the conversion rate is a function of the dose of VU of the vaccine, as well as of the units of tuberculin used for testing.

Adolescent↗