Effects of Estrogen on Relaxation Rates in Rat Caudal Artery

SummaryRidogrel (6.3 × 10−6 to 10−4 M) inhibited contractions of isolated rat caudal arteries and rabbit femoral arteries caused by U-46619. The slope of an Arunlakshana-Schild plot (pA2-value: 3.4 × 10−6 M) on the caudal artery was slightly higher than one (1.14). This effect was maximal within}D min of incubation of the blood vessel with the compound and easily reversible. Ridogrel antagonised contractions of isolated rabbit femoral arteries caused by prostaglandin Fzo2α in the same concentration range. Ridogrel also inhibited contractions induced by aggregating rat platelets on isolated rat caudal arteries (itt the presence of ketanserin 4 × 10−7 M) and on isolated rabbit pulmonary and femoral arteries (in the absence of ketanserin). Ridogrel had no effect on Ca2+-induced contractions in depolarised isolated rabbit femoral arteries, and at 10−4 M antagonised serotonin-induced contractions in this blood vessel. Its effect on serotonin-induced contractions was statistically significant but very small on isolated rat caudal arteries. These observations indicate that ridogrel is an antagonist of prostaglandin endoperoxide/thromboxane A2 and prostaglandin F2α raCeptors on vascular smooth muscle.

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Improved Contrast in Ultra-Low-Field MRI with Time-Dependent Bipolar Prepolarizing Fields: Theory and NMR Demonstrations

Metrology and Measurement Systems ◽

10.2478/mms-2013-0028 ◽

2013 ◽

Vol 20 (3) ◽

pp. 327-336 ◽

Cited By ~ 3

Author(s):

Jaakko O. Nieminen ◽

Jens Voigt ◽

Stefan Hartwig ◽

Hans Jürgen Scheer ◽

Martin Burghoff ◽

...

Keyword(s):

Field Strength ◽

Time Course ◽

Signal Strength ◽

Relaxation Rates ◽

Resonance Imaging ◽

New Approach ◽

Spin Lattice ◽

Low Field ◽

Low Field Mri ◽

Magnetic Resonance Imaging Mri

Abstract The spin-lattice (T1) relaxation rates of materials depend on the strength of the external magnetic field in which the relaxation occurs. This T1 dispersion has been suggested to offer a means to discriminate between healthy and cancerous tissue by performing magnetic resonance imaging (MRI) at low magnetic fields. In prepolarized ultra-low-field (ULF) MRI, spin precession is detected in fields of the order of 10-100 μT. To increase the signal strength, the sample is first magnetized with a relatively strong polarizing field. Typically, the polarizing field is kept constant during the polarization period. However, in ULF MRI, the polarizing-field strength can be easily varied to produce a desired time course. This paper describes how a novel variation of the polarizing-field strength and duration can optimize the contrast between two types of tissue having different T1 relaxation dispersions. In addition, NMR experiments showing that the principle works in practice are presented. The described procedure may become a key component for a promising new approach of MRI at ultra-low fields

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Structure and Dynamics of Spherical and Rodlike Alkyl Ethoxylate Surfactant Micelles Investigated Using NMR Relaxation and Atomistic Molecular Dynamics Simulations

10.26434/chemrxiv.8044235.v1 ◽

2019 ◽

Author(s):

Allison Edwards ◽

Abdolreza Javidialesaadi ◽

Katie Weigandt ◽

George Stan ◽

Charles Eads

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulations ◽

Nmr Relaxation ◽

Cross Relaxation ◽

Relaxation Rates ◽

Surfactant Micelles ◽

Cylindrical Micelles ◽

Spherical Micelles ◽

Dynamics Simulations ◽

Relative Motions

We study molecular arrangements and dynamics in alkyl ethoxylate nonionic surfactant micelles by combining high field (600 and 700 MHz) NMR relaxation measurements with large-scale atomistic molecular dynamics simulations. For spherical micelles, but not for cylindrical micelles, cross relaxation rates are positive only for surfactant alkyl tail atoms connected to the hydrophilic head group. All cross relaxation rates are negative for cylindrical micelles. This effect is reproducible either by changing composition (ratios of the nonionic surfactants) or changing temperature of a single surfactant in order to change the micelle shape. We validate the micelle shape by SANS and use the results as a guide for our simulations. We calculate parameters that determine relaxation rates directly from simulated trajectories, without introducing specific functional forms. Results indicate that relative motions of nearby atoms are liquid-like, in agreement with 13C T1 measurements, though constrained by micelle morphology. Relative motions of distant atoms have slower components because the relative changes in distances and angles are smaller when the moving atoms are further apart. The slow, long-range motions appear to be responsible for the predominantly negative cross relaxation rates observed in NOESY spectra. The densities of atoms from positions 1 and 2 in the boundary region are lower in spherical micelles compared to cylindrical micelles. Correspondingly, motions in this region are less constrained by micelle morphology in the spherical compared to the cylindrical cases. The two effects of morphology lead to the unusual occurrence of positive cross relaxation involving positions 1 and 2 for spheres.

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Mixing rates for potentials of non-summable variations

Ergodic Theory and Dynamical Systems ◽

10.1017/etds.2021.65 ◽

2021 ◽

pp. 1-18

Author(s):

CHRISTOPHE GALLESCO ◽

DANIEL Y. TAKAHASHI

Keyword(s):

Invariance Principle ◽

Type Inequality ◽

Upper Bounds ◽

Decay Of Correlations ◽

Relaxation Rates ◽

Weak Invariance Principle ◽

Weak Invariance ◽

Coupling Inequality ◽

Mixing Rates

Abstract Mixing rates, relaxation rates, and decay of correlations for dynamics defined by potentials with summable variations are well understood, but little is known for non-summable variations. This paper exhibits upper bounds for these quantities for dynamics defined by potentials with square-summable variations. We obtain these bounds as corollaries of a new block coupling inequality between pairs of dynamics starting with different histories. As applications of our results, we prove a new weak invariance principle and a Hoeffding-type inequality.

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Changes in electromyographic activity, mechanical power, and relaxation rates following inspiratory ribcage muscle fatigue

Scientific Reports ◽

10.1038/s41598-021-92060-y ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Antonio Sarmento ◽

Guilherme Fregonezi ◽

Maria Lira ◽

Layana Marques ◽

Francesca Pennati ◽

...

Keyword(s):

Muscle Fatigue ◽

Low Frequency ◽

Mechanical Power ◽

Electromyographic Activity ◽

Median Frequency ◽

Relaxation Rates ◽

Shortening Velocity ◽

Inspiratory Muscles ◽

Underlying Mechanisms

AbstractMuscle fatigue is a complex phenomenon enclosing various mechanisms. Despite technological advances, these mechanisms are still not fully understood in vivo. Here, simultaneous measurements of pressure, volume, and ribcage inspiratory muscle activity were performed non-invasively during fatigue (inspiratory threshold valve set at 70% of maximal inspiratory pressure) and recovery to verify if inspiratory ribcage muscle fatigue (1) leads to slowing of contraction and relaxation properties of ribcage muscles and (2) alters median frequency and high-to-low frequency ratio (H/L). During the fatigue protocol, sternocleidomastoid showed the fastest decrease in median frequency and slowest decrease in H/L. Fatigue was also characterized by a reduction in the relative power of the high-frequency and increase of the low-frequency. During recovery, changes in mechanical power were due to changes in shortening velocity with long-lasting reduction in pressure generation, and slowing of relaxation [i.e., tau (τ), half-relaxation time (½RT), and maximum relaxation rate (MRR)] was observed with no significant changes in contractile properties. Recovery of median frequency was faster than H/L, and relaxation rates correlated with shortening velocity and mechanical power of inspiratory ribcage muscles; however, with different time courses. Time constant of the inspiratory ribcage muscles during fatigue and recovery is not uniform (i.e., different inspiratory muscles may have different underlying mechanisms of fatigue), and MRR, ½RT, and τ are not only useful predictors of inspiratory ribcage muscle recovery but may also share common underlying mechanisms with shortening velocity.

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Properties of Silicone Rubber-Based Composites Reinforced with Few-Layer Graphene and Iron Oxide or Titanium Dioxide

Polymers ◽

10.3390/polym13101550 ◽

2021 ◽

Vol 13 (10) ◽

pp. 1550

Author(s):

Vineet Kumar ◽

Anuj Kumar ◽

Minseok Song ◽

Dong-Joo Lee ◽

Sung-Soo Han ◽

...

Keyword(s):

Magnetic Properties ◽

Titanium Dioxide ◽

Iron Oxide ◽

Stress Relaxation ◽

Silicone Rubber ◽

Room Temperature ◽

Relaxation Rates ◽

Layer Graphene ◽

Few Layer Graphene ◽

Mechanical Actuation

The increasing demand for polymer composites with novel or improved properties requires novel fillers. To meet the challenges posed, nanofillers such as graphene, carbon nanotubes, and titanium dioxide (TiO2) have been used. In the present work, few-layer graphene (FLG) and iron oxide (Fe3O4) or TiO2 were used as fillers in a room-temperature-vulcanized (RTV) silicone rubber (SR) matrix. Composites were prepared by mixing RTV-SR with nanofillers and then kept for vulcanization at room temperature for 24 h. The RTV-SR composites obtained were characterized with respect to their mechanical, actuation, and magnetic properties. Fourier-transform infrared spectroscopy (FTIR) analysis was performed to investigate the composite raw materials and finished composites, and X-ray photoelectron spectroscopy (XPS) analysis was used to study composite surface elemental compositions. Results showed that mechanical properties were improved by adding fillers, and actuation displacements were dependent on the type of nanofiller used and the applied voltage. Magnetic stress-relaxation also increased with filler amount and stress-relaxation rates decreased when a magnetic field was applied parallel to the deformation axes. Thus, this study showed that the inclusion of iron oxide (Fe3O4) or TiO2 fillers in RTV-SR improves mechanical, actuation, and magnetic properties.

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Mechanistic study of solvent exchange reactions of manganese(II), iron(II), nickel(II), copper(II), and iron(III) ions in bulky 1,1,3,3-tetramethylurea (TMU) solvent by measurements of oxygen-17 NMR relaxation rates and chemical shifts: Complexation reaction of nickel(II) ion in TMU and crystal structure of [Ni(tmu)5](BPh4)2

Inorganica Chimica Acta ◽

10.1016/j.ica.2005.08.011 ◽

2006 ◽

Vol 359 (2) ◽

pp. 511-518 ◽

Cited By ~ 4

Author(s):

Ken-ichiro Tanada ◽

Akira Hashimoto ◽

Hiroaki Tsuji ◽

Kaoru Kato ◽

Yasuhiro Inada ◽

...

Keyword(s):

Crystal Structure ◽

Chemical Shifts ◽

Nmr Relaxation ◽

Mechanistic Study ◽

Complexation Reaction ◽

Solvent Exchange ◽

Relaxation Rates ◽

Exchange Reactions

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Diethylstilbestrol Modifies the Structure of Model Membranes and Is Localized Close to the First Carbons of the Fatty Acyl Chains

Biomolecules ◽

10.3390/biom11020220 ◽

2021 ◽

Vol 11 (2) ◽

pp. 220

Author(s):

Alessio Ausili ◽

Inés Rodríguez-González ◽

Alejandro Torrecillas ◽

José A. Teruel ◽

Juan C. Gómez-Fernández

Keyword(s):

Membrane Surface ◽

Water Layer ◽

Fatty Acyl ◽

31P Nmr Spectroscopy ◽

Relaxation Rates ◽

X Ray Diffraction ◽

Scanning Calorimetry ◽

X Ray ◽

Acyl Chains ◽

Dynamics Simulations

The synthetic estrogen diethylstilbestrol (DES) is used to treat metastatic carcinomas and prostate cancer. We studied its interaction with membranes and its localization to understand its mechanism of action and side-effects. We used differential scanning calorimetry (DSC) showing that DES fluidized the membrane and has poor solubility in DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) in the fluid state. Using small-angle X-ray diffraction (SAXD), it was observed that DES increased the thickness of the water layer between phospholipid membranes, indicating effects on the membrane surface. DSC, X-ray diffraction, and 31P-NMR spectroscopy were used to study the effect of DES on the Lα-to-HII phase transition, and it was observed that negative curvature of the membrane is promoted by DES, and this effect may be significant to understand its action on membrane enzymes. Using the 1H-NOESY-NMR-MAS technique, cross-relaxation rates for different protons of DES with POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) protons were calculated, suggesting that the most likely location of DES in the membrane is with the main axis parallel to the surface and close to the first carbons of the fatty acyl chains of POPC. Molecular dynamics simulations were in close agreements with the experimental results regarding the location of DES in phospholipids bilayers.

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