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PubMed1979

[Periodic modifications of the preoptico-terminal LRH tract in the squirrel monkey during the estrous cycle (author's transl)].

The quantities of specific immunoreactive material along the preoptico-terminal LRH tract show important modifications during the estrous cycle in the squirrel monkey. During the late follicular phase and the peri-ovulatory period the preoptico-terminal LRH tract shows "low" or "very low" fluorescence intensity. A progressive but very important increase occurs during the luteal phase, followed by great variations during the early and middle follicular phases. These variations suggest a conspicuous release of LRH, especially during the middle follicular phase. It is supposed that the preoptico-terminal LRH tract (whose LRH is released into the capillaries of the vascular organ of the lamina terminalis and reaches the systemic blood) controls gonadotropic cell sensitivity to the preovulatory discharge of the hypothalamo-infundibular LRH tract, and perhaps also gonadotropins synthesis.

Animals↗

PubMed1988

Hydrolysis of phosphatidylcholine in phosphatidylcholine-cholate mixtures by porcine pancreatic phospholipase A2.

Pancreatic phospholipase A2 (PLA2)-catalyzed hydrolysis of egg yolk phosphatidylcholine (PC) in mixed PC-cholate systems depends upon composition, structure, and size of the mixed aggregates. The hydrolysis of PC-cholate-mixed micelles made of an equal number of PC and cholate molecules is consistent with a Km of about 1 mM and a turnover number of about 120 s-1. Increasing the cholate/PC ratio in the micelles results in a decreased initial velocity. Hydrolysis of cholate-containing unilamellar vesicles is very sensitive to the ratio of cholate to PC in the vesicles. The hydrolysis of vesicles with an effective cholate/PC ratio greater than 0.27 is similar to that of the mixed micelles. The time course of hydrolysis of vesicles with lower effective ratios is similar to that exhibited by pure dipalmitoyl-phosphatidylcholine (DPPC) large unilamellar vesicles in the thermotropic phase transition region. In the latter two cases, the rate of hydrolysis increases with time until substrate depletion becomes significant. The reaction can be divided phenomenologically into two phases: a latency phase where the amount of product formed is a square function of time (P(t) = At2) and a phase distinguished by a sudden increase in activity. The parameter A, which describes the activation rate of the enzyme during the initial phase in a quantitative fashion, increases with increasing [PLA2], decreasing [PC], decreasing vesicle size, and increasing relative cholate content of the vesicles. The effect of [PLA2] and [PC] on the hydrolysis reaction is similar to that found with pure DPPC unilamellar vesicles in their thermotropic phase transition region. The effect of cholate on the hydrolysis reaction is similar to that of temperature variation within the phase transition of temperature variation within the phase transition of DPPC. These results are consistent with our previously proposed model, which postulates that activation of PLA2 involves dimerization of the enzyme on the substrate surface and that the rate of activation is directly proportional to the magnitude of lipid structural fluctuations. It is suggested that large structural fluctuations, which exist in the pure lipid system in the phase transition range, are introduced into liquid crystalline vesicles by the presence of cholate and thus promote activation of the enzyme.

1,2-Dipalmitoylphosphatidylcholine↗

PubMedDate not supplied

Pattern-reversal electroretinogram in response to chromatic stimuli: I. Humans.

We have studied the steady-state PERG in human subjects in response to red-green plaid patterns modulated either in luminance or in chromaticity or both. By varying the relative luminance of the red and green components, a value could be obtained at which the PERG amplitude was either minimum or locally maximum. This always occurred at equiluminance, as measured by standard psychophysical techniques. PERG amplitude and phase were measured as a function of spatial and temporal frequency of sinusoidal contrast reversal. In both space and time, the response to chromatic patterns was low-pass, while that to luminance was band-pass, and extended to higher spatial and temporal frequencies. The phase of the PERG to chromatic stimuli was systematically lagged compared with that to luminance stimuli, by an amount corresponding to about 20 ms under our experimental conditions. The variation of phase with temporal frequency suggested an apparent latency of about 67 ms for color contrast compared with 47 ms for luminance. These estimates were confirmed with separate measurements of transient PERGs to abrupt contrast reversal. For both luminance and chromatic stimuli, the amplitude of PERGs increases with increasing stimulus contrast. By summing vectorially the responses to appropriate luminance and chromatic contrasts, we were able to predict with accuracy the response as a function of color ratio (ratio of red to total luminance). The above findings all agree with those reported in the accompanying paper for the monkey PERG (Morrone et al., 1994), and indicate that the differences in response latency and integration time of luminance and chromatic stimuli observed by psychophysical and VEP techniques may arise at least in part from the properties of retinal mechanisms.

Color Perception↗

PubMed1988

Value of subcutaneous fat in predicting ovulation day.

Subcutaneous body fat and Quetelet's Indices (QI) of 52, 18-29 year old normal female volunteers were determined. These body mass indices were then grouped according to the phase of each subject's menstrual cycle, early or late follicular and early or late luteal phase. The subcutaneous body fat is 27.07 +or- 1.0% in the early follicular but drops to 24.68 +or- 1.84% in the late follicular phase. The value then rises significantly higher than that in the late follicular phase to 30.14 +or- 1.15% (P0.02) in the early luteal drops to 27.17 +or- 0.55% towards the level of the early follicular phase (P0.05). Variations in the values of QI during each menstrual cycle exactly mirror those for subcutaneous body fat. The fall in the 2 body mass indices during the late follicular phase coincides somewhat with the established preovulatory LH and FSH surges as well as the high levels of estrogen of this period. On the other hand the significant rise in the 2 parameters during the early luteal phase coincides with the marked rise in the ratio of progesterone to estrogen. Clearly, increased levels of progesterone relative to estrogen appear to cause an increase in the body fat during each menstrual cycle. The implication of this finding for women on contraceptive pills which are predominantly progesterone and those whose normal menstrual cycle is "interrupted" at the early luteal phase by a successful fertilization raises very interesting questions with regards to prediction of ovulation.

Anthropometry↗

PubMed2005

Ion-pair mediated transport of angiotensin, neurotensin, and their metabolites in liquid phase microextraction under acidic conditions.

This paper discusses the behaviour of angiotensin 1 and neurotensin together with their metabolites in a three-phase liquid phase microextraction under acidic conditions. Variations in donor phase, organic phase, and acceptor phase are studied with extraction recovery as response variable. It is proved that for all peptides the transport across the organic phase is mediated by heptane-1-sulphonic acid. n-Octanol gave overall best results as organic phase. A donor phase volume of 1.0 mL was chosen as a compromise between optimal recovery and robustness of the LPME device. The optimal pH of the donor phase (using acceptor phase of pH 2) was found to be different for the peptides, which opens opportunities for selective sample preparation. Decreasing the acceptor phase pH to 1.0 resulted in increased extraction recoveries. On using 1.0 mL of donor phase containing 50 mM heptane-1-sulphonic acid pH 3, n-octanol as organic phase immobilized in the pores of the fibre, and 20 microL of acceptor phase containing 0.1 mol/L HCl, extraction recoveries up to 82% (enrichment factor = 41) were achieved. To our knowledge this is the first report on liquid phase microextraction of angiotensins and neurotensins.

Angiotensins↗

PubMed1991

Interpretation of the surface brightness of Phobos.

Analysis of disk resolved images of Phobos obtained by the Phobos 2 spacecraft allows us to study the surface scattering law and albedo variations. From low phase angle images we find variations in local geometric albedo approximately 10%, with a correlation length approximately 1km. The scattering law is reasonably well matched by the recent proposed LPI (Lumme et al. 1990a) model, which allows us to deduce a small scale (approximately 1 mm) surface roughness (approximately 0.5), defined here as the rms. tangent of the local surface normal relative to the mean surface normal in the Duxbury (1991) model of Phobos. This value is very close to what has been found for Mercury and the Moon.

Astronomy↗

PubMed2002

Capillary electrochromatography of peptides on a column packed with tentacular weak cation-exchanger particles.

Silica-based, tentacular weak cation-exchanger particles were prepared for use as the stationary phase in the separation of positively charged sample components by capillary electrochromatography (CEC). Silica beads were first silanized with 3-(trimethoxysilyl) propyl methacrylate that served as a heterobifunctional linker, which reacted with 2-acrylarmidoglycolic acid in a second step by radical polymerization in aqueous solution. Baseline separation of basic peptides with good column efficiency was obtained on packed capillary columns by isocratic elution CEC with NaCl as the mobile phase modulator. The retention mechanism in the electrochromatographic process was studied by examining the effect of salt concentration on the migration behavior of the peptides. The chromatographic retention factor k'(lc) for charged sample components in the electrochromatographic process was estimated on the assumption that the overall migration rate of a charged migrant can be taken as the sum of the rate of chromatographic elution and the rate of electrophoretic migration. The estimated k(lc) values from experimental results were plotted against the molal salt concentration on a double logarithmic scale. The linear correlation is in good agreement with the prediction by the theory on the basis of traditional ion-exchange chromatography. The comparison of CEC results, obtained with open tubular and packed capillary columns having the same retentive functions as the stationary phase, supports the notion that variation of the phase ratio in the column offers an additional means to modulate the electrochromatographic migration behavior.

Cation Exchange Resins↗

PubMed2002

Effects of temperature on retention of chiral compounds on a ristocetin A chiral stationary phase.

The isocratic retention of enantiomers of chiral analytes, i.e. tryptophan, 1,2,3,4-tetrahydroisoquinoline and gamma-butyrolac tone analogs, was studied on a ristocetin A chiral stationary phase at different temperatures and with different mobile phase compositions, using the reversed-phase, polar-organic and normal-phase modes. By variation of the both mobile phase composition and the temperature, baseline separations could be achieved for these enantiomers. The retention factors and selectivity factors for the enantiomers of all investigated compounds decreased with increasing temperature. The natural logarithms of the retention factors (ln k) of the investigated compounds depended linearly on the inverse of temperature (1/T). van't Hoff plots afforded thermodynamic parameters, such as the apparent change in enthalpy (deltaH(o)), the apparent change in entropy (deltaS(o)) and the apparent change in Gibbs free energy (deltaG(o) ) for the transfer of analyte from the mobile to the stationary phase. The thermodynamic parameters (deltaH(o), deltaS(o) and deltaG(o)) were calculated in order to promote an understanding of the thermodynamic driving forces for retention in this chromatographic system.

Ristocetin↗

PubMedDate not supplied

Pattern-reversal electroretinogram in response to chromatic stimuli: II. Monkey.

We have recorded steady-state PERGs from five macaque monkeys in response to red-green plaid patterns reversed sinusoidally in contrast. The patterns had either a pure luminance contrast (red-black, green-black, yellow-black), pure red-green color contrast, or a variable amount of luminance and color contrast. By varying the relative luminance of the red-to-total luminance (color ratio) of red-green patterns, a value could be obtained at which the PERG amplitude was either minimum or locally maximum, and the phase was most lagged. This value was very similar to that producing equiluminance in human observers, and was considered to be equiluminance for the monkey. The phase of the PERG to chromatic stimulus was systematically lagged compared with that of luminance stimuli, by an amount corresponding to about 10-20 ms under our experimental conditions. The variation of phase with temporal frequency suggested an apparent latency of about 80 ms for color contrast compared with 63 ms for luminance. These estimates were confirmed with separate measurements of transient PERGs to abrupt contrast reversal. As a function of temporal frequency, the chromatic PERG function was clearly low-pass with a cutoff around 15 Hz, whereas that to luminance was double-peaked and extended to higher temporal frequencies, around 30 Hz. For both luminance and chromatic stimuli, the amplitude of PERGs increases with increasing stimulus contrast. By summing vectorially the luminance and chromatic responses of appropriate contrasts, we were able to predict with accuracy the response as a function of color ratio. In two monkeys, the optic chiasm was sectioned sagittally causing total degeneration of ganglion cells in the nasal retina, without affecting the temporal retina (verified by histology). In these animals, there was a strong response to both luminance and chromatic patterns in the temporal retinae, but none to either type of pattern in the nasal retinae, suggesting that the PERG to both luminance and chromatic stimuli arises from the inner-retinal layers. Electrophysiological studies suggest that the PERG to chromatic stimuli is probably associated with the activity of P-cells. P-cells may also make a major contribution to the PERG of luminance stimuli, although M-cells may also participate. The above findings on normal monkeys all agree with those reported in the accompanying paper for humans (Morrone et al., 1994), so similar conclusions can probably be extended to human PERG.

Animals↗

PubMed2005

Phase behavior of 2,3-disubstituted methyl octadecanoate monolayers at the air-water interface.

The phase behavior of 2,3-disubstituted methyl octadecanoate monolayers at the air-water interface is studied by film balance and a Brewster angle microscope (BAM). The comparison of the surface pressure-molecular area (pi-A) isotherms with the corresponding BAM images provides information on the phase behavior of the monolayers. Variations in the phase behavior of different 2,3-disubstituted methyl octadecanoate monolayers can be correlated with the size of the headgroups, the interactions between the polar molecular moieties and the subphase, and the intermolecular interactions. The enlarging of the headgroups makes forming a condensed monolayer difficult for the molecules, even after introduction of substituents giving rise to the formation of hydrogen bonds between the molecules, which may balance the steric repulsion and stabilize the monolayers. Model calculations of the two-dimensional lattice structure of the 2,3-disubstituted methyl octadecanoates on basis of the pg and p1 space group are performed and correspond well with the experimental results.

Air↗

PubMed1995

Nonlinear analysis of oscillatory flow, with a nonzero mean, in an elastic tube (artery).

Oscillatory flow of a Newtonian fluid in an elastic tube, which is a model of blood flow in arteries, is analyzed in this paper. For a rigid tube, the steady flow field can be described by Poiseuille's law and the unsteady flow field by Womersley's solution. These are the linearized solutions for flow in elastic tubes. To evaluate the importance of nonlinear effects, a perturbation solution is developed realizing that the amplitude of arterial wall movement is small (typically 5-10 percent of the diameter). The nonlinear effects on the amplitude of the wall shear rate, on the amplitude of the pressure gradient, and on the mean velocity profile have been considered. Nonlinear effects on the oscillatory components depend on Womersley's unsteadiness parameter (alpha), the ratio between the mean and amplitude of the flow rate, the diameter variation, and the phase difference between the diameter variation and the flow rate (phi) which is indicative of the degree of wave reflection. On the other hand, the mean velocity profile is found to be dependent on the steady-streaming Reynolds number, Rs. When Rs is small, the mean velocity profile is parabolic (1-xi 2); however, when Rs is large, the velocity profile is distorted by the nonlinear effect and can be described by sin (pi xi 2). The increase of the amplitude and reduction of the mean of wall shear rate as phi changes from 0 to -90 deg suggests an indirect mechanism for the role of hypertension in arterial disease: hypertension-->increased wave reflection-->wall shear stress is reduced and more oscillatory.

Arteries↗

PubMed1994

Size-disparity correlation in stereopsis at contrast threshold.

Contrast thresholds for 75% correct depth identification in narrow-band filtered random dot stereograms were determined for different center spatial frequencies and binocular disparities. Rigorous control over vergence was maintained during testing, and a forced-choice procedure was used. The resulting contrast sensitivity function for stereopsis revealed sensitivity over a greater range of disparities at low than at high spatial frequencies. Sensitivity peaked for large disparities at low spatial frequencies and for small disparities at high spatial frequencies. When disparities were converted to effective binocular phase differences, the variation of contrast sensitivity with phase followed a consistent pattern across spatial frequencies, with peak sensitivity occurring mainly for binocular phases of between 90 degrees and 180 degrees. These results have implications for the extent of spatial integration at the input to the disparity sensing mechanism. A model postulating a spread of positional disparities independent of the spatial frequency selectivity of disparity-sensitive units cannot account for the results. But the size-disparity correlation strongly evident in our data is predicted by certain models of stereopsis, such as phase disparity encoding. An ideal observer analysis is developed that demonstrates that our results were not forced by the nature of the stimulus employed; rather, the quantum efficiency for stereopsis at contrast threshold follows the size-disparity correlation.

Contrast Sensitivity↗

PubMed2006

[Toxicogenetics and toxicogenomics. Relevance and application in occupational health].

Xenobiotic metabolising enzymes modify most organic compounds into water soluble compounds. Sequence variations of these enzymes can lead to significant interindividual differences in the metabolism of xenobiotics. This review covers important sequence variations of phase I (cytochrome P450) and phase II (glutathion S-transferases, N-acetyltransferases, sulfotransferases, UDP-glucuronosyl transferases) enzymes and elucidates the significance for occupational health. At the present time, the determination of various sequence variations is not suitable for an individual risk assessment in occupational health.

Acetyltransferases↗

PubMed2000

Estimates of the daily phase and amplitude of the endogenous component of the circadian rhythm of core temperature in sedentary humans living nychthemerally.

Fifteen healthy female subjects were studied for eight days while living conventionally. Subjects were free to choose the ways they spent their time within a framework of regular times of retiring and rising; in practice, much of the waking time was spent in sedentary activities. Nine of the subjects were aware of the natural light-dark cycle, this approximating to a 12:12 L:D schedule at the time of year when the study took place. Before the study, subjects were assessed for their degree of "morningness" by questionnaire; throughout the study, they wore a rectal probe, and an activity meter on their non-dominant wrist. The timing (phase) and amplitude of the circadian rectal temperature rhythm were assessed on each day by cosinor analysis as well as by a method based on visual inspection of the data. These two parameters were also assessed after the temperature data for each day had been "purified" by a number of methods. From these results it was possible to investigate the effect of purification upon the amplitude of the circadian rhythm of temperature. Also, the day-by-day variability of phase, and the relationship between morningness and phase, were compared using these methods of phase estimation, and using cross-correlation between data sets from adjacent days; in all cases, raw and purified temperature data were used. There was a significantly greater amount of daily variation in phase using purified rather than raw data sets, and this difference was present with all methods of purification as well as with all methods for estimating phase. Purification decreased the amplitude of the circadian temperature rhythm by about 30%. Finally, there was a significant correlation between the morningness score of the subjects and the phase of the circadian temperature rhythm, the phase becoming earlier with increasing morningness; when this relationship was re-examined using purified data, it became more marked. These results reflect the masking effects exerted upon raw temperature data by lifestyle. The extent to which the purification methods enable the endogenous component of a circadian rhythm - and, by implication, the output of the endogenous circadian oscillator - to be estimated in subjects living normally is addressed.

Activities of Daily Living↗

PubMed1992

[Importance of physical parameters for the effectiveness of radiofrequency catheter ablation].

Radiofrequency catheter ablation has been shown to be an effective form of treatment of accessory pathways in patients with WPW-syndrome and other supraventricular tachycardias. However, the biophysical parameters so far used in vivo neither correlated with the size of the myocardial lesion nor did they provide any information about contact of the electrode with the myocardial wall. In this study, 104 radiofrequency energy applications were performed on excised pig myocardium in circulating heparinized pig blood, and in blood alone, and root mean square (rms) voltage, current and phase angle were measured using a specially developed device. The calculated effective power and output power differed by only 2-7% measured at the point of maximum current during coagulation. A progressive drop in current following a rise in impedance led to a phase shift of more than 80 degrees with a decrease in effective power to 17% of the output power. Hence, apparent output power was mainly ineffective power. The time-dependent variations of phase angle, impedance and current were found to be useful for distinguishing between the coagulated media. These results show that physical parameters measured during radio-frequency catheter ablation may help to monitor electrode position in the clinical situation and reduce the number of ineffective energy applications.

Animals↗

PubMed1992

Biophysical parameters of radiofrequency catheter ablation.

Radiofrequency catheter ablation has been shown to be an effective treatment for patients with accessory pathways in Wolff-Parkinson-White syndrome and other supraventricular tachycardias. However, the biophysical parameters used so far in vivo did not correlate to the size of myocardial lesions and provided no information about the myocardial wall contact of the electrode. In this study 104 radiofrequency applications were performed on excised pig myocardium in circulating heparinized pig blood as well as in blood alone, and root mean square (rms) voltage, root mean square current and phase angle were measured using a specially developed device. The calculated effective power and output power differed by only 2-7% when measured at the point of maximum current during coagulation. A drop of current following a rise in impedance led to a phase displacement of more than 80 degrees and thereby to a drop of effective power to 17% of the output power. Hence, apparent output power consists mainly of ineffective power. The time dependent variations of phase angle, impedance and current were found to be useful for distinguishing between the media blood and myocardium. These results show that physical parameters measured during radiofrequency catheter ablation may help to control electrode position in the clinical situation and reduce the number and duration of ineffective energy applications.

Animals↗

PubMed1982

Phase analysis of the first pass radionuclide angiocardiogram.

Fifty-two subjects with suspected coronary artery disease were studied by first pass radionuclide angiocardiography using a single crystal gamma camera. Phase analysis, a new technique which can detect ventricular regions with abnormal emptying patterns, was applied to the resulting left ventricular radionuclide angiocardiograms. Eighteen turned out be normal and in these subjects the variation of phase values in each of eight ventricular segments was established. Thirty-four had coronary artery disease. By comparison with the normal subjects, 21 had at least one segment with an abnormally high phase value. Such high values were associated with low values of ejection fraction, as determined by a radionuclide technique, total occlusion of a major coronary artery and significant wall motion abnormalities on the radiographic ventriculogram. A comparison between phase analysis and wall motion on a regional basis disclosed progressively high phase values with increasing severity of wall motion abnormality. Particularly high values were found in association with ventricular aneurysm. Phase analysis of first pass radionuclide angiocardiograms is a valid method for the detection of regional abnormalities of ventricular contraction in coronary artery disease.

Adult↗

PubMed2000

The phosphatidylcholine to phosphatidylethanolamine ratio of Saccharomyces cerevisiae varies with the growth phase.

This study compares the effect of the growth phase on the phospholipid composition and the activity of several phospholipid biosynthetic enzymes in a wild-type yeast grown in fermentable (glucose) and non-fermentable (lactate) semi-synthetic and complete synthetic media. Several distinct differences as well as similarities were found. The cellular phosphatidylcholine: phosphatidylethanolamine (PC:PE) ratio was found to vary with the growth phase, with increases in PC levels at the expense of PE during the transition to stationary phase. The variation was most pronounced in semi-synthetic lactate medium, which is routinely used for the isolation of mitochondria, where the PC:PE ratio changed from 0.9 to 2.2 during this transition. Similar growth phase-dependent changes in PC and PE content were observed in isolated organelles such as mitochondria, mitochondria-associated membranes and microsomes. Phosphatidylinositol (PI) levels were much higher in cells grown on lactate compared to cells grown on glucose (20% vs. 5-10%). Irrespective of the medium, PI levels increased upon entering stationary phase. The activities of the phospholipid biosynthetic enzymes phosphatidylserine synthase and the phospholipid-N-methyltransferases were found to be maximal at the end of logarithmic growth and to decrease upon entering stationary phase in all media. Cells grown on lactate displayed a significantly higher phospholipid:protein ratio than cells grown on glucose. The results are discussed in terms of regulation of phospholipid biosynthesis and membrane biogenesis in response to growth phase and carbon source.

Carbon↗