Formation of rodlike structures of water between oppositely charged ions in decane and polyethylene.

The Gibbs ensemble Monte Carlo method has been combined with the connectivity altering osmotic Gibbs ensemble to study water solubility and clustering in decane and polyethylene. We show that the presence of oppositely charged ion pairs that have fixed positions in the hydrocarbon matrices leads to an order of magnitude increase in the water solubility. This is important to a wide range of technical applications, since the uptake of the water leads to an increase in volume--or expansion--of the hydrocarbon phase which, in the case of polyethylene, may change the polymer properties and lead to water treeing. The increase in solubility is largest when the ions are sufficiently close so that rod-shaped clusters of water molecules form between the ions.

Water absorption in polyethylene under external electric fields.

Monte Carlo simulations of the solubility and structure of water in polyethylene in thermodynamic equilibrium with liquid water were performed in external fields ranging from 2 x 10(5) to 4 x 10(9) V/m. For a given equilibrium temperature and pressure, the water solubility decreases at higher fields. This occurs since it is energetically favorable for water molecules to be in the pure water phase than in the polyethylene matrix at high field strengths, and results in an increased density in the water phase. However, fields relevant to high voltage conduction (in the absence of defects that can lead to large local field strengths) do not change the solubility. In addition, at large fields the number of water clusters decreases for all cluster sizes. The rate of decrease is highest for large clusters, and a larger fraction of water molecules exist as monomers in the polyethylene matrix at high fields. Large fields also cause alignment of the water molecules, which leads to more clusters with linear topologies and hence an increase in the cluster radius of gyration.

Monte Carlo simulations of equilibrium solubilities and structure of water in n-alkanes and polyethylene.

Gibbs ensemble Monte Carlo methods based on a force field that combines the simple point charge [Berendsen et al., in Intermolecular Forces, edited by Pullman (Reidel, Dordrecht, 1981), p. 331] and transferable potentials for phase equilibria [Martin and Siepmann, J. Phys. Chem. B 102, 2659 (1998)] models were used to study the equilibrium properties of binary systems consisting of water and n-alkanes with chain lengths from hexane to hexadecane. In addition, systems where extended linear alkane chains (up to 300 carbon units long) were used to represent amorphous polyethylene were simulated in the presence of water using a connectivity altering osmotic Gibbs ensemble. In these simulations the equilibrium between a liquid water phase and a polymer phase into which water was inserted was studied. The predicted solubilities, which were determined between 350 and 550 K, are in good agreement with experiment, where experimental results are available, and the density of water molecules in the hydrocarbons is approximately 63% as high as in saturated water vapor under the same conditions. At the lower temperatures most of the water exists as monomers; increasing the temperature leads to an increase in the density of water in the alkane phase and hence in the fraction of molecules that participate in clusters. Dimers are the most prevalent clusters in all hydrocarbons and at all temperatures studied, and the fraction of clusters of given size decrease with increasing cluster size. A large fraction of trimers, tetramers, and pentamers, which are the cluster sizes for which topologies have been studied, are cyclic at low temperatures, but at higher temperatures linear structures predominate. The same properties are observed for pure water vapor clusters in equilibrium with the liquid phase, showing that the cluster topologies are not significantly affected by the surrounding hydrocarbon.

Failure of current guidelines for cholesterol screening in urban African-American adolescents.

OBJECTIVE: The National Cholesterol Education Program (NCEP) and the American Academy of Pediatrics recommend selective screening to detect children and adolescents with hypercholesterolemia. We compared the effectiveness of these guidelines with other potential screening strategies in urban African-American adolescents. SUBJECTS AND METHODS: Two hundred sixty African-American adolescents and young adults (192 females and 68 males; age range, 12 to 20 years) who were free from illnesses or medications that disrupt lipid metabolism were included in the study. Participants completed a questionnaire regarding their smoking habits, blood pressure, contraceptive pill use, and family history of early heart disease and high cholesterol and had their blood lipids, lipoproteins, and apolipoproteins measured (152 fasting and 108 nonfasting). RESULTS: Nineteen percent of participants reported family histories of hypercholesterolemia; 26% reported family histories of premature heart disease; and 8% had family histories of both hypercholesterolemia and premature heart disease. Therefore, 37% of these participants would have been targeted for cholesterol screening, compared with the 25% predicted by the NCEP. Less than 50% of the participants with low-density lipoprotein cholesterol (LDL-C) levels greater than 110 or 130 mg/dL would have been detected by selective screening. Total cholesterol was superior as a screening test to apolipoprotein B in predicting LDL-C levels greater than 110 mg/dL (sensitivity, 92% vs 59%). However, total cholesterol minus high-density lipoprotein cholesterol showed better positive predictive value (100%) at LDL-C levels greater than 110 mg/dL than total cholesterol in the fasting (80%) and total groups (90%). CONCLUSIONS: In this population, selective screening with total cholesterol, as recommended by the NCEP, has such poor sensitivity and positive predictive value that other options may be superior. As an alternative, we recommend the measurement of high-density lipoprotein cholesterol together with total cholesterol at the initial screening step in adolescents and universal screening for those older than 16 years to capture a greater proportion of young adults with increased LDL-C. Furthermore, we recommend using the less stringent treatment guidelines established by the Adult Treatment Panel II for premenopausal women and men younger than 35 years for older adolescents and young adults.

Felodipine versus placebo in stable effort-induced angina pectoris in patients inadequately controlled with metoprolol--a dose-finding study.

We compared the antianginal and antiischemic effect and tolerability of four different doses of felodipine extended-release (ER) tablets with placebo in patients with stable effort-induced angina pectoris treated with beta-blocker [metoprolol controlled release (CR) 100 mg once daily, o.d.]. Seventy-five patients were enrolled in the study. At the end of a 2-week single-blind period, all patients performed two exercise tests. If total exercise time did not vary by > 15% between the two tests and both tests were limited by anginal discomfort and concomitant ST depression of at least 1 mm, the patients were randomized to double-blind treatment (66 patients). Each patient received three of the following treatments: felodipine 2.5, 5, 10, or 20 mg, or placebo. The treatments were given o.d. in a cross-over, balanced incomplete block design with three of 3-week treatment periods. Exercise tests were performed 12 and 24 h after dose intake at the end of each treatment period. Fifty-nine patients completed the study. Twelve hours after dose administration, 10 and 20 mg felodipine increased time to onset of anginal pain by 60 and 63 s on the average, respectively, as compared with placebo (p = 0.001). Time to 1-mm ST depression was prolonged by 29 s after 10 mg (p = 0.14) and by 30 s after 20 mg (p = 0.13) felodipine. Time to end of exercise was increased by 28 s (p = 0.07) and 15 s (p > 0.20), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular dynamics simulation of a phospholipase A2-substrate complex.

We have used knowledge of the three-dimensional structure of phospholipids and phospholipases A2 together with biochemical data, computer graphics modelling and a 48 ps molecular dynamics simulation to predict the structure of a phospholipase A2-substrate complex. There is remarkable similarity between this predicted structure of enzyme-substrate complex and the structure that can be deduced from the observed enzyme-inhibitor complex. Molecular dynamics simulation highlights the importance of the calcium-ion in substrate binding and the persistence of the His-48 to water-hydrogen bond is compatible with the proposed role of this water molecule as the nucleophile in catalysis.

Pelvic inflammatory disease in the adolescent: comparison of transabdominal and transvaginal sonographic evaluation.

Transabdominal (TA) and transvaginal (TV) sonograms (n = 116) were obtained in 84 patients aged 12-21 years (mean, 16.2 years) with the clinical diagnosis of acute pelvic inflammatory disease (PID). The studies were compared for image quality and unique diagnostic information. TV sonography demonstrated superior resolution of 25 dilated fallopian tubes. Heterogeneous pelvic masses, described as tubo-ovarian abscesses on TA sonograms, could be separated on TV sonograms into various stages of PID including pyosalpinx, hydrosalpinx, tubo-ovarian complex, and tubo-ovarian abscess. Thirty-one TA and TV studies were normal despite patients fulfilling strict clinical criteria for PID. The level of severity of PID, as determined at TA sonography, was altered in 28 cases, with medical therapy changed in 23 cases because of additional TV sonographic findings. TV sonography provided superior anatomic detail in the evaluation of patients with PID, demonstrating abnormalities that were not seen at TA sonography in 71% of patients.

Common menstrual disorders.

Clinically significant PMS is experienced infrequently by young girls and adolescents. It becomes more prevalent as women get older and is reported in up to 40 per cent of older women. To date, the etiology and underlying pathophysiologic mechanisms leading to symptoms of PMS have not been identified. Although multiple treatments are utilized, randomized double-blind crossover studies have failed to confirm the benefit of any one regimen. Most adolescents should be managed with reassurance and dietary and exercise modifications rather than with medication.

The kinetics of calcium binding to calmodulin: Quin 2 and ANS stopped-flow fluorescence studies.

The rate of calcium dissociation from bovine testis calmodulin was measured by fluorescence stopped-flow using the calcium indicator Quin 2 or the fluorescence probe 8-anilinonaphthalene sulphonate. Two processes are resolved with Quin 2 corresponding to dissociation from the high affinity sites (kdiss 2 to 9 s-1 for T = 11 to 28 degrees C) and from the low affinity sites (kdiss 293 to 550 s-1 for T = 11 to 19 degrees C). These rates and the activation parameters as determined for the slow process delta H not equal to = 59 +/- 10 kJ X mol-1 and delta S not equal to = 30 +/- 30 JK-1 X mol-1 are in good agreement with values determined from the 43Ca NMR exchange rates. These experiments provide confirmation that the calcium induced conformational change cannot be resolved kinetically from the calcium binding or dissociation, and by inference this conformational change is not a rate-limiting process in the function of calmodulin.

[Differention of the neural tube. Experimental study in chick and quail embryos]. / Differenzierung des Neuralrohres. Experimentelle Untersuchungen an Hühner- und Wachtelembryonen

In order to study the possible influence of adjacent structures upon differentiation and proliferation of the chick spinal cord, a piece of neural tube of chick embryos incubated for 2 days (stages 12-14 of HAMBURGER and HAMILTON) was extirpated and replaced by an equal graft from a donor embryo of the same age. The grafts were rotated 90 or 180 degrees around their longitudinal axis. The examination of the serial histological sections and the analysis of the distribution of mitotic density in the rotated spinal cord of embryos fixed 2-8 days after the operation led to the following results: the differences in morphogenesis and histogenesis between dorsal and ventral sectors of the spinal cord are already determined in 2-day-old chick embryos. The reversal of the neural tube at this time has no effect either upon the typical differentiation or the characteristic distribution of the mitotic cells in the spinal cord.

Cyclic AMP and adenylate cyclase in the inner ear.

The activity of adenylate cyclase and the steady state levels of cyclic AMP (cAMP) were determined in stria vascularis (SV) and organ of Corti (OC) of the guinea pig cochlea. The activities are 12 and 19 pmoles/mg dry weight/minute for OC and SV, respectively. The activity was increased two to four-fold by NaF. The base level of cAMP is 4.2 and 4.4 nmoles/g dry weight in OC and SV, respectively. In contrast to brain, neither ischemia nor barbiturates produced major changes of the steady state levels of cAMP. No in vitro effect of cAMP upon the state of activation of glycogen phosphorylase was noticeable in either tissue. cAMP did not exert a significant in vitro inhibition of strial Na+K+-ATPase. Perilymphatic perfusion of cAMP (10-3 M) and of theophylline (5 times 10-3 M) did not produce changes in the endolymphatic potential (EP), but dibutyryl cAMP (10-3 M) led to a significant increase of EP. The alpha adrenergic blocking agent, phentolamine, produced very complex changes of the cochlear potentials. A possible role of catecholamines and cAMP in the secretory phenomena of the SV and in the transduction and/or transmission processes of the auditory sense organ are discussed.