Development of a Gaussian Process - feature selection model to characterise (poly)dimethylsiloxane (Silastic® ) membrane permeation

OBJECTIVES

The current study aims to determine the effect of physicochemical descriptor selection on models of polydimethylsiloxane permeation.

METHODS

A total of 2942 descriptors were calculated for a data set of 77 chemicals. Data were processed to remove redundancy, single values, imbalanced and highly correlated data, yielding 1363 relevant descriptors. For four independent test sets, feature selection methods were applied and modelled via a variety of Machine Learning methods.

KEY FINDINGS

Two sets of molecular descriptors which can provide improved predictions, compared to existing models, have been identified. Best permeation predictions were found with Gaussian Process methods. The molecular descriptors describe lipophilicity, partial charge and hydrogen bonding as key determinants of PDMS permeation.

CONCLUSIONS

This study highlights important considerations in the development of relevant models and in the construction and use of the data sets used in such studies, particularly that highly correlated descriptors should be removed from data sets. Predictive models are improved by the methodology adopted in this study, notably the systematic evaluation of descriptors, rather than simply using any and all available descriptors, often based empirically on in vitro experiments. Such findings also have clear relevance to a number of other fields.

Model fitting for small skin permeability data sets: hyperparameter optimisation in Gaussian Process Regression

OBJECTIVES

The aim of this study was to investigate how to improve predictions from Gaussian Process models by optimising the model hyperparameters.

METHODS

Optimisation methods, including Grid Search, Conjugate Gradient, Random Search, Evolutionary Algorithm and Hyper-prior, were evaluated and applied to previously published data. Data sets were also altered in a structured manner to reduce their size, which retained the range, or 'chemical space' of the key descriptors to assess the effect of the data range on model quality.

KEY FINDINGS

The Hyper-prior Smoothbox kernel results in the best models for the majority of data sets, and they exhibited significantly better performance than benchmark quantitative structure-permeability relationship (QSPR) models. When the data sets were systematically reduced in size, the different optimisation methods generally retained their statistical quality, whereas benchmark QSPR models performed poorly.

CONCLUSIONS

The design of the data set, and possibly also the approach to validation of the model, is critical in the development of improved models. The size of the data set, if carefully controlled, was not generally a significant factor for these models and that models of excellent statistical quality could be produced from substantially smaller data sets.

Measurement of the decay rate of single-frequency perturbations on blast waves

To explore the validity of theories forwarded to explain the dynamics of hydrodynamic perturbations on high Mach number blast waves, we have studied the decay rate of perturbations on blast waves traveling through nitrogen gas. In our experiments, 1 kJ pulses from the Z-Beamlet laser at Sandia National Laboratories illuminated solid targets immersed in gas and created blast waves. The polytropic index implied by comparing experiment to theoretical predictions is compared to simulation results.

Normal exercise blood pressure response in African-American women with parental history of hypertension

BACKGROUND

Genetic and environmental hypotheses may explain why normotensive persons at high risk of developing hypertension often exhibit greater cardiovascular reactivity to stressors than those at low risk.

METHODS

Pearson's correlation was used to evaluate reproducibility and independent t test to compare the cardiovascular responses to 30 W of exercise of normotensive young adult African-American women with positive and negative parental histories (PH) of hypertension (PH, n = 23; PH, n = 20).

RESULTS

Correlations were significant for duplicate measurements. The effects of PH on blood pressure measured at rest and during exercise were not statistically significant (P > 0.1). A nearly significant trend for greater resting (.-)VO(2) (P = 0.08) was detected in the PH than in the PH group (3.67 +/- 0.18 versus 3.26 +/- 0.14 mL/kg/min).

CONCLUSION

A hyper-reactive blood pressure response to exercise, characteristic of the evolution of hypertension, may not be present among the normotensive female offspring of hypertensive African Americans. The significance of an 11% intergroup difference in the mean resting (.-)VO(2) observed in this study is unclear.

Demonstration of radiation symmetry control for inertial confinement fusion in double Z-pinch hohlraums

Simulations of a double Z-pinch hohlraum, relevant to the high-yield inertial-confinement-fusion concept, predict that through geometry design the time-integrated P2 Legendre mode drive asymmetry can be systematically controlled from positive to negative coefficient values. Studying capsule elongation, recent experiments on Z confirm such control by varying the secondary hohlraum length. Since the experimental trend and optimum length are correctly modeled, confidence is gained in the simulation tools; the same tools predict capsule drive uniformity sufficient for high-yield fusion ignition.

Symmetric inertial-confinement-fusion-capsule implosions in a double-z-pinch-driven hohlraum

An inertial-confinement-fusion (ICF) concept using two 60-MA Z pinches to drive a cylindrical hohlraum to 220 eV has been recently proposed. The first capsule implosions relevant to this concept have been performed at the same physical scale with a lower 20-MA current, yielding a 70+/-5 eV capsule drive. The capsule shell shape implies a polar radiation symmetry, the first high-accuracy measurement of this type in a pulsed-power-driven ICF configuration, within a factor of 1.6-4 of that required for scaling to ignition. The convergence ratio of 14-21 is to date the highest in any pulsed-power ICF system.

Physical activity and blood pressure responsiveness to the cold pressor test in normotensive young adult African-American males

The aim of our study was to examine whether there is an association between blood pressure reactivity to the cold pressor test in African Americans who engaged in different levels of physical activity. We examined the systolic pressure, diastolic pressure, mean arterial blood pressure, heart rate, cardiac index, total peripheral resistance, and forearm blood flow during a two-minute cold pressor test in 15 aerobic, physically active and 15 physically inactive, normotensive young adult African-American males. Peak oxygen consumption varied as a function of physical activity, and was significantly higher in the physically active than in the physically inactive subjects (54.5 +/- 1.5 vs 36.8 +/- 0.7 ml kg(-1) min(-1)) (P<.05). During the cold pressor test, consisting of immersing the foot in ice water, the change in cardiovascular responses were similar between the physically active and the physically inactive groups. These results suggest that regular physical activity may not contribute to an attenuated blood pressure response to behavioral stress of the cold pressor test in normotensive young adult African-American males.

Effect of trap position, habitat, and height on the capture of pepper maggot flies (Diptera: Tephritidae)

Trapping results indicate that pepper maggot, Zonosemata electa (Say), flies occupy tree canopies adjacent to fields when not on host plants. Several in- and near-field trap positions were used to find a reliable monitoring system for adult pepper maggots. Traps baited with liquid ammonium hydroxide (Stills-style trap), hung in the canopy of trees on the edges of pepper fields, caught significantly more Z. electa flies than when positioned lower along the treeline or in the field. In a second experiment, significantly more pepper maggot flies were captured in sugar maples compared with choke cherry trees, which indicates a pest preference for certain nonhost habitats. The lowest trap height tested (2.1 m) failed to capture Z. electa flies in either tree species when the pest population level was low. These studies demonstrated that pepper maggot flies can be reliably detected with Stills-style traps positioned at approximately 6.4 m height within the canopy of sugar maple trees adjacent to pepper fields. Fruit oviposition scars also are useful site-specific indicators of pepper maggot presence/absence and may aid in determining if insecticide applications are necessary and in timing sprays.

Aerobic exercise attenuates blood pressure reactivity to cold pressor test in normotensive, young adult African-American women

Exaggerated blood pressure reactivity to behavioral stress has been observed in the African-American population, and such a pressor response is believed to play a role in hypertension. Regular aerobic exercise has been shown to exert an anti-hypertensive effect, and this may alter the blood pressure hyperreactivity observed in African Americans. To test the hypothesis that aerobic exercise attenuates pressor reactivity in African Americans, we studied eight healthy aerobically-trained normotensive African-American females and five similar sedentary females. The stress stimuli consisted of the cold pressor test with the foot immersed in ice water for two minutes. The aerobic exercise training protocol consisted of six weeks of jogging at 60-70% of peak oxygen uptake (VO2peak), three days/week for 35 min/exercise session. Systolic blood pressure, diastolic blood pressure, mean arterial blood pressure, heart rate, cardiac output, total peripheral resistance, and forearm blood flow were measured. Manifestation of a training effect was illustrated by a 24.1 +/- 0.2% increase in VO2peak (26.9 +/- 1.2 mL x kg(-1) min(-1) vs 35.4 +/- 1.6 mL x kg(-1) min(-1)) (P<.05). Within the exercise-trained group there was a 6.3 +/- .15% decrease in systolic pressure (129 +/- 4.6 mm Hg vs. 121 +/- 5.4 mm Hg) (P<.05), and a 5.0 +/- .05% decrement in mean arterial blood pressure (99 +/- 3.3 mm Hg vs 94 +/- 3.6 mm Hg) (P<.05) during the cold pressor test. Pressor reactivity to cold stress did not change in the untrained group. Measures of heart rate, cardiac output, total peripheral resistance, and forearm blood flow were unaltered during conditions of the cold pressor test. We conclude that aerobic exercise attenuates the blood pressure reactivity to behavioral stress in young, adult normotensive African-American females. A lifestyle change such as exercising may play a role in reducing the risk of hypertension in African-American women.

Racial differences in minimum lower leg vascular resistance in normotensive young adults with positive and negative parental histories of hypertension

OBJECTIVE

To determine whether peripheral hemodynamic differences exist in young adult normotensive African Americans and white Americans with a positive and negative parental history of hypertension.

METHODS

The participants were healthy men of whom 13 were African Americans and nine white Americans with a positive parental history and 19 were African Americans and 13 white Americans with a negative parental history. Lower leg blood flows were obtained at rest and during reactive hyperemia. Lower leg minimum vascular resistance (Rmin) was computed from reactive hyperemic blood flow measured by venous occlusion plethysmography, and mean arterial blood pressure was determined by auscultation of the brachial artery.

RESULTS

Resting blood flow and mean arterial pressure were similar in all groups. A significant race x parental history interaction effect was observed for lower leg Rmin. In the white men the lower leg Rmin was significantly greater in the positive than the negative parental group (P < 0.05). Lower leg Rmin was significantly greater in African Americans than in white men without a parental histoy (P < 0.05). Mean arterial blood pressure and heart rate were similar among the groups.

CONCLUSIONS

This study demonstrates that lower leg Rmin is greater in young white men with a positive parental history of hypertension than those with a negative parental history. In African Americans with either positive or negative parental histories, lower leg Rmin is not different. This finding suggests that heredity may have a greater influence in white populations than in African Americans on the structural changes in resistance vessels. The study also suggests that African Americans have an earlier structural change in the resistance vessels compared with white people, regardless of a parental history of hypertension. This suggests that factors other than heredity are of importance in changing the structure of the resistance vessels.

Lower leg high-intensity resistance training and peripheral hemodynamic adaptations

High-intensity resistance (HIR) training has been associated with muscle hypertrophy and decreased microvascular density that might produce a blood flow limitation. The effect of HIR training on lower leg maximal blood flow and minimum vascular resistance (Rmin) during reactive hyperemia were investigated in 7 healthy males. The gastrocnemius-soleus muscles of one leg were trained using maximal isokinetic concentric contractions for 4 weeks; the nontrained leg was the control. Lower leg blood flow was measured by venous occlusion plethysmography. Lower leg muscle volume was determined using magnetic resonance imaging. Peak isokinetic torque increased in both the trained (T) and nontrained (NT) legs (p < .05). Lower leg muscle volume increased by 2% in the T leg only (p < .05). In the T leg, maximal blood flow decreased and Rmin increased (p < .05); no hemodynamic change was detected in the NT leg. It is concluded that HIR training of the calf muscles is associated with a decrease in hyperemia-induced blood flow; thereby, indicating a blood flow limitation to the calf muscles.

Structure-activity relationships within a series of C(7)-substitutedoxyiminocephalosporins containing the C(3)-methylaminopyridiniumthiomethyl substituent. Synthesis and biological properties of BRL 57342 and some close analogues

(6R,7R)-7-[2-(2-Amino-4-thiazolyl)-2-[(Z)-[(S)-carboxy(3,4- dihydroxyphenyl)methyl]oxyimino]acetamido]-3-(1-methylaminopyri dinium-4-thiomethyl)ceph-3-em-4-carboxylate sodium salt (BRL 57342, 1f) combines excellent in vitro antibacterial potency against Gram-positive and Gram-negative bacteria, including P. aeruginosa and Acinetobacter spp., with excellent stability to extended spectrum beta-lactamases. This potency is reflected in in vivo efficacy studies.

Synthesis and biological properties of some 3-[(N-substituted-amino)pyridinium-4-thiomethyl]-7-[2-(2-amino-thiazol- 4-yl)-2-(Z)-(methoxyimino)acetamido]ceph-3-em-4-carboxylates

The synthesis and antibacterial activity of a series of beta-lactamase stable, broad spectrum 7-[2-(2-amino-thiazol-4-yl)-2-(Z)-(methoxyimino)acetamido]-cephalo sporins, characterised by a C-3-[N-(substituted-amino)pyridinium-4-thiomethyl] group, is described. Gram-positive and Gram-negative bacteria including extended spectrum beta-lactamase-producing strains were most susceptible to the N-amino- and N-methylamino derivatives (3a) and (3b); with the exception of Pseudomonas aeruginosa, (3b) was more active in vitro and in vivo than cefpirome or ceftazidime.

Synthesis and biological activity of 3-(N-substituted pyridinium-4-thiomethyl)-7 alpha-formamido cephalosporins

The synthesis and antibacterial activity of a series of 3-(1-substituted pyridinium-4-thiomethyl)-7 alpha-formamido cephalosporins is described. All the derivatives showed good potency and stability to bacterial beta-lactamases. The antibacterial efficacy seen with the N-alkyl pyridinium substituents was enhanced by the introduction of a catecholic side chain at C-7 and by preparation of N-(substituted amino)pyridinium derivatives.

Evaluation of the Colin STBP-680 at rest and during exercise: an automated blood pressure monitor using R-wave gating

The application of automated blood pressure measurement during exercise has been limited by inaccuracies introduced by the effects of accompanying motion and noise. We evaluated a newly developed automated blood pressure monitor for measuring exercise blood pressure (Colin STBP-680; Colin, San Antonio, Texas, USA). The STBP-680 uses acoustic transduction with the assistance of the electrocardiogram R-wave to trigger the sampling period for blood pressure measurement. The automated monitor readings were compared with simultaneous technician mercury sphygmomanometric readings in the same arm. Blood pressure was measured in 18 men at rest and during exercise at 40% VO2 peak, (low intensity), 70% VO2 peak (moderate intensity) and VO2 peak (high intensity) on the cycle ergometer. Mean(s.d.) systolic blood pressure difference between the automated monitor and mercury manometer readings at rest and during exercise at low, moderate and high work intensities were 3(0) mmHg, 3(2) mmHg, 1(1) mmHg, and 0(11) mmHg respectively (analysis of variance; P > 0.05). Resting diastolic blood pressure obtained with the STBP-680 was similar to the mercury manometer readings (78(10) versus 81(7) mmHg (P > 0.05). Exercise diastolic pressure at the low level of work intensity was almost identical between the automated monitor and mercury manometer readings (64(8) versus 65(10) mmHg (not significant)). Diastolic blood pressure readings between the STBP-680 and mercury manometer showed a greater difference at the moderate and high workloads (11 mmHg and 9 mmHg, respectively), but this difference was not significant (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of active and passive recovery on lactate removal and subsequent isokinetic muscle function

The effect of active and passive recovery on the removal of accumulated blood lactate and subsequent muscle function were tested using five male subjects. The experimental protocol consisted of two exercise sessions performed on a mechanical brake cycle ergometer at 150% VO2max for 60 seconds. Termination of the supramaximal work bouts were followed by a 20 minutes active recovery period cycling at 30% VO2max and a 20 minutes passive recovery period sitting quietly. Following the recovery modes, isokinetic measures of peak torque, total work output and fatigue were evaluated in the dominant quadricep muscle group. During the control test, exercise performance was limited to that of isokinetic evaluation. The order of the experimental and control tests were randomly assigned. Postexercise blood lactate levels prior to the isokinetic muscle test were 9.2 and 9.1 mM during the active and passive recovery conditions respectively. Blood lactate concentration during the control test was .4 mM prior to the isokinetic muscle test. The rate of blood lactate disappearance was significantly greater during active recovery (3.5 mM) when compared with passive recovery (7.2 mM). Blood lactate concentration during the control test was significantly lower (.4 mM) in comparison to both active and passive lactate concentrations prior to the isokinetic muscle test. Despite significant differences in blood lactate between active and passive recovery conditions, there was no difference in isokinetic measures of maximal strength, work output and muscle fatigue between recovery modes. Further indication that lactate is unrelated to muscle function was the nonsignificant finding in muscle function between the control and experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymorphic phase behavior of lysophosphatidylethanolamine dispersions. A thermodynamic and spectroscopic characterization

We have investigated the phase behavior of aqueous dispersions of a series of synthetic lysophosphatidylethanolamines as a function of the acyl chain length. Lysophosphatidylethanolamines exhibit phase polymorphism encompassing a well-ordered crystalline phase which may arise either from a metastable interdigitated lamellar gel phase or a metastable micellar phase. The time course of interconversion between these various phases have been outlined by observing the low temperature incubation time dependence of the calorimetric thermograms. We have determined differences in structure of these phases by Raman spectroscopy and 31P nuclear magnetic resonance spectroscopy. It appears that a principal contribution to this polymorphic phase behavior lies in the nature of headgroup hydration and headgroup-headgroup interactions.

Effects of dietary fish oil or pectin on blood pressure and lipid metabolism in the DOCA-salt hypertensive rat

This study investigated the effects of diets containing fish oil or pectin on blood pressure and lipid metabolism in the deoxycorticosterone acetate (DOCA)-salt hypertensive rat. Three groups (8 rats/group) of unilaterally nephrectomized rats were fed for 21 d one of three purified diets: a) 8% fish oil + 2% safflower oil + 5% alpha cellulose (fish oil diet), b) 10% safflower oil + 5% pectin (pectin diet), or c) 10% safflower oil + 5% alpha cellulose (control diet). Each of the diets contained 6% NaCl and all rats received DOCA (30 mg/kg body wt, subcutaneously) twice weekly. Systolic blood pressure of rats fed fish oil was significantly lower (P less than 0.05) than that of rats fed the control diet; there was no significant difference between the pectin and control groups. Plasma renin activity and net sodium and potassium balances were similar among the three groups. Plasma total cholesterol, LDL cholesterol and HDL cholesterol were significantly lower (P less than 0.05) in the group fed the fish oil diet than in the group fed the control diet. Total, LDL and HDL cholesterol did not differ between rats fed the pectin and rats fed the control diet. Plasma triglyceride concentration did not differ among the three groups. Thus, dietary fish oil attenuated the development of DOCA-salt hypertension, unrelated to alterations of net sodium balance. Fish oil feeding also lowered total, LDL and HDL cholesterol, but did not alter the HDL/LDL ratio. In contrast, dietary pectin exerted no effect on blood pressure or lipid metabolism.

Emotional closeness and physical distance between friends: implications for elderly women living in age-segregated and age-integrated settings

The author discusses the need for a better theoretical understanding of friendship in order for its role in the lives of elderly people to be understood. The applicability to friendship of Simmel's approach to the study of social relationships is outlined. From this perspective, types of friendship are determined by the physical distance separating friends and the emotional closeness bringing them together. The data consist of seventy in-depth interviews of senior, unmarried women in a middle-class community bordering on Chicago. Qualitative data are reported to support quantitative analyses. There were positive relationships between emotional closeness and physical distance, duration and emotional closeness, and frequency of interaction and proximity. The author describes the implications for elderly women of the tendency for their close, old friends to be physically separated from them and their neighbors to be casual friends, but constant companions. The author discusses the effects of the age-density of residential context and life history on the types of friends the women had.

Reduced plasma kininogen concentration during sickle cell crisis

Eight patients with sickle cell anemia (SS hemoglobin) were found to have decreased plasma levels of kininogen compared to normal control subjects. The kininogen level of the patients with sickle cell anemia was decreased further during sickle cell crises. The results suggest that components of the kinin system are profoundly affected in patients with sickle cell anemia, and during crises may play a role in the clinical presentation of patients.

Analysis of mortality from nephritis and nephrosis among nickel-cadmium battery workers

Mortality from nephritis and nephrosis (and other diseases of the genitourinary system) experienced by a study cohort of 3,025 nickel-cadmium battery workers was investigated. Observed (O) numbers of deaths from these diseases for the period 1946 through 1981 were compared with those that might be expected (E) to occur on the basis of rates of mortality for the general population of England and Wales (nephritis and nephrosis, International Classification of Diseases, eighth revision [ICD 8th] Code No. 580-584; E = 5.49, O = 10: all disease of the genitourinary system (noncancers), ICD 8th 580-629; E = 11.50, O = 17). These differences were not statistically significant at the 5% level. When the estimated cadmium exposures of those who died from these causes were compared with those of all matching survivors using the method of regression models in life-tables, no statistically significant association was found between occupational exposure to cadmium and mortality from these diseases. A separate analysis was made of the mortality experience of 39 workers with cadmium nephropathy.

Studies of the kallikrein-kinin system in patients with sickle cell anemia

Eight patients with sickle cell anemia (SS hemoglobin) were found to have decreased plasma levels of prekallikrein compared to normal control subjects or patients with other types of anemia. The prekallikrein levels in the patients with sickle cell anemia were found to decrease further during a sickle cell crisis. These results suggest that components of the kallikrein-kinin system are profoundly affected in patients with sickle cell anemia, and during crises may play a role in the clinical presentation of patients.

Inhibition of canine lung angiotensin converting enzyme by substance P

We have studied inhibition of purified canine angiotensin converting enzyme by substance P and its nonapeptide derivative using Hip-His-Leu as the substrate. Kinetic studies indicated that both substance P and its nonapeptide derivative inhibited the hydrolysis of Hip-His-Leu at different concentrations. The mode of inhibition was competitive with a Ki of 1.15 microM for substance P. These results indicate that substance P is a potent inhibitor of angiotensin converting enzyme in vitro.

Plasma pharmacokinetics of intravenously administered atropine in normal human subjects

The pharmacokinetics of atropine (dl-hyoscyamine) was studied in six normal volunteers following a single 1-mg intravenous dose of atropine. Atropine plasma levels were collected for 24 hours and analyzed by radioimmunoassay. Pulse rates were monitored and compared with predose values in each subject. Atropine plasma concentrations were fitted by least-squares regression analysis. The observed maximal increase in pulse rate, at 12 to 16 minutes after the dose, correlated with the maximum predicted tissue levels of atropine based on the computer fit of the plasma atropine concentration-time data. No correlation between the time of maximum response and atropine plasma concentrations was observed. The average half-life of atropine was 4.125 hours. This data may be used to design a multiple-dosing regimen for intravenous atropine in patients.

Infrared spectroscopic study of the secondary structure of melittin in water, 2-chloroethanol, and phospholipid bilayer dispersions

The conformations of melittin, an amphipathic polypeptide consisting of 26 amino acid residues, and its hydrophobic (residues 1--19) and hydrophilic (residues 20--26) fragments were examined in various solvent systems, including H2O, 2H2O, 2-chloroethanol, and 1,2-dimyristoylphosphatidylcholine (DMPC) multilayers, by infrared spectroscopy. Water and 2-chloroethanol were used as reference solvents for characterizing the amide I and II vibrational frequencies of the polypeptide in systems reflecting unordered, beta-structure, or alpha-helical forms. In DMPC bilayer assemblies both melittin and its hydrophobic fragment F1 exhibit alpha-helical conformations. In contrast, infrared spectra for the hydrophilic F2 fragment are suggestive of a beta conformation with perhaps spectral contributions from random-coil configurations. The alpha-helical conformation of intact melittin in DMPC multilayer dispersions remains unchanged as the bilayer passes from the gel to liquid-crystalline state. For melittin-water solutions the infrared spectra monitor changes in population of specific conformations as the temperature is varied. Thus, for melittin concentrations in which tetramers are dominant high temperatures (31 degrees C) favor the alpha-helical form, while low temperatures (8 degrees C) lead to populations of both beta and alpha-helical structures. At lower melittin concentrations for which monomers persist, high temperatures favor an unordered polypeptide form, while low temperatures induce an alpha-helical conformation. Although peak-height intensity ratios AII/AI for the amide I and II regions are difficult to interpret rigorously, values of this parameter for aqueous solutions of melittin suggest a sensitivity to structural changes involving the aggregation properties of the polypeptide.

Structural reorganizations in lipid bilayer systems: effect of hydration and sterol addition on Raman spectra of dipalmitoylphosphatidylcholine multilayers

Vibrational Raman spectroscopy was used in investigate the conformational behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers perturbed by cholesterol and water, two membrane components whose lipid interactions involve different regions of the bilayer matrix. Upon the addition of cholesterol, an intrinsic membrane constituent, to an anhydrous bilayer in concentrations varying from 7 to 30 mol %, modifications in lateral chain interactions were observed by monitoring spectral changes in the methylene C-H stretching and the CH2 deformation regions. The perturbation in the 1460-cm-1 region was not spectroscopically observed until after the addition of 7 mol % of the sterol. Although chain-chain interactions are altered, no additional trans/gauche isomerization is developed along the hydrocarbon chains. Water, a peripheral bilayer component, was added to the multilayer assembly in the hydration range of 0.3 to 4 molecules of water per lipid molecule. Vibrational spectra characteristic of motions in the head-group, interfacial, and acyl chain regions of the lipid bilayer were observed. These data indicate that hydration confers a mobility to the head-group, glycerol, and carbonyl moieties. Shifts in the CN symmetric and PO2-antisymmetric stretching modes, occurring on the addition of approximately four molecules of water, indicate a conformational rearrangement within the polar head group. After approximately four molecules of water are added to the DPPC system, the spectral features of the gel system [70% (w/w) water] indicate that not further head-group changes nor increases in either acyl chain trans/gauche or lattice disorder arise on further hydration.

Cadmium-induced osteomalacia

The detailed study of a battery plate maker, who had worked with cadmium for 36 years, showed that proteinuria, typical of renal tubular dysfunction, had been observed for 25 years and during the last 12 years of his life the patient had suffered increasing disability from gross bone disease. Several bone biopsies and detailed metabolic studies showed typical severe osteomalacia, which responded well initially to calcium and vitamin D treatment. Examination of the liver both in life and after death showed a gross excess of cadmium. This was also found in the kidneys after death. Previously unreported changes were present in the bones, especially the lumbar vertebrae which were probably more the result of gross bone deformity than cadmium deposition. The mechanism of development of the severe acquired Fanconi syndrome was thought to be a combination of dietary calcium and vitamin D deficiency and impaired calcium absorption from abnormal vitamin D synthesis, related to the cadmium deposition in the renal tubules, which also caused the defect in renal tubular reabsorption.

Isolation and identification of phospholipids of bovine rhodopsin

Phospholipids present in digitonin solutions of bovine rhodopsin have been identified and assayed. Digitonin interferes with extraction of lipids by the usual methods; digitonin was therefore removed from the preparation as an ergosterol digitonide, soluble in absolute ethanol but precipitated in 80% ethanol. The supernatant 80% ethanol contained one portion of the phospholipid, mainly choline and ethanolamine phosphoglycerides with traces of serine phosphoglyceride and sphingomyelin. The rhodopsin residue (free from digitonin) was extracted with chloroform-methanol 2:1; this extract contained the rest of the phospholipid, which consisted only of choline and ethanolamine phosphoglycerides. Plasmalogens were not found, but could have decomposed during the procedures.

Effect of light on extraction of lipid from retinal rods

Chloroform-methanol 2:1 removes a significantly greater quantity of lipid from bleached bovine retinal rods than from a dark-adapted counterpart. The extracts contain phosphatidyl serine, phosphatidyl choline, phosphatidyl ethanolamine, sphingomyelin, and an unknown substance which, it is proposed, may be a combination of phospholipid and retinaldehyde. The difference between extracts of light-and dark-adapted rods is quantitative rather than qualitative. The data tend to confirm a model of rhodopsin suggested by Kropf and Hubbard in which isomerization of the retinaldehyde chromophore causes its displacement and opens a path to the interior of the molecule.