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Biomedical subjects

R G Snyder

Publications and source records attributed to R G Snyder.

At least 19 recordsLinked to original sources
PubMed1996

IR spectroscopic study of the structure and phase behavior of long-chain diacylphosphatidylcholines in the gel state.

Fully hydrated dispersions of simple linear saturated diacylphosphatidylcholines with even-numbered acyl chains of lengths from 18 to 24 carbons can exist in a low-temperature, highly ordered, orthorhombic phase (G(o)) that differs from the L beta phase (Gd) normally found for shorter chains. The temperature behavior of these dispersions has been studied by infrared spectroscopy. Chain packing in the G(o) phase was found to be nearly identical to that of the orthorhombic phase of crystalline n-alkanes. With increasing temperature, the G(o) phase undergoes a transition to Gd at approximately 45 degrees C below Tm. This transition occurs at a higher temperature and becomes sharper with increasing chain length. Chain packing in the Gd phase was found to be disordered in a way that can be expressed in terms of a distribution of subcell setting angles. The Gd phase converts to a phase (Gh) with hexagonal-like chain packing at temperatures below Tm. The results support and extend those of a recent x-ray diffraction study of the 24-carbon diacyclphosphatidylcholine gel.

Calorimetry, Differential Scanning↗
PubMed1995

IR spectroscopic determination of gel state miscibility in long-chain phosphatidylcholine mixtures.

We report on the gel-state microaggregation in binary mixtures of diacylphosphatidylcholines over temperatures ranging from -19 degrees C to near the gel-to-liquid crystal transition. Microaggregates with lateral dimensions in the range 1-100 chains were detected and measured with an isotope infrared method that relates the splitting or the shape of the methylene scissors band to aggregate size. Measurements were made on fully hydrated dispersions of diC18DPC/diC20HPC, diC18DPC/diC22HPC, and diC18DPC/diC24HPC at molar ratios of 4:1. Low levels of aggregation were determined with reference to the spectrum of the random mixture diC18DPC/diC18HPC. For diC18DPC/diC20HPC at -19 degrees C, which previous calorimetric measurements have indicated is a nearly ideal, we found about 4% of the minority component chains to be involved in aggregates. For diC18DPC/diC22HPC, the value increased to about 11%. DiC18DPC/diC24HPC was found to be highly fractionated, in agreement with the earlier studies. The unit subcell, which defines the type of acyl-chain packing, was determined for the components of the mixtures. The temperature behavior of the phases and the temperatures at which the minority component domains undergo dissolution were determined.

Biophysical Phenomena↗
PubMed1995

Biomechanics of skull fracture.

This study was conducted to determine the biomechanics of the human head under quasistatic and dynamic loads. Twelve unembalmed intact human cadaver heads were tested to failure using an electrohydraulic testing device. Quasistatic loading was done at a rate of 2.5 mm/s. Impact loading tests were conducted at a rate of 7.1 to 8.0 m/s. Vertex, parietal, temporal, frontal, and occipital regions were selected as the loading sites. Pathological alterations were determined by pretest and posttest radiography, close-up computed tomography (CT) images, macroscopic evaluation, and defleshing techniques. Biomechanical force-deflection response, stiffness, and energy-absorbing characteristics were obtained. Results indicated the skull to have nonlinear structural response. The failure loads, deflections, stiffness, and energies ranged from 4.5 to 14.1 kN, 3.4 to 16.6 mm, 467 to 5867 N/mm, and 14.1 to 68.5 J, respectively. The overall mean values of these parameters for quasistatic and dynamic loads were 6.4 kN (+/- 1.1), 12.0 mm (+/- 1.6), 812 N/mm (+/- 139), 33.5 J (+/- 8.5), and 11.9 kN (+/-0.9), 5.8 mm (+/- 1.0), 4023 N/mm (+/- 541), 28.0 J (+/- 5.1), respectively. It should be emphasized that these values do not account for the individual variations in the anatomical locations on the cranium of the specimens. While the X-rays and CT scans identified the fracture, the precise direction and location of the impact on the skull were not apparent in these images. Fracture widths were consistently wider at sites remote from the loading region. Consequently, based on retrospective images, it may not be appropriate to extrapolate the anatomical region that sustained the impact forces. The quantified biomechanical response parameters will assist in the development and validation of finite element models of head injury.

Aged↗
PubMed1993

Analysis of the delocalized Raman modes of conformationally disordered polypeptides.

Bands associated with delocalized vibrational modes were identified in the isotropic Raman spectra of a series of polyglycine oligomers in aqueous solution as zwitterions and as cations. The dependence of these bands on conformational disorder and chain length was determined. The observed dependence is closely mimicked in spectra calculated for a series of corresponding model polypeptides. The simulated spectra were calculated in a skeletal approximation for ensembles of conformationally disordered chains. As the chain length of the conformationally disordered polypeptides increases, the observed isotropic spectra rapidly approach the spectrum of the infinitely long disordered chain. Convergence is nearly complete at the tripeptide for both the zwitterion and the cation. The stimulated spectra behave in essentially the same way. Convergence to the spectrum of the infinitely long chain is much more rapid for the conformationally disordered polyglycines than for the ordered polyglycines because of the mode localization that results from disorder. In the low-frequency region the bands in the calculated spectra have frequencies that are systematically dependent on chain length. These bands are related to the longitudinal acoustic modes of the ordered chain.

Biophysical Phenomena↗
PubMed1992

Intracoronary PGE2 and veratrine inhibits renin release in conscious dogs via chemosensitive ventricular afferents.

1. Prostaglandins (PG) and veratrum alkaloids stimulate ventricular sensory receptors with non-myelinated vagal afferents and mediate inhibitory circulatory responses. 2. The present study in conscious instrumented dogs was carried out to determine the effects of intracoronary artery infusions of veratrine (Ver-IC) and PGE2 (PGE2-IC) on plasma renin activity (PRA). 3. A 15-20 mmHg decrease in arterial pressure was produced during Ver-IC (0.2-0.8 micrograms/kg per min) and PGE2-IC (10-50 ng/kg per min), but there was no change in PRA or heart rate. 4. In contrast, significant increases in PRA (+3.51 +/- 0.37 ng angiotensin I/mL per h; P less than 0.01) and heart rate (+38.5 +/- 6.2 beats/min; P less than 0.001) were elicited in response to a 15-20 mmHg decrease in arterial pressure produced by intravenous infusions of nitroprusside. 5. Pharmacological blockade of afferent fibres in the pericoronary region of the left main coronary artery during Ver-IC resulted in significant hypotension-induced increases in PRA (P less than 0.001) and heart rate (P less than 0.001), thus removing the inhibitory influence of chemosensitive ventricular afferents. 6. Therefore, intracoronary veratrum alkaloids and prostaglandins inhibit hypotension-induced increases in PRA and heart rate in the conscious dog. This is mediated by chemosensitive receptors located in the left ventricular myocardium along with afferent nerves in the pericoronary region and cervical vagi.

Animals↗
PubMed1989

Pentagastrin induction of spermine/spermidine N1-acetyltransferase and mucosal polyamines.

The trophic response of the gastrointestinal mucosa to treatment with the hormone gastrin includes a polyamine-dependent step. Because gastrin does not induce ornithine decarboxylase, experiments were designed to determine whether pentagastrin induced the polyamine interconverting enzyme, spermine/spermidine N1-acetyltransferase (SAT). Eight hours after intraperitoneal treatment of rats with either spermidine (0.8 mmol/kg) or pentagastrin (250 micrograms/kg) oxyntic gland mucosal SAT activity was increased from roughly 400 to 800 pmol [14C]acetate.mg protein-1.h-1. In contrast, colonic mucosa was not sensitive to pentagastrin even though spermidine treatment induced nearly a 400% increase in SAT activity. Measurement of both oxyntic gland and colonic mucosal polyamine concentrations showed that by 16 h after pentagastrin (250 micrograms/kg ip) putrescine, acetylspermidine, and spermidine levels all were increased to a level approximately 200% of that observed in NaCl-treated rats. By 24 h mucosal polyamine content of pentagastrin-treated rats was not different from control. Essentially the same results were found in animals treated with difluoromethylornithine, thus demonstrating that the increase in mucosal polyamine concentration was not related to the induction of ornithine decarboxylase. The results of these experiments demonstrate that unlike most hormones, the hormone gastrin induces the polyamine converting enzyme, SAT, rather than ornithine decarboxylase during stimulation of polyamine-dependent cell growth and/or division.

Acetyltransferases↗
PubMed1988

Effects of air quality on foliar injury, growth, yield, and quality of muskmelon.

An evaluation of the effects of ambient ozone (O3) on muskmelon was conducted with the use of open-top chambers (OTCs). 'Superstar' muskmelons grown in charcoal-filtered (CF) chambers compared to those grown in nonfiltered (NF) chambers showed significant differences in the severity of visible foliar O3 injury. Furthermore, plants grown in NF conditions had significantly less (21.3%) marketable fruit weight and fewer (20.9%) marketable fruit number than those from CF chambers. No differences were found in early biomass production, leaf area, or number of nodes after 3 weeks of exposure to treatment conditions. Ambient O3 did not affect soluble solids content of mature fresh fruit nor foliage fresh weight at final harvest. Results indicate that ambient concentrations of O3 in southwestern Indiana caused significant foliar injury and yield loss to muskmelons.

Journal Article↗
PubMed1980

Effects of chain packing and chain mobility on the Raman spectra of biomembranes.

The degree of lateral crystal-like order between hydrocarbon chains in biomembrane systems can be estimated from Raman measurements in the C-H stretching region. Observations of the temperature dependence of the Raman spectra of crystalline n-C16H34 and the urea clathrate of n-C16H34 have enabled us to separate to some extent the overlapping effects of chain packing and chain mobility, effects that are normally not distinguished in considering lateral order. The mobility is associated with the freedom of an extended chain to rotate and twist about its long axis. A high degree of such motion must be ascribed to n-C16H34 in a urea clathrate in order to explain the unusual temperature behavior observed for Raman bands at 2885 and 1174 cm-1. Comparison of the temperature behavior of the Raman spectra of the clathrate with that of crystalline n-C16H34 permits the effects due to packing and to mobility to be distinguished. The same effects can be expected to be present in the Raman spectra of biomembranes.

Alkanes↗
PubMed1975

Are 1974-1975 automotive belt systems hazardous to children?

The 1974 and early-1975 model automobiles are equipped with belt interlock systems that require front outboard seat occupants who weigh more than 21.5 kg (47.3 lb) to wear threepoint lap and diagonal upper-torso belts (or wear the lap belt and position upper-torso belt behind them), assuming that the interlock has not been circumvented. Recent legislation has eliminated the interlock requirement, but new models are still likely to be fitted with three-point restraints for the front outboard seating positions. These restraint systems were designed and tested for adult use. Thus, based on the different structure of a younger child and the fact that there is a wide variation of belt orientation, child size, and seating environments, there is legitimate concern that the upper diagonal belt might contribute to injury of the child under certain impact conditions.

Adolescent↗
PubMed1975

A rapid technique for preparation of human fetal and adult skeletal material.

The techniques described above have been found to provide a rapid method of human skeletal preparation, with advantages of speed and applicability to fresh, fixed, or partially decomposed skeletal materials. While other techniques which can be used include the traditional use of Dermestidae beetle colonies, a five-step anatomical procedure, and other combinations of chemical solvents, the antiformin technique appears to have advantages useful to those involved in forensic medicine.

Adult↗