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Biomedical subjects

N B Smith

Publications and source records attributed to N B Smith.

52 records · Page 3Linked to original sources
PubMed1982

Determination of cholesteryl esters and of cholesteryl and epicholesteryl silyl ethers by capillary gas chromatography.

The capillary gas chromatography of cholesteryl esters after splitless injection into a 25-m, OV-1-coated, fused silica WCOT column and a 7-m Silar 10C-coated glass WCOT column is reported. The nonpolar OV-1 column separated the cholesteryl esters principally on the basis of carbon number, but separation of the saturated esters from the unsaturated esters was also achieved. The polar Silar 10C column separated the esters mainly according to the degree of unsaturation. Thus, the 2 column types complement each other in the analysis of nanogram quantities of cholesteryl esters from small samples, such as those from plasma or single arterial atherosclerosis lesions. This technique therefore obviates some of the difficulties of analyzing such cholesteryl ester samples in the form of methyl esters (incomplete transmethylation, and contamination by solvent impurities and/or plasticizer esters). Both columns were also found to be useful for the separation and quantitation of the t-BDMS ethers of cholesterol and epicholesterol in mixtures containing various proportions of these epimers.

Cholesterol↗
PubMed1981

Exchange of phosphatidylcholine between rabbit erythrocytes and plasma in vivo.

Phosphatidylcholine exchange between rabbit erythrocytes and plasma was studied in vivo. The erythrocyte phosphatidylcholine was labeled by exchange in vivo with [32P] phosphatidylcholine and in vitro by acylation with [3H] 16:0 and [14C] 18:2. The erythrocytes were then injected into rabbits and the loss of labeled phosphatidylcholine from the cells by exchange was followed. The rate constants for the exchange of [32P]-, [3H] 16:0-, and [14C] 18:2-phosphatidylcholine were .013 +/- .0010, .0093 +/- .0014 and .0074 +/- .0013 h-1, and the exchange rates of the labels relative to that of [32P] were 1.0, 0.71 +/- .16, and 0.56 +/- .14, respectively. These results confirm our earlier in vitro findings and represent the first in vivo demonstration of the dependency of the exchange rate of erythrocyte phosphatdylcholines on their metabolic prehistory.

Animals↗
PubMed1980

Relationship between the cholesteryl esters and free cholesterol of individual atherosclerotic lesions and lesion size in aortas of rabbits on atherogenic and regression diets.

A study was made on the cholesterol lipids and DNA in lesions of aortas of rabbits either fed continuously on a cholesterol-rich diet or fed the cholesterol-rich diet for 6 weeks followed by a chow diet for up to 22 weeks. The DNA content of the aortic intimal-medial lesion samples was proportional to the surface area of these samples. The content of cholesteryl ester and unesterified cholesterol of the aortic lesions was compared with lesion area, lesion DNA and the topographical location on the thoracic and upper abdominal aorta luminal surface. The largest 80% of the lesions in an aorta contained a disproportionately large amount of cholesteryl ester compared to the smallest 20% of the lesions. The lesion content of free cholesterol compared to lesion area followed a nearly linear relationship. Similarly, cholesteryl ester content was non-linearly related to lesion DNA content but free cholesterol content was nearly proportionally related to DNA content. The non-linear relationships of cholesteryl ester content to lesion size and DNA content may be associated with a non-linear relationship between lipid inclusion volume and lesion size. The linearity observed for free cholesterol content as a function of lesion size may be due to a linear relationship between lipid inclusion surface area and lesion size. Neither diet nor the topographical location of lesions appeared to be important factors in affecting the cholesterol lipid content of lesions. Lesions became more irregular in shape as they grew larger.

Animals↗
PubMed1980

Stereochemical substrate requirements of lecithin:cholesterol acyltransferase and its inhibition by enantiomeric lysolecithins.

The suitability of 1-sn-phosphorylcholine- and 2-sn-phosphorylcholine-diacylglycerols as substrates for lecithin:cholesterol acyltransferase (LCAT) was assayed under standardized conditions using sonicated liposomes of radioactive phospholipids. The results were compared with those obtained for the corresponding molecular species of the natural 3-sn-phosphorylcholinediacylglycerol. It was found that with the 2-sn-phosphorylcholinediacylglycerol, LCAT had only 16% of the activity that it showed for 3-sn-phosphorylcholinediacylglycerol, while its activity with 1-sn-phosphorylcholinediacyglycerol as the substrate was not significant. It is concluded that LCAT possesses highly specific steric and positional requirements for its phosphatidylcholine substrates and that, like phospholipase A2, it has a significant activity with the 2-sn-phosphorylcholinedicacylglycerol. It wa also shown that the activity of LCAT is inhibited by both enantiomers of lysophosphatidylcholine as well as Triton X-100. In all instances the inhibition was reversed by the addition of lipid-free albumin. It is concluded, therefore, that the inhibition of LCAT by lysophosphatidylcholine is a detergent rather than an end-product inhibition phenomenon.

Glycerylphosphorylcholine↗
PubMed1979

Chemical defense of crinoids by polyketide sulphates.

The range of (presumed) polyketide constituents in comatalid crinoids has been extended to include bianthronyls, meso-naphthodianthrones and sulphate esters of various of the polyketides. Several species of fish are deterred from eating food by the inclusion in it of these sulphates at the concentration found in crinoids. Sodium 2-hydroxy-anthraquinone sulphate and anthraquinone-2-suphonate were also active as antifeedants for the species tested.

Animals↗
PubMed1978

Synthesis of 1-sn-lysophosphatidylcholine and mixed acid 1-sn-phosphatidylcholine.

An investigation of the biochemical effects of L-lysophosphatidylcholine (1-acyl-sn-glycerol-3-phosphorylcholine) requires as a control for its detergent action the metabolically inert, unnatural enantiomer, D-lysophosphatidylcholine (3-acyl-sn-glycerol-1-phosphorylcholine). The latter can be easily prepared in milligram quantities from the commercially available DL-phosphatidylcholine. For this purpose rac-1,2-dipalmitoyl-sn-glycerol-3-phosphorylcholine is solubilized with the aid of one-half its weight of taurocholate and hydrolyzed with phospholipase A2 to completion and the intact residual 2,3-dipalmitoyl-sn-glycerol-1-phosphorylcholine recovered by chromatography. The pure D-phosphatidylcholine is then subjected to methanolysis in the presence of octylamine and the product isomerized with glacial acetic acid. The 3-palmitoyl-sn-glycerol-1-phosphorylcholine thus obtained is chromatographically pure, possesses correct optical rotation and NMR spectrum, and is resistant to hydrolysis by phospholipase A2 following reacylation to the diacylphosphatide. Acylation of the 1-sn-lysophosphatide provides a convenient method for preparation of mixed acid 1-sn-phosphatidylcholines which are not otherwise available.

Isomerism↗
PubMedDate not supplied

Control system for an MRI compatible intracavitary ultrasound array for thermal treatment of prostate disease.

A 16-channel ultrasound intracavitary array is currently being used in a clinical setting for localized hyperthermia treatment of prostate tumours. Currently, the individual power to each array element is adjusted based on the clinician's judgement of the temperature measured at the locations of invasive thermocouple probes. MRI-derived temperature measurements may be useful for a feedback control system that non-invasively regulates the temperature distribution by adjusting the power to the elements of the array. MRI has been shown to provide accurate, high resolution, non-invasive thermometry. A proportional-plus-integral, single-input, single-output controller was designed to evaluate the feasibility of MRI-derived temperature feedback with this applicator. Input parameters for the controller were determined by modelling the tissue response to the heating from the array. Ex vivo and in vivo experiments evaluated the ability of the MRI-based temperature feedback control system to achieve and maintain a target temperature for a sustained period similar to that of a clinical hyperthermia treatment. With the controller set to a reference temperature of 43 degrees C and a rise time of 6 min, the temperatures within the ex vivo tissue (n = 6) were 43.1 +/- 0.3 degrees C after reaching the reference temperature and had a rise time of 9.5 +/- 0.3 min. In vivo results using rabbit thigh muscle (n = 7) showed that the steady state temperatures were within +/- 1 degree C of their target temperatures. These results demonstrated the feasibility of a temperature feedback for controlling the heating from an intracavitary transrectal array based on temperature information from MR images.

Animals↗
PubMedDate not supplied

Simple sensitive solid-phase extraction of paraquat from plasma using cyanopropyl columns.

We report an inexpensive, sensitive paraquat quantitation method which is simple to perform. First, 5 mL of blanks, standards, or patient plasma are applied to 1-mL cyanopropyl extraction columns equipped with 15-mL reservoirs. The samples are drawn through the columns under vacuum, followed by a rinse with 15-20 mL of 0.1M NH4OH. Paraquat is eluted with 0.8 mL 0.1M HCl, which is then neutralized with 25 microL concentrated NH4OH. Sodium dithionite reagent (0.23M in 4M NaOH) is added (100 microL) and the color produced is measured by absorbance difference (A395-A460). The assay is linear up to at least 4.35 microM paraquat. The lower limit of quantitation is 0.23 microM. Lipemic and icteric sera do not affect the method, but easily visible hemolysis elevates the concentrations measured by up to 0.7 microM, independent of paraquat concentration. Equimolar amounts of diquat with paraquat, at paraquat concentrations from 0.4 to 4.0 microM, elevate apparent paraquat concentrations by 0.08-0.28 microM. At 0.632, 1.92, and 4.06 microM paraquat, within-run coefficients of variation (CVs) were 6.27, 7.23, and 2.14%, and between-run CVs were 6.82, 8.42, and 4.43%, respectively.

Colorimetry↗
PubMedDate not supplied

Automated identification by computer of the mass spectra of drugs in urine or serum extracts.

Gas chromatography/mass spectrometry (GC/MS) is the method of choice for confirming the presence of drugs tentatively identified in urine or serum by thin-layer chromatography, gas chromatography, or immunoassay. One of the most widely used GC/MS systems is the Hewlett-Packard (HP) Model 5970 mass selective detector equipped with a work station programmed in Pascal. Searching of mass spectra after a GC/MS run must be done manually, and this can take hours, especially when there are many peaks in a chromatogram to check. I have developed software that allows the unattended searching of all peaks in a run, using a forward search algorithm with a custom-made drug library developed over a period of 5 years, and a reverse search with a 1600+ drug library from HP or another in-house drug library. Using these libraries with the two algorithms maximizes the chances of finding a drug peak and identifying it correctly. Individual searches take about 5 seconds each. Overall search time of nearly 200 mass spectra per run takes about 40 minutes, including printing time. This software has proven to be both labor saving and effective in positively identifying drugs.

Electronic Data Processing↗