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M Bouchard

Publications and source records attributed to M Bouchard.

At least 37 records · Page 2Linked to original sources
PubMed1999

The toxicokinetics of pyrene and its metabolites in rats.

Five experiments were conducted in male Sprague-Dawley rats regarding the kinetic of urinary excretion of 1-hydroxypyrene (1-OHP) following i.v., oral and dermal exposure to 0.5-50 micromol/kg pyrene either as a single substance or as mixture of various polycyclic aromatic hydrocarbons (PAH). Frequent urine collections over 48 h after exposure and a tissue versus time distribution experiment using [14C]pyrene allowed to define the kinetic profile of both pyrene and 1-OHP. For all exposure routes, there is a linear relationship over two orders of magnitude between the dose of pyrene and the urinary excretion of 1-OHP. Differences in biliary/urinary 1-OHP excretion ratio in canulated rats (3) versus faecal/urinary 1-OHP excretion ratio in non-canulated rats (0.6) indicate major enterohepatic recirculation of the metabolite. Half-lives of both pyrene and 1-OHP in all measured tissues were all comprised between 3.1 and 5.4 h, and 5.2-6.7 h, respectively, so that no long term accumulation would be predicted from these values for any tissue. Binary and ternary mixtures involving naphthalene and benzo(a)pyrene in addition to pyrene has no influence on the urinary excretion profile of 1-OHP. All these observations led to the proposal of a dynamic compartment model of pyrene and metabolite flows indicating that following rapid initial distribution to fatty tissues, pyrene is rapidly biotransformed into various metabolites and undergoes major enterohepatic recycling. Part of the initially formed and part of the recirculated 1-OHP eventually undergoes urinary excretion such that close to 60% of pyrene is eliminated as metabolites in urine by 24 h after injection while 20% is excreted in the faeces over the same period.

Administration, Oral↗
PubMed1999

Orthopedic management in autosomal recessive spastic ataxia of Charlevoix-Saguenay.

OBJECTIVE: To review the orthopedic management of choice in patients having autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). DESIGN: A retrospective study from April 1978 to April 1997. SETTING: Centre hospitalier de la Sagamie, Chicoutimi, Que. PATIENTS: A review of the records of patients having ARSACS who were identified in the registry of the Neuromuscular Diseases Clinic at the Centre hospitalier de la Sagamie revealed 26 patients who received surgical orthopedic treatment. Initially, the patients were offered conservative treatment, which consisted of physiotherapy sessions, the wearing of an ankle-foot orthosis or serial casting. When this was unsuccessful, foot surgery was considered. RESULTS: During the study period, 49 orthopedic procedures were done, including 24 triple arthrodeses; of these, 9 were combined with lengthening of the Achilles tendon. Most triple arthrodeses were done in patients between the ages of 30 and 49 years. The surgical options evolved during the study from Lambrinudi arthrodesis through arthrodesis of the ankle to triple arthrodesis with lengthening of the Achilles tendon. CONCLUSIONS: As a complement to conservative treatment, surgery has a place in the care of patients with ARSACS. Clinically, the most effective surgical procedures are triple arthrodesis with percutaneous lengthening of the Achilles tendon and adductor and psoas tenotomies combined with neurectomy of the obturator nerve for perineal hygiene.

Achilles Tendon↗
PubMed1998

Comparison between the dynamics of lipid/gramicidin A systems in the lamellar and hexagonal phases: a solid-state 13C NMR study.

We have investigated the effect of gramicidin A on the dynamics of two model membranes: dimyristoylphosphatidylcholine (DMPC) in the lamellar phase at a lipid-to-peptide molar ratio of 10:1 and dioleoylphosphatidylcholine (DOPC) in the hexagonal HII phase at a lipid-to-peptide molar ratio of 5:1. Natural abundance 13C nuclear magnetic resonance (NMR) spectroscopy was used in combination with magic angle spinning to increase the spectral resolution, therefore allowing the different regions of the lipid bilayers to be investigated from the same spectra. 31P NMR was also used to detect and confirm the formation of the DOPC HII phase in the presence of gramicidin A. In order to examine the effect of gramicidin A on both the fast and slow motions of DMPC and DOPC, the 1H spin-lattice relaxation times in the laboratory frame (HT1) as well as the 1H spin-lattice relaxation times in the rotating frame (HT1rho) were calculated for each resolved protonated lipid resonance in the 13C spectra. For both DMPC and DOPC, we found that the presence of gramicidin A does not significantly affect the fast motions of the lipid acyl chains but increases slightly the fast motions of the polar head group. However, the HT1rho are significantly decreased, this effect being more pronounced for DOPC most likely due to a decrease in the rate of the lipid lateral diffusion.

Carbon Isotopes↗
PubMed1998

Urinary and biliary excretion kinetics of 1-hydroxypyrene following intravenous and oral administration of pyrene in rats.

The urinary and biliary excretion kinetics of 1-hydroxypyrene (1-OHP) were compared in male Sprague-Dawley rats exposed intravenously and orally to 1.5, 5, 15, 50 and 100 micromol/kg pyrene. Urine and bile samples were collected at 6-h intervals for up to 24 h. Results showed that the kinetics of 1-OHP were similar for both biliary and urinary excretion whatever the administered dose or exposure route. Furthermore, the time course of 1-OHP excretion in either bile or urine following intravenous dosing resembled that observed after oral administration. In addition, the exposure route and dose had no significant effect on the fraction of dose recovered in urine and bile as 1-OHP after 6, 12, 18 and 24 h post-dosing. Following intravenous injection of 1.5, 5, 15, 50 and 100 micromol/kg pyrene, the mean cumulative percent of dose excreted as 1-OHP in urine over 24 h ranged from 1.7 to 3.2%, while biliary values ranged from 6.5 to 9.5%. Correspondingly, after oral administration, on average, 2.6-3.3% of dose was excreted as 1-OHP in urine and 7.9-10.9% was recovered in bile. Overall, the linear dose-excretion relationship following either exposure routes supports the usefulness of 1-OHP in urine as a bioindicator of polycyclic aromatic hydrocarbon (PAH) exposure. Results further suggest that tissue uptake and distribution of intravenously and orally administered pyrene proceeds similarly. By comparing these data with predicted values from a previously published physiologically based pharmacokinetic model for pyrene in the rat, it also appears that a small fraction of pyrene dose (12%) remains in the body after 24 h and that metabolites other than 1-OHP as measured in the current study are present in significant proportions in urine and feces.

Administration, Oral↗
PubMed1998

Interaction between G-actin and various types of liposomes: A 19F, 31P, and 2H nuclear magnetic resonance study.

We have investigated in the present study the interaction between G-actin and various types of liposomes, zwitterionic, positively charged, and negatively charged. To investigate at the molecular level the conformation of actin in the presence of lipids, we have selectively attached a fluorinated probe, 3-bromo-1,1,1-trifluoropropanone, to the actin cysteine residues 10, 285, and 374 and used high-resolution 19F nuclear magnetic resonance spectroscopy to investigate the probe resonances. The results indicate a change in the mobility of the 19F labels when G-actin is in the presence of positively charged liposomes made of DMPC and stearylamine and in the presence of DMPG, a negatively charged lipid. No conformational change was observed in the actin molecule in the presence of neutral liposomes. Electron micrographs of these systems reveal the formation of paracrystalline arrays of actin filaments at the surface of the positively charged liposomes, while no evidence of actin polymerization or paracrystallization was observed in the presence of DMPG. The interaction between actin and the lipid polar headgroup has also been investigated using solid-state phosphorus and deuterium NMR. The results indicate no evidence of interaction between actin and zwitterionic liposomes but show an interaction between the positively charged liposomes and a negative charge on the actin molecules. Interestingly, the negatively charged liposomes interact with a positive charge, which is most likely associated with the three residues (His-Arg-Lys) preceding the cysteine 374 residue in the protein.

Acetone↗
PubMed1998

Kinetics of tissue distribution and elimination of pyrene and 1-hydroxypyrene following intravenous administration of [14C]pyrene in rats.

The tissue distribution and elimination of pyrene and 1-hydroxypyrene (1-OHP) were evaluated in male Sprague-Dawley rats (210-240 g) following an intravenous injection of 50 micromol/kg of [14C]pyrene. Blood and tissues were removed and urine and feces were collected at 1, 2, 4, 8, 16, and 24 h postdosing. [14C]Pyrene equivalents were measured by liquid scintillation counting, and beta-glucuronidase/arylsulfatase-treated blood, tissues, and excreta were analyzed for pyrene and 1-OHP by HPLC/fluorescence. At 1 h, the largest fraction of the dose was found in adipose tissue, essentially as pyrene, and its elimination followed first-order monophasic kinetics with a half-life (t(1/2)) of 4.9 h. In blood, liver, kidney, lung, muscle, and gastrointestinal (GI) tract, kinetics of [14C]pyrene equivalents were biphasic and average t(1/2) values for the terminal elimination phase (8 to 24 h) ranged between 6.2 and 8.7 h. Elimination of pyrene in blood and these tissues except the GI tract followed first-order biphasic kinetics with average t(1/2) values of the terminal phase ranging between 3.6 and 5.4 h. In the GI tract, a monophasic elimination kinetics of pyrene was observed with mean t(1/2) value of 3.1 h. Kinetics of 1-OHP in blood and liver showed a monophasic elimination with mean t(1/2) values of 6.7 and 6.2 h, respectively. Kinetics of 1-OHP in the other tissues were biphasic with average t(1/2) values of the terminal elimination phase ranging between 5.2 and 6.2 h. At 24 h, on average, 81.7% of the dose was recovered in the urine (57.2%), feces (18.3%), and GI tract (6.2%) as [14C]pyrene equivalents with 2.7 and 1.9% of dose excreted as total 1-OHP in urine and feces, respectively. At all time points, 1-OHP in urine represented a constant fraction of total 14C in urine and feces. These results indicate that (i) [14C]pyrene was rapidly distributed, metabolized, and eliminated from the body, and (ii) although 1-OHP represents a small percentage of total pyrene eliminated from the body, it remains a reliable indicator of systemic exposure to, and overall elimination of the 14C associated with, this polycyclic aromatic hydrocarbon.

Animals↗
PubMed1997

Studies of a second family with the Quebec platelet disorder: evidence that the degradation of the alpha-granule membrane and its soluble contents are not secondary to a defect in targeting proteins to alpha-granules.

We recently described a Quebec family with an autosomal dominant bleeding disorder characterized by mildly reduced-low normal platelet counts, an epinephrine aggregation defect, multimerin deficiency, and proteolytic degradation of several, soluble alpha-granular proteins. Similar clinical features led us to investigate a second family with an unexplained, autosomal dominant bleeding disorder. The affected individuals had reduced to normal platelet counts, absent platelet aggregation with epinephrine, and multimerin deficiency. Their platelet alpha-granular proteins factor V, thrombospondin, von Willebrand factor, fibrinogen, fibronectin, osteonectin, and P-selectin were proteolyzed and comigrated with the degradation products found in patients from the other family. However, their platelet albumin, IgG, external membrane glycoproteins, CD63 (a lysosomal and dense granular protein), calpain, and plasma von Willebrand factor were normal, indicating restriction in the proteins proteolyzed. Electron microscopy studies indicated preserved alpha-granular ultrastructure, despite degradation of soluble and membrane alpha-granular proteins. Immunoelectron microscopy studies of the patients' platelets indicated that fibrinogen, von Willebrand factor, P-selectin, multimerin, and factor V were within alpha-granules, with normal to reduced labeling for these proteins. Pathologic proteolysis of alpha-granular contents, rather than a defect in targeting proteins to alpha-granules, may be the cause of the protein degradation in the Quebec platelet disorder.

Adult↗
PubMed1997

The characterization of novel Pax genes of the sea urchin and Drosophila reveal an ancient evolutionary origin of the Pax2/5/8 subfamily.

The developmental control genes of the Pax family can be grouped into different subclasses according to structure and sequence homology. Here we describe the isolation and characterization of three novel Pax genes of the sea urchin for which no homologues are yet known in other animal phyla. One of these genes, suPaxB, codes for the previously characterized transcription factor TSAP which is involved in the developmental regulation of two pairs of late histone genes. Furthermore, conserved members of the Pax2/5/8 subfamily, which have so far been described only in vertebrates, were isolated not only from the sea urchin, but also from Drosophila and C. elegans. Hence, the Pax2/5/8 transcription factors constitute an ancient subfamily of highly conserved Pax proteins. During Drosophila embryogenesis, the Pax258 gene is shown to be expressed in the precursor cells of the external sensory organs, thus suggesting a role for Pax258 in the early development of the peripheral nervous system of insects.

Amino Acid Sequence↗
PubMed1997

Fibrinogen degradation products in patients with the Quebec platelet disorder.

The Quebec platelet disorder is a serious bleeding disorder associated with proteolysis of alpha-granular proteins, including fibrinogen. We evaluated fibrinogen degradation product (FDP) assays as screening tests for this disorder. Patients with the Quebec platelet disorder (13/13) had elevated serum FDPs (P < 0.01) due to secreted degraded platelet fibrinogen, but normal plasma FDPs and D-dimers. Unrelated controls with bleeding disorders (32/34) had undetectable FDPs, and controls with FDPs due to disseminated intravascular coagulation (DIC) and other illnesses (11/11) had elevated FDPs in all assays (P < 0.01). Immunoblot analyses indicated plasma fibrinogen was normal in the Quebec patients and platelet FDPs were found in their platelet lysates, releasates and serum samples. Their platelet FDPs were not altered by treatment with fibrinolytic inhibitors and were different from the FDPs in DIC and in plasmin-digested fibrinogen. Tests for serum FDPs may provide a simple rapid way to screen for the Quebec platelet disorder.

Antifibrinolytic Agents↗
PubMed1997

Urinary excretion of benzo[a]pyrene metabolites following intravenous, oral, and cutaneous benzo[a]pyrene administration.

The effect of the administration route, dose, and sampling time on the total urinary excretion of four major benzo[a]pyrene (BaP) metabolites, 3-hydroxyBaP (3-OHBaP), 9-hydroxyBaP 9-hydroxyBaP (9-OHBaP), trans-4,5-dihydrodiolBaP (4,5-diolBaP), and trans-9,10-dihydrodiolBaP (9,10-diolBaP), was studied in male Sprague-Dawley rats exposed to a single intravenous, oral, and cutaneous dose of 2, 6, 20, and 60 mumol BaP/kg. Urine samples were collected at 24-h intervals following treatment. Over the 0-72 h period and for a given dose, amounts of BaP metabolites were 3-OHBaP > 4,5-diolBaP > > 9-OHBaP following intravenous and oral dosing, and 3-OHBaP > > 9-OHBaP > or = 4,5-diolBaP after cutaneous treatment. 9,10-diolBaP was barely detected. On the other hand, amounts of 3-OHBaP and 4,5-diolBaP excreted in urine over the 0-72 h period and for a given dose appeared in the following order: intravenous approximately oral > or = cutaneous. Amounts of 9-OHBaP excreted varied as follows: oral > or = cutaneous > intravenous. For all routes of administration, excretion of 4,5-diolBaP was almost complete over the 0-24 h period in contrast with 3-OHBaP and 9-OHBaP. Peak excretion of 3-OHBaP and 9-OHBaP was reached in the 0-24 h period following intravenous and oral treatment and in the 24-48 h period following cutaneous application. Overall, for a given administration route and dose, there were variations in the time profiles between metabolites. In general, there was nonetheless a good correlation between the BaP dose and urinary excretion of 3-OHBaP, 9-OHBaP, and 4,5-diolBaP. Furthermore, total urinary excretion of a specific metabolite, its time profile, and the relative proportion of the metabolites studied depended on the administration route. Data also suggest that a measure of the concentration ratio of the different metabolites could reflect the time and main route of exposure.

Administration, Cutaneous↗
PubMed1996

Membrane fluidity response to odorants as seen by 2H-NMR and infrared spectroscopy.

Fourier transform infrared spectroscopy (FTIR) and deuterium nuclear magnetic resonance spectroscopy (2H-NMR) have been used to study the location of two odorants, beta-ionone and menthone, in a model membrane of dimyristoylphosphatidylcholine, as well as the effect of the odorants on the structure and dynamics of the phospholipids. The interaction has been investigated for two lipid-to-odorant molar ratios, 10:1 and 1:1. The two odorants were found to affect the fluidity of the membrane. More specifically, the 2H-NMR results indicate that at a lipid-to-odorant molar ratio of 10:1, both beta-ionone and menthone increase the order of the deuterons in the interfacial and headgroup regions of the lipid while the incorporation of the odorants at a lipid-to-odorant molar ratio of 1:1 decreases the order of both the lipid headgroup and acyl chains. On the other hand, the infrared results show that the incorporation of beta-ionone and menthone decreases the phase transition temperature and cooperativity of the lipid acyl chains. The results suggest that the site of incorporation of beta-ionone and menthone is very similar in DMPC membranes.

Dimyristoylphosphatidylcholine↗
PubMed1996

Measurement of mouse anti-phospholipid antibodies to solid-phase microspheres by both flow cytofluorometry and Alcian blue-pretreated microtitre plates in an ELISA.

Conventional solid-phase immunoassays measuring interactions between anti-phospholipid antibodies and phospholipids are generally characterized by problems of reproducibility and high levels of non-specific binding. Here we describe two immunoassays based on the use of phospholipids in the form of solid-phase microspheres to measure the presence of anti-phospholipid antibodies in sera. Following the production of antibodies in mice against liposomes containing lipid A, we show that flow cytofluorometric analysis provides a reproducible and sensitive way to detect anti-phospholipid antibodies. We also present a sensitive, rapid and reproducible enzyme-linked immunosorbent assay (ELISA) using Alcian blue pretreated microtitre plates and solid-phase microspheres as coating antigen. This ELISA permitted the detection of antibodies to 1/1000 dilution, while untreated plates gave negative results. Such modified ELISA procedures may be applicable to other types of molecule exhibiting solid-phase binding problems e.g. synthetic peptides (J. Immunol. Methods 175 (1994) 131-135).

Alcian Blue↗
PubMed1996

Urinary excretion kinetics of pyrene and benzo(a)pyrene metabolites following intravenous administration of the parent compounds or the metabolites.

The detailed urinary excretion profiles of 1-hydroxypyrene (1-OHP) and benzo(a)pyrene (BaP) metabolites were studied following acute intravenous administration of pyrene and BaP, respectively, or after injection of the metabolites themselves. Male Sprague-Dawley rats were exposed to 4 mumol 1-OHP/kg or 15 mumol pyrene/kg. Other rats were exposed to 2 mumol/kg of a mixture of four BaP metabolites (3-hydroxyBaP (3-OHBaP), 9-hydroxyBaP (9-OHBaP), trans-4,5-dihydrodiolBaP (4,5-diolBaP), and trans-9,10-dihydrodiol (9,10-diolBaP)) or 40 mumol BaP/kg. Urine samples were collected at frequent intervals over 48 or 96 hr. Injection of both pyrene and 1-OHP produced similar biphasic excretion profiles. An apparent first order half life of 6.9 and 6.6 hr, respectively, could be calculated for the second phase of elimination. Comparable 3-OHBaP excretion profiles were obtained after injection of BaP or a mixture of BaP metabolites. Elimination kinetics showed at least two steps, the second step having a first order apparent half life of 8.1 and 7.6 hr following BaP and BaP metabolites injection, respectively. Time profiles of 4,5-diolBaP excretion following administration of BaP or a mixture of BaP metabolites were almost identical. Elimination was linear and a first order apparent half life of 3.1 and 3.6 hr could be calculated. Elimination of 4,5-diolBaP was much more rapid than that of 3-OHBaP and complete within 24 hr postdosing. Therefore, results suggest that (1) phase I biotransformation is not the rate-limiting step in the excretion of 1-OHP, and 3-OHBaP and 4,5-diolBaP following injection of pyrene and BaP, respectively and (2) similarities in the first order apparent half life of 3-OHBaP and 1-OHP for the late phase of excretion suggest that 1-OHP could be a good surrogate for 3-OHBaP.

Animals↗
PubMed1996

Hemodynamic indices of myocardial dysfunction correlate with dipyridamole thallium-201 SPECT.

UNLABELLED: Important differences in hemodynamics and tracer kinetics occur with dipyridamole compared to exercise scintigraphy. To better understand the clinical significance of dipyridamole SPECT 201Tl scintigraphy, we examined the relationships between scintigraphy and clinical, and angiographic and hemodynamic variables in patients with CAD. METHODS: Forty-nine subjects were divided into three study groups. Patients in Groups A (n = 11) and B (n = 20) had a low (<5%) likelihood of CAD. Group A underwent maximal exercise thallium stress testing. Group B underwent thallium dipyridamole scintigraphy. Group C (n = 18) consisted of patients with coronary artery disease who had dipyridamole thallium scintigraphy and cardiac catheterization within 2 wk. Thallium lung-to-myocardial ratio (L/M), left ventricular dilation and perfusion defect site were compared to hemodynamic, clinical and angiographic variables. RESULTS: The Group A L/M ratio of 0.23 +/- 0.05 (mean +/- 1 s.d.) was significantly lower (p < 0.001) compared to the Group B L/M ratio of 0.31 +/- 0.05. In Group C, the UM ratio showed correlation with indices of left ventricular dysfunction including lower resting ejection fraction (p = 0.02, r = 0.83), higher pulmonary capillary wedge pressure (p = 0.01, r = 0.58) and lower cardiac index (p = 0.03, r = 0.54). Left ventricular dilation was associated with hemodynamic changes of ventricular failure including lower resting ejection fraction (p = 0.008, r = 0.88) and higher pulmonary capillary wedge pressure (p = 0.02, r =0.54). Immediate and delayed perfusion defect size showed good correlation with lower resting left ventricular ejection fraction (p = 0.02, r = 0.83, and p = 0.004, r = 0.91, respectively). CONCLUSION: Lung uptake, left ventricular dilation and perfusion defect size show good correlation to hemodynamic indices of resting left ventricular dysfunction. A combination of these factors may be a better predictor of future cardiac events and prognosis.

Cardiac Catheterization↗
PubMed1995

Benzo(a)pyrenediolepoxide-hemoglobin adducts and 3-hydroxy-benzo(a)pyrene urinary excretion profiles in rats subchronically exposed to benzo(a)pyrene.

The time profiles of benzo(a)pyrenediolepoxide (BaPDE)-hemoglobin (Hb) adduct formation and 3-hydroxybenzo(a)pyrene (3-OHBaP) urinary excretion were studied in male Sprague-Dawley rats exposed to daily benzo(a)pyrene (BaP) intraperitoneal doses of 1.25, 6.25, and 31.25 mumol/kg administered Tuesday to Friday for 4 consecutive weeks. Blood was withdrawn weekly, on Tuesdays, prior to dosing. Twenty-four-hour urine samples were collected on Mondays (following 72 h without treatment) and Thursdays. Analytes were quantified by high performance liquid chromatography (HPLC)/fluorescence. Exposure to BaP resulted in the accumulation of BaPDE-Hb adducts, reaching an average of 1.2 +/- 0.3, 8.3 +/- 1.9, and 38.2 +/- 6.1 pmol/g Hb for the 1.25, 6.25, and 31.25 mumol/kg per day doses after 4 weeks of treatment. The expected saw tooth excretion profile of 3-OHBaP was observed, with peaks on Thursdays and troughs on Mondays, and showed a progressive rise on both Mondays and Thursdays. Increase in Monday values with time suggested a possible increase in BaP body burden during exposure. To verify this aspect further, the urinary excretion kinetic of 3-OHBaP following acute intraperitoneal dosing (31.25 mumol/kg) was determined. Urine samples were collected at frequent timed intervals for up to 164 h post-dosing. Two-step elimination was observed, the second step having a half-life of 25 h, presumably linked to the slow release of BaP accumulated in fatty tissues upon repeated treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1995

High-speed magic angle spinning solid-state 1H nuclear magnetic resonance study of the conformation of gramicidin A in lipid bilayers.

One- and two-dimensional solid-state 1H nuclear magnetic resonance spectra of gramicidin A incorporated in a dimyristoylphosphatidylcholine membrane have been obtained with use of high-speed magic angle spinning. By rotating the sample at 13 kHz, it is possible to observe signals in the 1H spectra between 6.0 and 9.0 ppm attributable to the aromatic protons of the tryptophan residues and the formyl group proton of gramicidin A. Two-dimensional solid-state COSY spectra provided information for the peak assignments. Moreover, changes in the 1H spectra have been observed as a function of the co-solubilization solvent initially used to prepare the samples and therefore as a function of the conformation adopted by gramicidin A. Three organic solvents have been used: trifluoroethanol, a mixture of methanol/chloroform (1:1 v/v), and ethanol. The conformational interconversion of gramicidin A from the double helix conformation to the channel structure for the sample prepared from ethanol was confirmed by following the time evolution of the proton spectra.

Biophysical Phenomena↗
PubMed1994

Improved procedure for the high-performance liquid chromatographic determination of monohydroxylated PAH metabolites in urine.

An improved high-performance liquid chromatographic (HPLC) method for the determination of 3-hydroxybenzo(a)pyrene (3-OHBaP) in urine was developed. The sensitivity and reproducibility of the technique was greatly improved by the addition of 1 mg/L ascorbic acid to the methanol eluent of the HPLC system. This procedure also eliminated the peak splitting and band broadening of the 3-OHBaP peak otherwise observed. Furthermore, it corrected the urine matrix effect on the slope of standard curves. In fact, in the absence of ascorbic acid in the HPLC system, slopes of standard curves were steeper when prepared in a methanolic extract of control rat urine (121 L.nmol-1) than in methanol only (86 L.nmol-1). Both these slopes were smaller than that obtained with the modified mobile phase (244 L.nmol-1). The effect of the latter on the shape and intensity of the 1-hydroxypyrene (1-OHP) chromatographic peak was also investigated. Again, slopes were greater when the standards, prepared in a methanolic extract of urine, were chromatographed with ascorbic acid (380 L.nmol-1) than without (157 L.nmol-1). Therefore, it seems that ascorbic acid, like certain substances in urine, may act by masking specific adsorption sites--probably uncapped silanol residues on the LC 18 column that can retain free 3-OHBaP and 1-OHP metabolites.

Animals↗