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Biomedical subjects

M Porvaznik

Publications and source records attributed to M Porvaznik.

At least 19 recordsLinked to original sources
PubMed1995

Identification of parent benzodiazepines by gas chromotography/mass spectroscopy (GC/MS) from urinary extracts treated with B-glucuronidase.

Urinary glucuronide metabolites of the benzodiazepines were converted back to the parent molecules after treatment with B-glucuronidase. The benzodiazepines were extracted by a one-step liquid/liquid extraction from urine or by a liquid/solid phase extraction. For the limit of detection (LOD), a standard solution of diazepam and oxazepam was serially diluted and analyzed to the point at which a reproducible analytical result was no longer obtained. Using a temperature program and a splitless mode of injection, excellent quantitation was achieved within an 8-min run time. Based upon specimens obtained from patients under a physician's care, we have determined that urinary concentrations of the benzodiazepines > 200 ng/ml are most likely due to abuse rather than to a prescribed ingestion under strict medical surveillance. Therefore, the calibration standard and cutoff concentration for a positive result was set at 200 ng/ml.

Alprazolam↗
PubMed1993

Effect of pre-enlistment testing on the confirmed drug-positive rate for Navy recruits.

In June 1988, the armed forces of the United States began testing prospective candidates for military service for alcohol, marijuana metabolite (THC-COOH), and cocaine metabolite (benzoylecgonine) through the Military Entrance Processing Station (MEPS) program. Comparison of the confirmed positive drug rates for pre-inductees into the Navy during the MEPS program testing period with the confirmed drug-positive rates for 5 years before and 1 year after MEPS testing showed a decrease in the confirmed positive rate for THC-COOH and an apparent initial decrease for cocaine metabolite as a result of MEPS testing. The overall results for cocaine seem to be overshadowed by other demographic factors operating in the population tested.

Adolescent↗
PubMed1992

Creatinine analysis in single collection urine specimens.

Controlled and uncontrolled fluid intake studies were conducted on series of volunteers over the 6 or 12 h of the study periods. Urine specimens were obtained from each subject randomly or at specified times relative to fluid ingestion. Creatinine analysis performed by a modification of the Abbott TDx procedure demonstrates that the values obtained from single collection specimens fall almost in the same range as the values from 24 h pooled collection specimens. The creatinine concentration can be used to indicate possible adulteration of urine specimens by dilution as a means of avoiding detection of use of drugs of abuse. Between 4 and 7 h are required for a decrease in creatinine concentration to about 100 mg/dL from an initial mean of about 170 mg/dL. A minimum of 6 h is needed for any creatinine value to fall to 50 mg/dL or less. Thus, it appears that creatinine output is sensitive to the amount of fluid ingested, but the relationship is neither linear nor immediate. The absence of a significant creatinine concentration in a specimen can be used as an indication of direct or indirect adulteration of the urine specimen by dilution or replacement with water. At NDSL-Great Lakes, a decline of the creatinine concentration to 30 mg/dL is used as a cutoff for differentiating between urine specimens that might have been tampered with to avoid detection of drug use and those specimens that are dilute for other reasons. Values at 10 mg/dL or less are suggestive of replacement by water. The information is provided to local commands for investigation prior to initiation of punitive action by the command.

Creatinine↗
PubMed1992

Factors influencing confirmed drug positives for Navy and Marine Corps recruits.

Confirmed use of marijuana and cocaine in Navy and Marine Corps recruit populations was examined in terms of age, month of enlistment, recruit class size, education level, and Armed Forces Qualifications Test (AFQT) scores. Between 1982 and 1989, confirmed use of the drugs showed a seasonal variation, with the highest levels in the fall and winter. The rate for marijuana and cocaine was inversely related to the size of the recruit class (r = -0.80) and completion of high school (r = -0.82). The recruit class is larger and younger in the summer. AFQT scores were directly related to age. Education level appears to be one major determinant in addressing drug use.

Adolescent↗
PubMed1987

tri-n-Butyltin: a membrane toxicant.

Increased use of the biocidal compound tri-n-butyltin (TBT) in antifouling paints has prompted research aimed at determining the mechanism for TBT toxicity. Past investigations indicate that the primary cellular target for TBT is the cell membrane. Erythrocyte suspensions treated with TBT concentrations 2 greater than or equal to 5 microM undergo hemolysis described by a sigmoidal kinetic pattern. Transformation of cell shape from discocyte to echinocyte occurs at TBT concentrations greater than or equal to 0.1 microM, indicating that the compound enters the outer membrane bilayer. TBT at concentrations greater than or equal to 10 microM forms electron-dense aggregates that are intercalated within plasma membranes as viewed in ultrathin sections by transmission electron microscopy. Qualitative X-ray microanalysis of these aggregates confirms the presence of tin. The size of these structures can be modified by either 10 mM cyanide or 2,3-dimercaptopropanol (British Anti-Lewisite, BAL). Adding 10 mM cyanide to hemolytic TBT concentrations resulted in a synergistic stimulation of hemolysis attributable to high cyanide anion concentrations in or near the cell membrane. The elevated cyanide anion levels are thought to contribute to membrane lysis. The lipophilic dimercapto compounds BAL, dithiothreitol, and 2,3-dimercaptosuccinate are effective inhibitors of TBT-induced lysis. Water-soluble 2,3-dimercapto-1-propane sulfonate, a BAL analog, was largely ineffective as an inhibitor. The detailed molecular mechanism for TBT-induced membrane lysis is not yet clear. Cellular ATP depletion could be induced by TBT as well as by delipidation of anionic phospholipids or even formation of tributylstannylperoxy radicals, resulting in lipid peroxidation.

Chemical Phenomena↗
PubMed1987

Organotin-induced hemolysis, shape transformation and intramembranous aggregates in human erythrocytes.

Organotin compounds examined in this study exhibited a relative order of potency for induction of in vitro hemolysis in human erythrocytes as follows: tri-n-butyltin greater than tri-n-propyltin greater than tetra-n-butyltin greater than triphenyltin chloride greater than tri-n-ethyltin bromide greater than dibutyltin dichloride greater than stannous chloride greater than tri-n-methyltin chloride = butyltin chloride dihydroxide. All of the organotin compounds induced erythrocyte shape transformation from the normal discocyte to an echinocyte and, in addition, triphenyltin chloride, tetra-n-butyltin and tri-n-ethyltin bromide also elicited stomatocyte formation at higher concentrations. Select organotin compounds also formed tin-containing aggregates within the plasma membrane. The relative order of effectiveness for organotin induction of intramembranous aggregates was tri-n-butyltin greater than tri-n-propyltin greater than tetra-n-butyltin greater than tri-n-ethyltin bromide, which was based upon the lowest concentration at which they were observed. These results support the previously suggested theory that organotins are membrane effectors because of their comparatively high hydrophobic, lipid partitioning properties. The relatively lipophilic compound, triphenyltin chloride, appeared to be anomalous because it did not readily promote hemolysis or induce the formation of intramembranous aggregates in human erythrocytes. A log-linear statistical model demonstrated an association of hemolysis with both tri-n-butyltin aggregate formation and shape transformation. Select organotin compounds should be useful probes in membrane studies because of their numerous effects.

Erythrocyte Aggregation↗
PubMed1986

Cyanide stimulation of tri-N-butyltin mediated hemolysis.

The effects of tributyltin and sodium cyanide on hemolysis in human erythrocytes are described. Tributyltin has a sharp cut-off concentration for induction of hemolysis. A 5 microM concentration of tributyltin induces hemolysis and 1 microM or less does not in erythrocyte suspensions with 2.3 X 10(8) cells per ml. The kinetics for tributyltin-induced hemolysis are sigmoidal indicating a complex molecular mechanism leading to lysis. Ten mM sodium cyanide plus 1 microM tributyltin does not stimulate hemolysis rates above levels observed with 10 mM sodium cyanide alone. Five mM sodium cyanide plus hemolytic concentrations of tributyltin stimulates hemolysis rates synergistically compared with either cyanide or tributyltin alone. Ultrastructurally, hemolytic concentrations of tributyltin can be visualized in the electron microscope by osmium staining during fixation as electron-dense spheres penetrating the lipid bilayer of the erythrocyte plasma membrane. Ten mM sodium cyanide plus 25 microM tributyltin increases slightly the size of osmiophilic structures in erythrocyte membranes compared with those spheres seen in cells exposed to 25 microM tributyltin alone. Sodium cyanide is the only compound tested that stimulates tributyltin-induced hemolysis. Sodium thiocyanate, previously shown to be rapidly exchanged across erythrocyte membranes by tributyltin, reduces the rate of hemolysis. It is likely that sodium cyanide stimulates hemolysis in the presence of hemolytic tributyltin concentrations because the multimolecular, membrane-intercalated, tributyltin aggregates are transporting cyanide anion by the electrically silent, anion exchange mechanism demonstrated for other anions. It is suggested that this mechanism delivers cyanide anion to or near critical membrane sites where it is available for enzyme inhibition or cross-linking of protein sulfhydryl groups.

Cyanides↗
PubMed1986

Inhibition of tributyltin mediated hemolysis by mercapto compounds.

Hydrophobic tributyltin (TBT) compounds at concentrations greater than 10 microM caused hemolysis of human erythrocytes and formed structures in plasma membranes. The mercapto compounds, beta-mercaptoethanol (beta MER), 2,3-dimercaptopropanol (BAL), 2,3-dimercapto-1-propane sulfonate (DMPS), DL-dithiothreitol (DTT), and meso-2,3-dimercaptosuccinic acid (DMSA) were examined for their ability to inhibit TBT mediated hemolysis. The relative order of effectiveness for inhibition of TBT mediated hemolysis was BAL greater than DTT greater than DMSA greater than DMPS greater than beta MER. A four-fold excess of BAL over TBT prevented hemolysis for 4 hrs and addition of BAL 0.5 hr after TBT reduced the rate of hemolysis. The number of membrane associated TBT aggregates observed per cell profile decreased as the BAL concentration increased from 0 to 100 microM. However, the mean diameter of TBT aggregates nearly doubled in erythrocyte suspensions at 100 microM BAL. Reactions of dimercapto compounds with lipophilic TBT aggregates may depend on their relative lipid solubilities. Also, conversion of the weak Lewis acid, TBT, from a four to a five or six-coordinate tin adduct by the dimercapto Lewis bases used could also be a factor slowing hemolysis rates.

Erythrocytes↗
PubMed1986

The ultrastructural localization of tri-n-butyltin in human erythrocyte membranes during shape transformation leading to hemolysis.

Scanning electron microscopy, transmission electron microscopy, freeze-fracture, and x-ray energy dispersive spectrometry were used to localize tri-n-butyltin (TBT) in human erythrocytes (RBC's). TBT induced a rapid shape transformation of the RBC discocyte to an echinocyte, which led to hemolysis at concentrations at or above 10 microM TBT. Electron dense spheres or ellipsoids were observed in association with blood cell membranes at or above 10 microM TBT. These structures were visualized initially in thin sections when postfixed with osmium tetroxide. Control cell preparations without TBT did not exhibit these structural densities when fixed with osmium. Freeze-fracture replicas confirmed the presence of TBT aggregates associated with cell membranes as intercalations in the lipid bilayer. In thin sections, these structures measured 71.5 +/- 18.2 nm in diameter. In freeze-fracture replicas of TBT-treated RBC's, particulate structures measuring 60 +/- 18.5 nm in diameter were present on membrane exoplasmic fracture faces and 59.6 +/- 10.8-nm depressions on membrane protoplasmic fracture faces. Qualitative x-ray energy dispersive spectrometry analysis of ultrathin sections of glutaraldehyde-carbohydrazide-embedded samples revealed that the membrane-associated aggregates contained tin. TBT-treated RBC's that were washed with normal saline resulted in a paucity of TBT aggregates associated with the membranes and a reduction in the RBC hemolysis rate. RBC shape transformation occurred at each concentration examined from 0.1 to 100 microM TBT, but was reversible below 1 microM TBT.

Electron Probe Microanalysis↗
PubMed1981

Membrane associations between subsurface cisternae of endoplasmic reticulum and the plasma membrane of rat Sertoli cells.

Close membrane associations between the endoplasmic reticulum and the plasma membrane (ER-PM) occur in specialized regions of the rat Sertoli cell cytoplasm. They are characterized, in freeze fracture replicas, as mesa-like modifications of E membrane fracture faces or as corresponding discoid depressions on P membrane fracture faces. When these structures lie along transitional regions in the membrane fracture plane, they are seen to be complementary, and the space between them to be greatly reduced. These specialized close membrane associations may represent adhesive sites between the endoplasmic reticulum and the plasma membrane. However, their resemblance to vascular endothelial fenestrae which are known to be sites of increased membrane permeability may suggest other functional roles.

Animals↗
PubMed1979

Tight junction development between cultured hepatoma cells: possible stages in assembly and enhancement with dexamethasone.

Freeze-fracture and thin-section methods were used to study tight junction formation between confluent H4-II-E hepatoma cells that were plated in monolayer culture in media with and without dexamethasone, a synthetic glucocorticoid. Three presumptive stages in the genesis of tight junctions were suggested by these studies: 1) "formation zones" (smooth P-fracture face ridges deficient in intramembranous particles), apparently matched across a partially reduced extracellular space, develop between adjacent cells; 2) linear strands and aggregates of 9--11 nm particles collect along the ridges of the formation zones. The extracellular space was always reduced when these structures were found matched with pits in gentle E-face depressions; 3) the linear arrays of particles on the ridges associate within the membranes to form the fibrils characteristic of mature tight junctions. The formation zones resemble tight junctions in terms of size, complexity and the patterns of membrane ridges. Although some of the beaded particle specializations may actually be gap junctions, it is unlikely that all can be interpreted in this way. No other membrane structures were detected that could represent developmental stages of tight junctions. Dexamethasone (at 2 x 10(-6)M) apparently stimulated formation of tight junctions. Treated cultures had a greater number of formation zones and mature tight junctions, although no differences in qualitative features of the junctions were noted.

Animals↗
PubMed1979

Gap junctions between Sertoli and germ cells of rat seminiferous tubules.

Ultrastructural observations of rat seminiferous tubules show clearly the presence of plasma membrane junctions between Sertoli and germ cells in the basal and adluminal compartments. Results obtained from the freeze fracture and thin section techniques were correlated in order to elucidate the nature of these intercellular junctions. We suggest that these intercellular membrane specializations are gap junctions which occur within regions of plasma membrane that also exhibit adherens-like modifications.

Animals↗