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D W Hoffman

Publications and source records attributed to D W Hoffman.

At least 55 records · Page 3Linked to original sources
PubMed1988

Electrochemical detection for high-performance liquid chromatography of ketoconazole in plasma and saliva.

Ketoconazole, cis-1-acetyl-4-[4[[2-(2,4-dichlorophenyl)-2-(1H-imidazol- 1-ylmethyl)-1,3-dioxolan-4-yl]methoxy]phenyl]piperazine, a clinically used antifungal agent, is also an inhibitor of steroid hormone biosynthesis. A high-performance liquid chromatographic method is described which resolves ketoconazole with selectivity and high sensitivity provided by the use of electrochemical detection. Ketoconazole can be detected in high-performance liquid chromatography by electrochemical oxidation at a glassy carbon electrode at a potential of +1.0 V. Electrochemical detection offers improved sensitivity and selectivity over ultraviolet absorbance or fluorescence detection after derivatization. The method utilizes a volatile buffer system compatible with postcolumn analyses and an internal standard which is electrochemically active. This technique provides a simple method to assay ketoconazole. Ketoconazole can be detected in human plasma and saliva after a single oral therapeutic dose.

Chromatography, High Pressure Liquid↗
PubMed1988

Human metabolism of phenothiazines to sulfoxides determined by a new high performance liquid chromatography--electrochemical detection method.

The metabolism of phenothiazine drugs may contribute to both their therapeutic and toxic actions by production of active metabolites in vivo. Idiosyncratic reactions or treatment failure may be a consequence of differing patterns of metabolism in different patients. In this report, a modification of our method for the detection of metabolites of phenothiazines is described, which also permits the simultaneous determination of sulfoxide metabolites in human plasma. Application of this method to human plasma identifies marked individual differences in patterns of phenothiazine metabolism.

Chromatography, High Pressure Liquid↗
PubMed1988

Lateral olivocochlear neurons contain both enkephalin and dynorphin immunoreactivities: immunocytochemical co-localization studies.

Antibodies to methionine enkephalin and to dynorphin B were used in an immunocytochemical study examining co-containment of enkephalins and dynorphins in olivocochlear neurons in the guinea pig lateral superior olive. Two methods of sequential co-localization were employed: one using primary antibodies from different species, the second using elution of antibodies. Co-localization of enkephalin-like and dynorphin-like immunoreactivities was found in lateral olivocochlear neurons, suggesting co-containment of enkephalins and dynorphins in this projection pathway from the lateral superior olive to the organ of Corti.

Animals↗
PubMed1987

Nutritional status, glutathione levels, and ototoxicity of loop diuretics and aminoglycoside antibiotics.

Chinchillas deprived of food for 48 h prior to the administration of a combined dose of ethacrynic acid (10 mg/kg) and kanamycin (100 mg/kg) suffered a profound hearing loss. Fed animals did not demonstrate any hearing loss at the same dose levels. Drug metabolism may be the common pathway by which ototoxic agents interact, by a mechanism which is common to both the cochlea and the kidney. Glutathione (GSH) is a tripeptide which is involved in several pathways in the detoxification of active oxygen and reactive species formed during xenobiotic metabolism. The enhanced auditory dysfunction was paralleled by one-third decline in hepatic glutathione levels in the food-deprived animals. Manipulation of endogenous GSH levels may mitigate the toxicities of many of these drugs, which otherwise limit their clinical usefulness. These results also indicate that nutritional status may have important clinical implications during drug therapy.

Animals↗
PubMed1987

The rates of fast reactions of carbon dioxide and bicarbonate in human erythrocytes measured by carbon-13 NMR.

The application of carbon-13 nuclear magnetic resonance spectroscopy to the study of the kinetics of millisecond timescale reactions of CO2 in human erythrocyte suspensions is described. The rates of intracellular enzyme catalyzed CO2 hydration and HCO3- dehydration were quantitatively determined, as well as the rates of CO2 diffusion into and out of the erythrocytes. The method also provides an accurate measure of the intracellular pH in the range of pH 6.0 to pH 7.0. A temperature dependence study was used to determine the thermodynamic functions for the intracellular hydration-dehydration reaction.

Bicarbonates↗
PubMed1985

Localization and quantitation of proenkephalin-derived neuropeptides in the rat hippocampus.

We have measured the content of met- and leu-enkephalin and dynorphin B in the rat hippocampus, and localized these opioid peptides within the intrinsic hippocampal neuronal circuitry with specific lesions. Several enkephalins, two of which were shown to be met- and leu-enkephalin, were identified in rat hippocampus. The levels of the enkephalin-related peptides were unaffected by intrahippocampal injections of colchicine, which destroyed the great majority of the hippocampal granule cells, while the level of dynorphin B, which serves as a marker for the proenkephalin B-derived peptides, was markedly depleted. Entorhinal cortical lesions ablating the perforant pathway input to the hippocampus did not significantly alter dynorphin B nor enkephalin levels in the hippocampus. Unilateral fimbrial transection caused a small but significant increase in dynorphin B on the side of the lesion relative to the non-lesioned side, although neither side was significantly different from control, while at the same time causing a significant bilateral increase in both met- and leu-enkephalin levels. This may result from loss of a direct or indirect stimulatory input to peptide-containing neurons within the hippocampus. The enkephalins appear to be located in neuronal cell bodies intrinsic to the body of the hippocampus, while the dynorphins are likely to be intrinsic only to the granule cell-mossy fiber system originating in the dentate gyrus.

Animals↗
PubMed1985

Localization of dynorphin B-like and alpha-neoendorphin-like immunoreactivities in the guinea pig organ of Corti.

Antiserum to dynorphin B and antiserum to alpha-neoendorphin were used in an immunocytochemical examination of the guinea pig organ of Corti. Immunoreactive staining for these two proenkephalin B (prodynorphin)-derived peptides was seen in the lateral system of olivocochlear efferents in the organ of Corti: the inner spiral bundle, the tunnel spiral bundle and by the bases of inner hair cells. Immunoreactive staining with both antisera was also seen in efferent terminals on outer hair cells at or above the level of the nucleus, which may represent terminals of either the lateral or the medial system. No immunoreactive staining was seen in tunnel crossing fibers and at bases of outer hair cells corresponding to the medial system of efferents. The staining seen with antiserum to dynorphin B and to alpha-neoendorphin has similar distribution to that seen with antisera to methionine enkephalin; there may be co-localization of these neuropeptides in the lateral system of efferents. Choline acetyltransferase-like immunoreactivity (co-localized with enkephalin-like immunoreactivity in the lateral system in the brainstem) and glutamic acid decarboxylase (GAD)-like immunoreactivity have also been found in olivocochlear efferents. Further studies will be necessary to determine if the dynorphins are co-localized with other neurotransmitter candidates and what their interactions may be.

Animals↗
PubMed1985

Proenkephalin and prodynorphin related neuropeptides in the cochlea.

Dynorphin B (rimorphin), a proenkephalin B (prodynorphin)-derived peptide, and met-enkephalin-Arg6, Gly7, Leu8 (met-enkephalin octapeptide), a proenkephalin A-derived peptide, were identified in the mammalian cochlea by specific radioimmunoassays. The antisera are directed against unique sequences in the peptides, and this immunoreactivity cannot be ascribed to cross-reaction with any other known opioid peptides. Met-enkephalin octapeptide and dynorphin B can for this reason serve as reliable markers for the proenkephalin A- and proenkephalin B-derived peptides, respectively. Lesion studies in the cochlea indicate that dynorphin B is confined to olivocochlear efferents. It has not been determined if the dynorphin-containing neurons are the same as those known to contain enkephalin-related peptides, or if they may be cholinergic. Different, presumably inhibitory, neurotransmitters or modulators in the olivocochlear fibers create the possibility of separately modulating the effects of inner or outer hair cells on auditory nerve activity, and so becoming able to study their individual actions in audition. The olivocochlear fiber-hair cell-eighth nerve interaction may provide a valuable model for a complex multi-transmitter synaptic junction.

Animals↗
PubMed1984

Localization and quantitation of dynorphin B in the rat hippocampus.

The present study measures the content of dynorphin B in the rat hippocampus, and localizes the dynorphins within the intrinsic hippocampal neuronal circuitry. The level of dynorphin B, which is representative of the prodynorphin-derived peptides, was markedly depleted by intrahippocampal injection of colchicine, which destroyed the great majority of the hippocampal granule cells and the associated mossy fiber pathway. The hippocampus contralateral to the injection demonstrated a slight, non-significant rise in dynorphin B levels after colchicine. Entorhinal cortical lesions ablating the perforant pathway input to the hippocampus did not significantly alter dynorphin B levels in the hippocampus. Unilateral fimbrial transection caused a small but significant increase in dynorphin B on the side of the lesion relative to the unlesioned side, but neither side was significantly different from control.

Animals↗
PubMed1984

Several distinct receptor binding enkephalins in olivocochlear fibers and terminals in the organ of Corti.

Biochemical studies centering on the use of reverse-phase high-performance liquid chromatography (HPLC) and radioimmunoassays (RIA) demonstrate the presence in the guinea pig organ of Corti of at least 3 enkephalin-related peptides, two of which are identified as Met- and Leu-enkephalin, respectively. Enkephalins were identified and quantitated by HPLC-RIA in the isolated second turn of the organ of Corti, but were not found in stria vascularis or auditory nerve dissected from the cochlea. Three enkephalin-immunoreactive HPLC fractions inhibited the binding of labeled naloxone to rat brain membranes. All enkephalins identified by the combined HPLC-RIA procedure had an apparent molecular weight similar to that of Met- and leu-enkephalin peptide standards. Immunocytochemistry, performed with the best-characterized Met-enkephalin antiserum used in the RIAs, localized the enkephalin-like immunoreactivity to lateral efferent fibers and terminals under inner hair cells of the organ of Corti. Other antisera raised against Met-enkephalin, not used for RIA, visualized enkephalin-like immunoreactivity in medial efferent fibers under outer hair cells as well. This enkephalin-like immunoreactivity may reflect the presence in the medial efferent system of other structurally similar peptides in addition to those detected biochemically. Efferent fiber lesion, by evulsion of the vestibular nerve close to the vestibulocochlear anastomosis in which the olivocochlear fibers run, eliminated enkephalin-like immunoreactivity and the enkephalin-related peptides identified by HPLC-RIA.

Animals↗
PubMed1984

Effects of chemical and surgical lesions on levels of chromatographically identified enkephalin-like peptides in rat hippocampus.

The present study quantitates the content of Met- and Leu-enkephalin in the rat hippocampus, and provides information on the localization of the enkephalins within the hippocampal neuronal circuitry. Several enkephalins were identified in rat hippocampus, two of which are shown to be Met- and Leu-enkephalin. The levels of these enkephalins, and of other unidentified enkephalin-related peptides, were not depleted by intrahippocampal colchicine, which destroyed the great majority of the hippocampal granule cells and the associated mossy fiber pathway. Entorhinal cortical lesions ablating the perforant pathway input to the hippocampus also did not significantly lower enkephalin levels in the hippocampus. Unilateral fimbrial transection caused a significant bilateral increase in both Met- and Leu-enkephalin levels. This may result from loss of a stimulatory input to putative enkephalin containing interneurons within the hippocampus. The extents of all lesions were verified histologically in hippocampi used for biochemical analysis. No evidence was seen for the presence of enkephalins in the perforant pathway, nor in nerve fibers in the fimbria/fornix, which provide the other main source of hippocampal efferents. The enkephalins are likely to be intrinsic to the hippocampus, in which neuronal cell bodies containing enkephalin-like immunoreactivity have been extensively reported.

Animals↗
PubMed1984

Enkephalin-like immunoreactivity in the guinea pig organ of Corti: ultrastructural and lesion studies.

Enkephalin-like immunoreactivity (ELI) was examined in a light and electron microscopic study of the normal guinea pig cochlea and of cochlea de-efferented through evulsion of the vestibular nerve. Antiserum to methionine enkephalin, 164, which gives immunoreactive labeling of only the lateral system of efferents, and antiserum 163, which gives immunoreactive labeling of lateral and medial efferents, were used. In de-efferented cochleae no immunoreactive labeling was seen with either antiserum, confirming that in the organ of Corti ELI is confined to efferents. At the ultrastructural level antiserum 163 but not 164 showed ELI in efferent terminals at the base of outer hair cells. ELI with 164 was seen in efferents ending on outer hair cells at the level of the nucleus. Medially, ELI was seen with both antisera in the inner and tunnel spiral bundles. Efferent terminals containing ELI were seen apposing afferent dendrites, other efferents and the inner hair cell. However, only rarely could synaptic contacts be unambiguously identified and then only with afferent dendrites.

Acetylcholinesterase↗
PubMed1983

Chromatographic identification of enkephalins in the guinea pig retina.

Immunocytochemical localization of enkephalin-like peptides and binding of several opiate ligands have been reported previously in the mammalian retina. High-performance liquid chromatography was used to separate and identify the enkephalin-related peptides in the guinea pig retina. Enkephalin-immunoreactivity in the retina was separated into three distinct fractions, as determined by radioimmunoassay. Two of these fractions were identified as Met- and Leu-enkephalin, respectively. The immunoreactive fractions were also active in inhibiting the binding of [3H]enkephalin to rat brain membranes. All immunoreactive peptides had molecular weights similar to those of the enkephalins, as determined by gel chromatography. These techniques allow us to directly assay and identify enkephalin-related peptides in retinal tissues.

Animals↗
PubMed1983

High-performance liquid chromatographic identification of enkephalin-like peptides in the cochlea.

Met-enkephalin was identified in cochleae from guinea pigs by a combined reversed-phase high-performance liquid chromatographic separation and subsequent radioimmunoassay of the chromatographic fractions. A second Met-enkephalin-immunoreactive fraction was found in the cochlea, with a retention time shorter than that of Met-enkephalin. These findings confirm and extend earlier cytochemical observations, and suggest the differential immunocytochemical staining seen under inner and outer hair cells in the cochlea may be related to different peptides in the two efferent systems innervating the cochlea. Different molecular forms of enkephalin-related peptides may serve different functional or metabolic roles in complex efferent or local regulation of peripheral sensory processing.

Animals↗
PubMed1983

Multiple molecular forms of enkephalins in the guinea pig hippocampus.

The combined techniques of HPLC and radioimmunoassay were used to identify and quantitate enkephalin-related peptides in the guinea pig hippocampus. Both met- and leu-enkephalin were identified, in approximately a 2:1 ratio, as well as a third enkephalin-like molecule that is neither met- nor leu-enkephalin. The third enkephalin elutes earlier than met- or leu-enkephalin from a reversed-phase column, has a molecular weight similar to the other enkephalins, and is as active as these enkephalins are in inhibiting binding of labeled opiates to rat brain membranes. All regions of the hippocampus (dentate gyrus, CA1-2, CA3-4, and subiculum) contain all three immunoreactive peptides. Immunocytochemical techniques, using antisera raised against met-enkephalin, show with one antiserum immunoreactivity in the granule cell-mossy fiber system, and with the other scattered immunoreactive cells mostly in the CA2 region. Enkephalins are not confined to the mossy fiber system, as previously suggested, but may be a component of another hippocampal innervation.

Animals↗
PubMed1982

Immunocytochemical localization of enkephalin-like immunoreactivity in the retina of the guinea pig.

The distribution of enkephalin-like immunoreactivity in the retina of the guinea pig was studied. Indirect immunofluorescence techniques were used on retinae with and without colchicine pretreatment. In retinae not receiving colchicine pretreatment, enkephalin-like immunoreactivity was seen in fibers in the inner plexiform layer, predominantly in laminae 1, 3, and 5. In colchicine-pretreated retinae, enkephalin immunofluorescent cell bodies were seen in the inner margin of the inner nuclear layer in addition to the immunoreactive fibers. These cells showed morphological characteristics of amacrine cells. No enkephalin-like immunofluorescence was seen in the optic nerve, ganglion cell layer, or outer nuclear or plexiform layers. These findings of enkephalin-like immunoreactive cells and fibers in a mammalian retina add to the findings in nonmammalian retinae and suggest that the enkephalins play a role in primary sensory systems of mammalian and nonmammalian species.

Animals↗