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R D Harbison

Publications and source records attributed to R D Harbison.

At least 55 records · Page 3Linked to original sources
PubMed1984

Evidence for the extreme overestimation of choline acetyltransferase in human sperm, human seminal plasma and rat heart: a case of mistaking carnitine acetyltransferase for choline acetyltransferase.

Detection of choline acetyltransferase (ChAc) in a number of non-neuronal tissues has been extremely overestimated. There are two major types of errors encountered. Type 1 error occurs when endogenous substrates (e.g. L-carnitine) are acetylated by acetyltransferase enzymes (e.g. carnitine acetyltransferase ( CarAc ) ) yielding an acetylated product mistaken for acetylcholine (AcCh). In the past, human sperm and human seminal plasma putative ChAc activity has been extremely overestimated due to Type 1 error. This study demonstrates (1) an endogenous acetyltransferase and substrate activity in human sperm and human seminal plasma forming an acetylated product that is not AcCh but probably acetylcarnitine ( AcCar ); (2) that the addition of 5 mM choline substrate does not significantly increase acetyltransferase activity; (3) that boiled seminal plasma contains an endogenous acetyltransferase substrate which is not choline, but probably L-carnitine. Type 2 error occurs when endogenous carnitine acetyltransferase synthesizes true AcCh, resulting in mistaken evidence for ChAc. This is demonstrated by the fact that the choline substrate Km-value for the neuronal or true ChAc from mouse brain is 0.73 +/- 0.06 mM while the Km-value of choline substrate for purified CarAc from pigeon breast muscle is 108 +/- 4 mM. Type 2 error has occurred for the estimation of putative ChAc in rat heart. The rat heart ChAc was measured in previous studies utilizing a concentration of 30 mM choline substrate. While saturation of neuronal ChAc is observed at 2-5 mM choline, saturation of the rat heart CarAc enzyme is not reached until over 800 mM. Purified CarAc significantly synthesizes AcCh at 30 mM choline. Thus, putative ChAc has been greatly overestimated in the scientific literature for mammalian sperm, human seminal plasma and rat heart.

Acetylation↗
PubMed1984

Paradoxical effects of perturbation of intracellular levels of glutathione on halothane-induced hepatotoxicity in hyperthyroid rats.

Exposure of hyperthyroid rats to halothane results in a centrilobular necrosis of the liver and an 11-fold increase in serum glutamate-pyruvate transaminase (SGPT) levels. These effects are not seen in euthyroid animals. Paradoxically, administration of diethylmaleate to hyperthyroid rats significantly decreased the levels of hepatic glutathione and blocked the halothane-induced hepatic necrosis as well as decreased the elevation of SGPT. In contrast, pretreatment of animals with N-acetylcysteine, an intracellular sulfhydryl repletor , significantly increased the severity of the halothane-induced hepatic necrosis and increased the elevation of SGPT. Similarly, cysteamine, another intracellular sulfhydryl repletor , also exacerbated halothane-induced liver injury. Halothane-induced hepatotoxicity is at least in part apparently regulated by cellular glutathione levels. Paradoxically, glutathione seems to be involved in the bioactivation rather than the detoxification of halothane.

Acetylcysteine↗
PubMed1984

Cocaine-induced hepatotoxicity: lipid peroxidation as a possible mechanism.

In vitro experiments with hepatic washed microsomal preparations showed that malondialdehyde (MDA) formation was increased in a time- and concentration-dependent manner using COC or NC as the substrate. Though 1 mM COC or NC inhibited MDA formation, significant elevations were observed for 100, 10 or 1 microM concentrations. NC at 10 microM after a 30 minute incubation produced a 34% decrease in hepatic microsomal cytochrome P450 whereas 1 mM NC had no such effect. MDA formation in vivo, measured as total absorbance at 535 nm per gram liver, was found to be maximal 4 hours after 40 mg/kg NC ip. Elevations of serum transaminase (SGPT) however were not found until 6 hours after NC. We conclude from these studies that COC and NC induce lipid peroxidation in the liver of PB-pretreated Swiss-origin mice and that peroxidative attack may be a mechanism for hepatotoxicity of these compounds.

Alanine Transaminase↗
PubMed1984

L-alpha-acetylmethadol-induced tissue alterations in mice.

Single oral dosages of the synthetic narcotic analgesic, L-alpha-acetylmethadol (LAAM) increased serum glutamic-pyruvic transaminase (SGPT) levels throughout a two-day observation period and produced a persistent depletion of hepatic and renal glutathione (GSH) levels. These LAAM-induced changes demonstrated dose- and time-dependence within that dosage range producing mortality. Histological evaluation of livers from LAAM-treated mice revealed cytoplasmic and nuclear changes in centrilobular hepatocytes. Interestingly, neither the LAAM-induced histopathological changes nor the depression of hepatic GSH were altered by the induction of hepatic metabolism following pretreatment with either phenobarbital or 3-methylcholanthrene; however, the induction of hepatic drug metabolism did abate the four-day mortality and SGPT elevations.

Alanine Transaminase↗
PubMed1983

Characterization of hyperthyroidism enhancement of halothane-induced hepatotoxicity.

Administration of anesthetic doses of halothane to hyperthyroid male rats results in the development of hepatic necrosis. The severity of the hepatic lesion was dependent on the dose of triiodothyronine (T3) and the length of time it was administered. Pretreatment of rats with iodinated metabolites of thyroxin which do not induce hyperthyroidism did not result in any signs of hepatotoxicity after halothane exposure. The administration of halothane to hyperthyroid female rats or mice of either sex did not result in the development of any overt hepatotoxicity. Likewise, hyperthyroidism did not enhance the hepatotoxicity of another hepatotoxin bromobenzene. The in vitro enzymatic activities associated with cytochrome P-450-dependent metabolism and glutathione S-transferase conjugation activity were markedly altered in hyperthyroid rats. Cytochrome P-450 levels, aminopyrine N-demethylase activity, glutathione levels and glutathione S-transferase activity were all significantly lower in hyperthyroid rats. However, other enzyme activities were stimulated by T3 pretreatment; aniline hydroxylase activity was increased by 45% and cytochrome c reductase activity was increased by 54% in hyperthyroid rats. Glutathione levels were also reduced significantly in hyperthyroid male rats. Maximal changes in both the cytochrome P-450 system and in the glutathione detoxification system were required before halothane demonstrated its hepatotoxic effects. Thus, a new balance between cytochrome P-450-dependent bioactivation and glutathione conjugation of halothane may be necessary for the exaggerated hepatotoxicity of halothane seen in hyperthyroid male rats.

Alanine Transaminase↗
PubMed1983

Perturbation of alpha-aminoisobutyric acid transport in human placental membranes: direct effects by HgCl2, CH3HgCl, and CdCl2.

Mercuric chloride, methylmercuric chloride, and cadmium chloride directly affect the human placental syncytiotrophoblast microvillous membrane. These heavy metals alter the facilitated diffusion of alpha-aminoisobutyric acid (AIB) into vesicles of this membrane in microM concentrations. Mercuric chloride abolishes temporal kinetics of AIB transport, inducing an initial increase in AIB transport (27% at 100 microM) but subsequently lowering equilibrium values when compared to equilibrium time points in control. Methylmercuric chloride and cadmium chloride inhibited the initial rate of AIB transport (40% and 21%, respectively, at 200 microM), but did not affect the equilibrium value of AIB transported when compared to equilibrium levels in control. These effects were concentration dependent. Methylmercuric chloride was more potent in inhibiting AIB transport than cadmium chloride. Methylmercuric chloride and cadmium chloride effects on AIB transport were observed with minimal preincubation with placental vesicles. However, preincubation was necessary for mercuric chloride-induced perturbation of AIB transport. Cysteine protects against mercuric chloride- and methylmercuric chloride-induced effects on AIB transport but did not reverse these perturbations. Mercury- and cadmium-induced placental membrane toxicity result from interactions of these heavy metals with the placental plasma membranes.

Aminoisobutyric Acids↗
PubMed1983

Analysis of maternal alpha-fetoprotein: a comparison of three radioimmunoassays.

Increased levels of alpha-fetoprotein in maternal serum or amniotic fluid may be indicative of a fetal neural tube defect. The present investigation compares, prospectively and retrospectively, the analysis of serum or amniotic fluid alpha-fetoprotein from humans using three radioimmunoassays. A total of 46 sera and 137 prospective and 202 retrospective amniotic fluid samples collected at 12-26 weeks' gestation were assayed using our in-house Farr technique assay, a kit Farr technique assay, and a kit double-antibody assay. Analysis of quality control data in all three assays showed that within- and between-assay variations were less with the double-antibody technique. Additionally, the double-antibody assay offers the advantage of considerably lower nonspecific binding (1.7% vs 16-18% for the Farr technique assays). Of the 375 pregnancies sampled during this study, 340 (91%) resulted in normal singleton births, whereas three (1%) pregnancies were found to have elevated serum or amniotic fluid by all three assay methods and resulted in confirmed neural tube defects. Of the remaining, non-normal outcome without neural tube defect or elevated alpha-fetoprotein was determined in 27 (7%) pregnancies, and false-positive elevated alpha-fetoprotein levels were found for 5 (1%). Analysis of maternal alpha-fetoprotein by radioimmunoassay is a sensitive and accurate adjunct in the prenatal diagnosis of neural tube defects.

Amniotic Fluid↗
PubMed1982

Hepatic glutathione and hepatotoxicity: effects of cytochrome P-450 complexing compounds SKF 525-A, L-alpha acetylmethadol (LAAM), norLAAM, and piperonyl butoxide.

Four compounds forming metabolic intermediate complexes with cytochrome P-450 in vitro were studied for their effects on hepatic glutathione in the mouse. All four compounds depleted glutathione within 1-3 hr after administration. The effect was transient for piperonyl butoxide while lasting at least 24 hr for other compounds. Induction of the mixed-function oxidase system by phenobarbital had no effect on the glutathione-depleting actions of the compounds, but induction with 3-methylcholanthrene abolished the depletion seen with piperonyl butoxide and SKF 525-A. For SKF 525-A, L-alpha-acetylmethadol (LAAM) and norLAAM, the persistent lowering of glutathione was paralleled by elevations in serum glutamic-pyruvic transaminase (SGPT) activity. This depletion of glutathione and subsequent elevations in SGPT were found to be strain and species dependent for SKF 525-A, LAAM and norLAAM. Compounds which complex with cytochrome P-450 in vitro may increase drug toxicities in vivo by mechanisms other than inhibition of oxidative drug metabolism.

Alanine Transaminase↗
PubMed1982

Placental toxicology.

A review is presented of the literature concerning the placenta as a target organ for chemical- and drug-induced injuries that can ultimately lead to teratogenesis or reproductive defects. Such defects can result from the effects of xenobiotics on placental transport, blood flow or pathology, from the metabolism by the placenta of xenobiotics to harmful substances, or from the alteration by xenobiotics of placental endocrine function. Although it is clear that drug- or chemical-induced placental toxicity should be considered as a possible mechanism of teratogenicity, it is an area of research that has been comparatively neglected and is in need of extensive investigation.

Amino Acids↗
PubMed1982

Relation of in vivo drug metabolism to stereoselective fetal hydantoin toxicology in mouse: evaluation of mephenytoin and its metabolite, nirvanol.

Anticonvulsant therapy during pregnancy with the hydantoin phenytoin carries a risk of teratologic sequelae and developmental retardation known as the fetal hydantoin syndrome. The putative teratogen is a highly reactive arene oxide intermediate produced during phenytoin metabolism. By using two structurally similar hydantoins, mephenytoin and its in vivo demethylated metabolite nirvanol, we examined the possibility for a stereoselective dissociation of fetal hydantoin toxicity from maternal anticonvulsant activity. The d-isomers (S-enantiomers) of mephenytoin and nirvanol are p-hydroxylated via an arene oxide and hence were suspect teratogens. The l-isomers (R-enantiomers), being eliminated primarily via alternate pathways, were expected to be less toxic. Equimolar doses of the d- or l-isomers of mephenytoin or nirvanol were administered to pregnant Swiss ICR mice i.p. on gestational day 10. An 8-fold increase in fetal resorptions and a significant 11% decrease in fetal body weight was observed in the group treated with l-nirvanol, whereas no or minimal toxicity was observed in the other treatment groups. The blood clearance for d-nirvanol was double that for l-nirvanol, with correspondingly higher urinary concentrations of arene oxide-mediated metabolites. ANIH shift during metabolism supported the presence of an arene oxide intermediate. Contrary to our expectations, only l-nirvanol, the isomer producing less arene oxide, demonstrated fetal toxicity, thus raising some doubt concerning the arene oxide as the putative hydantoin teratogen. Further animal studies with the d-isomers of mephenytoin and nirvanol may lead to an anticonvulsant of choice during pregnancy.

Animals↗
PubMed1982

Hepatic glutathione and hepatotoxicity: changes induced by selected narcotics.

Propoxyphene and morphine lowered hepatic glutathione and increased serum glutamic-pyruvic transaminase (SGPT) activity when administered to male mice. Maximal changes were seen at 3 to 6 hr after administration, but the effects lasted for as long as 18 hr. Morphine-induced hepatic changes potentiated both acetaminophen and cocaine-induced hepatotoxicity. Naltrexone, a narcotic antagonist, abolished the glutathione depletion produced by both propoxyphene and morphine, but did not alter the propoxyphene-induced elevations of SGPT. Naltrexone also was tested against other narcotic agonists we have previously demonstrated to be hepatotoxic. Naltrexone pretreatment of antagonized L-alpha-acetylmethadol (LAAM)-induced depletion of glutathione and elevations of SGPT. Similarly, naltrexone antagonized norLAAM-induced depletion of glutathione and elevations of SGPT, but only lessened the magnitude of the changes induced by SKF525-A. The narcotic agonists morphine, LAAM, norLAAM and propoxyphene lower hepatic glutathione and induce hepatocellular damage, but these two effects appear to be unrelated.

Acetaminophen↗
PubMed1981

Syncytiotrophoblast membrane vesicles: a model for examining the human placental cholinergic system.

A membrane vesicle preparation was used to examine characteristics of the human placental cholinergic system. Plasma membrane vesicles were prepared from the microvillous surface of the human placental syncytiotrophoblast. Membranes were purified 18 -to 20-fold as indicated by 5'-nucleotidase activity. Vesicle cholinesterase activity was enriched and had a substrate preference consistent with that of acetylcholinesterase (acetylcholine greater than acetyl-beta-methylcholine greater than butyryl-choline). Choline acetyltransferase specific activity was reduced 80%. The synthetic muscarinic ligand, [3H]-quinuclidinyl benzilate (QNB), was used to identify two classes of muscarinic cholinergic binding sites. The dissociation constant of QNB binding was 80 pM and 30 nM for the two sites. The sites were saturable and bound 9 fmoles and 910 fmoles per mg protein for the high and low affinity sites, respectively. Specific binding was inhibited by scopolamine, atropine, carbamylcholine (CCH), and diphenhydramine, but not by non-muscarinic ligands-i.e. GABA, glycine, d-amphetamine, kappa-bungarotoxin and nicotine. The cholinergic agonist CCh had no effect on active AIB transport, although pharmacologic doses (lmM) of atropine, scopolamine and lidocaine reduced Na-gradient active transport of kappa-aminoisobutyric acid (AIB). No effect on Na-independent AIB transport was observed. Thus, these drugs apparently reduced AIB uptake through their shared local anesthetic activity and not through a central cholinergic mechanism. In contrast, CCh was able to stimulate Ca2+ uptake by the vesicles in a dose-dependent manner paralleling its ability to inhibit QNB binding. The CCh-stimulated Ca2+ uptake was inhibited by scopolamine, implying its mediation via cholinergic-type binding sites. The membrane vesicle preparation therefore provides a useful model for examination of the role of the human placental cholinergic system.

Acetylcholine↗