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S L Smith

Publications and source records attributed to S L Smith.

At least 181 records · Page 10Linked to original sources
PubMed1989

Covalent interactions of acetaldehyde with the actin/microfilament system.

The covalent binding of [14C]acetaldehyde to purified rabbit skeletal muscle actin was characterized. As we have found for other cytoskeletal proteins, actin formed stable covalent adducts under reductive and non-reductive conditions. Under non-reductive conditions, individual and competition binding studies versus albumin both showed that the G-form of actin is more reactive toward acetaldehyde than the F-form. When proteins were compared on an 'equi-lysine' basis under non-reducing conditions, G-actin was found to preferentially compete with albumin for binding to acetaldehyde. Time-course dialysis studies indicated that acetaldehyde-actin adducts become more stable with prolonged incubation at 37 degrees C. These data raise the possibility that actin could be a preferential target for adduct formation in cellular systems and will serve as the basis for ongoing studies aimed at defining the role of acetaldehyde-protein adducts in ethanol-induced cell injury.

Acetaldehyde↗
PubMed1989

Acetaldehyde substoichiometrically inhibits bovine neurotubulin polymerization.

Acetaldehyde is known to form covalent adducts with tubulin and to inhibit microtubule formation. Available evidence indicates that lysine residues are prominently involved in adduct formation. Previous work has shown that lysines on tubulin can be divided into two general classes based upon their reactivity toward acetaldehyde; those of normal reactivity ("bulk" lysines) and a highly reactive lysine (HRL) located on the alpha-polypeptide subunit. We took advantage of the fact that the HRL is unreactive when tubulin is in the microtubule form to differentiate the effects of bulk from HRL adducts on tubulin polymerization. Under conditions where both bulk lysines and HRL formed adducts, 0.2 mol acetaldehyde/mol tubulin caused complete inhibition of polymerization. When we modified bulk lysines, but not HRL, tubulin polymerized essentially normally. Finally, when we first blocked bulk lysines on microtubules (HRL unreactive) using unlabeled acetaldehyde and then measured the amount of [14C]acetaldehyde adduct formed with tubulin after depolymerization (HRL reactive), 0.08 mol acetaldehyde/mol tubulin resulted in completely impaired polymerization. These data show that microtubule formation is very sensitive to even small mole fractions of acetaldehyde-modified tubulin (especially with HRL) and further suggest that small amounts of acetaldehyde adduct could be damaging to cytoskeleton function in the cell.

Acetaldehyde↗
PubMed1988

Effects of the chitin synthetase inhibitor plumbagin and its 2-demethyl derivative juglone on insect ecdysone 20-monooxygenase activity.

The chitin synthetase inhibitor plumbagin and its 2-demethyl derivative juglone were found to inhibit in a dose-response fashion the cytochrome P-450 dependent ecdysone 20-monooxygenase activity associated with adult female Aedes aegypti, wandering stage larvae of Drosophila melanogaster, and fat body and midgut from last instar larvae of Manduca sexta. The concentration of these naphthoquinones required to elicit a 50% inhibition of the steroid hydroxylase activity in all the insects was approximately 1 x 10(-4) M.

Aedes↗
PubMed1988

Effects of azadirachtin on insect cytochrome P-450 dependent ecdysone 20-monooxygenase activity.

The effects of the insect growth and ecdysis inhibitor azadirachtin on ecdysone 20-monooxygenase activity were examined in three insect species. Homogenates of wandering stage third instar larvae of Drosophila melanogaster, or abdomens from adult female Aedes aegypti, or fat body or midgut from last instar larvae of Manduca sexta were incubated with radiolabelled ecdysone and increasing concentrations of azadirachtin and the ecdysone 20-monoxygenase activity quantified by radioassay. Azadirachtin was found to inhibit in a dose-response fashion the ecdysone 20-monooxygenase activity associated with all the insect preparations. The concentration of azadirachtin required to elicit approximately 50% inhibition of the ecdysone 20-monooxygenase activity ranged from a low of 1 x 10(-4) M for Drosophila to a high of 4 x 10(-4) M for Manduca midgut.

Animals↗
PubMed1988

The effects of acute and repeated administration of T3 to mice on 5-HT1 and 5-HT2 function in the brain and its influence on the actions of repeated electroconvulsive shock.

The effects of the administration of L-triiodothyronine (T3) On the function of 5-HT in the CNS and its influence on the actions of electroconvulsive shock have been examined in mice. A single injection of T3 (100 micrograms/kg) had no effect 24 hr later on either 5-HT1A-mediated hypothermia, induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.5 mg/kg) or the 5-HT1B-mediated locomotor response to 5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl) 1-H-indole (RU 24969; 50 ng i.c.v.). This treatment increased 5-HT2-induced head-twitches, produced by 5-methoxy-N,N'-dimethyltryptamine (5-MeODMT; 2 mg/kg), but did not alter 5-HT2 receptors in the frontal cortex, suggesting that this potentiation was mediated indirectly through a modulatory neurotransmitter. One injection of T3 had no effect on the concentration of 5-HT in the forebrain or mid/hindbrain, but increased 5-HIAA in the latter region. Daily injections of T3 for 10 days attenuated the responses to both 8-OH-DPAT and RU 24969. Furthermore, 5-MeODMT-induced head-twitches returned to control values and this was accompanied by a 10% decrease in 5-HT2 receptors in the cortex. Repeated administration of T3 increased levels of 5-HT in mid/hindbrain and concentrations of 5-HIAA both here and in forebrain. Hence, treatment with T3 attenuated the function of 5-HT1A and 5-HT1B receptors, but increased 5-HT2-mediated responses, although the time-courses for these effects were different. Triiodothyronine also enhanced the synthesis and turnover of 5-HT in the brain of the mouse. Repeated electroconvulsive shock (90 V, 1 sec) decreased the hypothermia induced by 8-OH-DPAT. However, 5-MeODMT-induced head-twitches were enhanced by acute and repeated electroconvulsive shock. Administration of T3 together with electroconvulsive shock did not alter the effects of electroconvulsive shock on 5-HT1A-mediated hypothermia, but markedly potentiated its actions on 5-HT2-mediated responses. These findings provide possible pharmacological evidence for the suggested antidepressant effects of T3 and the potentiation of antidepressant therapy by this thyroid hormone.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1987

Specific reduction of N,N-dimethylnitrosamine mutagenicity in Drosophila melanogaster by dimethyl sulfoxide.

Dimethyl sulfoxide (DMSO) used as a solvent has been observed to complicate mutagenicity screens by interacting with tested chemicals to yield false positives or negatives. We have used DMSO as a solvent in the Drosophila melanogaster recessive sex-linked lethal mutation assay and find that it reduces, but does not abolish, the detectable mutagenicity of N,N-dimethylnitrosamine (DMN). Its use as a solvent with procarbazine, another promutagen, shows no effect on mutagenicity in Drosophila. DMSO does not exhibit a general inhibitory action on microsome activity when ecdysone 20-monooxygenase activity is used as a measure of cytochrome P-450 activity. We were unable to detect the low DMN demethylase activity in the strain used. Hence, the inhibitory effect of DMSO in Drosophila at both the physiological and biological level appears to be limited and not general in action. Because DMN and DMSO are similar in structure, it is possible that DMSO is interacting with a DMN demethylase in Drosophila. This might lead to a reduction in the conversion of DMN to a mutagen. Consequently, from the results of this study and others DMSO should be used cautiously as a solvent in Drosophila mutagen screening.

Animals↗
PubMed1987

Ventricular weights in guinea pigs acclimated to cold plus hypoxia.

Weanling male guinea pigs (Cavia porcellus), 2-3 weeks of age, with initial body weights of 207-271 g were exposed for 2-16 weeks to constant cold (6 degrees C) and hypoxia (PO2 = 85 Torr) equivalent to 4800 m above sea level. Their growth rates and body weights did not differ from those of control animals of the same age maintained under normoxic conditions (22 degrees C, PO2 = 133 Torr). After 2, 3, 4, 6, 10, or 16 weeks exposure the animals were sacrificed, the hearts were removed, the ventricles were separated and weighed, and myoglobin concentrations were determined. Total heart weight as well as both right and left ventricular weights increased linearly with age. By the second week of exposure of the guinea pigs to cold plus hypoxia the total heart and right ventricular weights were 25 and 50% greater than those of the normoxic control animals. Both weights increased at greater rates than those of the controls until Week 6 and then remained at 30 and 80% throughout the 16th week. The weights of the left ventricles in these animals were only slightly greater than those of the controls. In spite of the severe right ventricular hypertrophy these animals showed no clinical signs of right heart failure. Myoglobin concentrations were significantly greater in both ventricles for the cold-plus-hypoxic animals than for the controls.

Acclimatization↗
PubMed1987

Potentiation of atracurium toxicity in isolated rat hepatocytes by inhibition of its hydrolytic degradation pathway.

This study tested the hypothesis that the esters of acrylic acid might be responsible for the previously observed cytotoxic effect of atracurium. Rats were pretreated with triorthotolyl phosphate (TOTP), an inhibitor of the hydrolytic degradation of atracurium. Because hydrolysis of acrylates is also inhibited by TOTP and because the hydrolysis represents a detoxification pathway for these esters, we postulated that the leak of lactic dehydrogenase (LDH) induced by atracurium would be enhanced in hepatocytes harvested from rats pretreated with TOTP. Hepatocytes isolated from rats previously treated with TOTP (25 or 50 mg/kg intraperitoneally, 20 hr before induced death) were incubated for 4 hr in the absence of muscle relaxants or in the presence of either atracurium (0.008-0.8 mM) or metocurine (0.015-0.85 mM). Atracurium produced a concentration-dependent leakage of LDH. The leakage out of cells obtained from TOTP-pretreated rats was greater than was the leakage out of hepatocytes harvested from animals pretreated only with corn oil (a vehicle for TOTP). Metocurine did not produce a leak of LDH. It is concluded that the LDH leakage was produced by ester-type products of atracurium degradation. Acrylates appear to be the toxic agent.

Acrylates↗
PubMed1986

Crystal structure of a novel trimethoprim-resistant dihydrofolate reductase specified in Escherichia coli by R-plasmid R67.

Crystalline R67 dihydrofolate reductase (DHFR) is a dimeric molecule with two identical 78 amino acid subunits, each folded into a beta-barrel conformation. The outer surfaces of the three longest beta strands in each protomer together form a third beta barrel having six strands at the subunit interface. A unique feature of the enzyme structure is that while the intersubunit beta barrel is quite regular over most of its surface, an 8-A "gap" runs the full length of the barrel, disrupting potential hydrogen bonds between beta-strand D in subunit I and the adjacent corresponding strand of subunit II. It is proposed that this deep groove is the NADPH binding site and that the association between protein and cofactor is modulated by hydrogen-bonding interactions along one face of this antiparallel beta-barrel structure. A hypothetical model is proposed for the R67 DHFR-NADPH-folate ternary complex that is consistent with both the known reaction stereoselectivity and the weak binding of 2,4-diamino inhibitors to the plasmid-specified reductase. Geometrical comparison of this model with an experimentally determined structure for chicken DHFR suggests that chromosomal and type II R-plasmid specified enzymes may have independently evolved similar catalytic machinery for substrate reduction.

Drug Resistance, Microbial↗
PubMed1986

Hair loss. Common congenital and acquired causes.

Hair loss is a common problem likely to be encountered by a clinical practitioner. The most frequent causes of hair loss in pediatric patients include tinea capitis, alopecia areata, traction alopecia, and trichotillomania. In the adult population, causes to be considered are alopecia areata and hair loss associated with systemic disease and hormonal influence. The clinician must be able to separate the types and causes of hair loss into those that reflect primary dermatologic conditions and those that represent reaction to systemic disease.

Adolescent↗
PubMed1986

The predictive validity of the functional capacities evaluation.

This study tested the predictive validity of the Functional Capacities Evaluation (FCE), which included the following three components: a Medical History Review, a Client Activity Interview, and the Smith Physical Capacities Evaluation (SMITH-PCE) as the performance component. The FCE is used in conjunction with the Physical Demands and Environmental Conditions specified by the U.S. Department of Labor to predict a subject's ability to return to work. The study used a random sample of 52 subjects. An employment questionnaire served as a criterion measure of predictive validity. The data from the questionnaires were compared with predictions from the evaluations, and a lambdab test was applied to the data. Results suggested that for the sample analyzed, trained registered occupational therapists could use the FCE to predict a client's ability to return to work more accurately. The study was limited in that the sample used was drawn from clients seen in only one private practice and that only 42% of the questionnaires were returned.

Adult↗
PubMed1986

Management of the Zollinger-Ellison syndrome in patients with multiple endocrine neoplasia type I.

Treatment of the Zollinger-Ellison syndrome (ZES) in patients with multiple endocrine neoplasia type I (MEN I) is controversial. Unlike other patients with ZES who have a single tumor and in whom curative surgical resection is possible and desirable, patients with ZES and MEN I tend to have multiple pancreatic islet cell tumors. Therefore the chances for surgical cure are usually different. A retrospective review of 25 patients with ZES as a manifestation of MEN I seen at our institution between 1960 and 1984, an interval during which histamine type 2 (H2) receptor antagonists were introduced, provided an opportunity to study this problem. Follow-up averaged 6 1/2 years. All patients diagnosed before 1979 (14 patients) underwent surgical exploration. Ten patients (71%) had pancreatic procedures (five enucleation, four partial pancreatectomy, and one enucleation of multiple nodules with subsequent total pancreatectomy). None of these procedures was curative, and all patients required further medical and/or surgical therapy for peptic ulceration. Eighteen patients (72%) underwent gastric surgery. Seven patients had subtotal gastrectomy, five of whom required subsequent total gastrectomy. Thirteen patients ultimately had total gastrectomy. There were no immediate postoperative deaths. All patients with diagnoses since 1979 (11 patients) had H2-antagonist therapy as primary treatment. No significant complications were associated with this approach during a mean treatment period of 26 months. Only one of these patients subsequently has required gastric surgery. The proved efficacy of H2 antagonists, coupled with the recognition of the diffuse nature of the pancreatic disease in these patients, has led to a change in the therapeutic approach over the period reviewed. H2-antagonist therapy should be the initial treatment of choice in patients with MEN I who have ZES.

Adult↗
PubMed1986

Evaluation of a stable 5-F prostacyclin analogue as an antithrombotic agent in haemodialysis.

Prostacyclin has been used as a substitute for heparin in renal dialysis because of its potent antiplatelet activity and its short half-life. However, it is difficult to use because of its instability in neutral buffer and its hypotensive activity at antithrombotic doses. SC-39902, a 5-F prostacyclin analogue, has an ED50 of 17.7 micrograms/kg i.v. against ADP-induced thrombocytopenia in rats. The ED25 for hypotensive activity is 7.0 micrograms/kg i.v. The therapeutic index (blood pressure ED25/antiplatelet ED50) of 0.40 is 3.6 times better than that of PGI2 (0.11). SC-39902 supports clot-free dialysis in dogs at 4.0 micrograms/kg/min (ED100 for dialysis) with a 26% change in blood pressure at the 100% effective dose as compared with 0.052 microgram/kg/min required for PGI2 with a 32% change in blood pressure. The authors conclude that SC-39902 will provide the desirable antiplatelet/antithrombotic activities of PGI2 without instability and buffer incompatability problems. However, at the ED100 for dialysis, SC-39902 does have haemodynamic activity and, thus, a therapeutic index which is greater than four times that of PGI2 in rats is required for a PGI2 analogue to have less hypotensive activity during dialysis.

Animals↗
PubMed1986

Comparative toxicity of atracurium and metocurine in isolated rat hepatocytes.

Primary cultures of liver cells isolated from seven rats were used to study the possible toxicity of atracurium and metocurine. The muscle relaxants were separately added to the culture medium and the cells then incubated for 4 hr. The amount of lactic dehydrogenase (LDH) that leaked into the culture medium was determined at the end of incubation. The customary assumption was made that the exudation of LDH reflects the toxic effects of the relaxants. In untreated dishes, approximately 11% of the total intracellular LDH leaked out during the incubation. The net leakage of LDH produced by the relaxants was obtained by subtracting this amount from the LDH activity determined in the media of dishes with the relaxants added. On this basis, metocurine, in concentrations of 12-850 X 10(-6)M, did not cause a net leak of LDH. On the other hand, atracurium, in similar molar concentrations, caused a statistically significant and concentration-dependent leak of LDH that, at its maximum, amounted to more than one half of the intracellular LDH. The results are interpreted in terms of damage to cellular membranes produced by atracurium or its metabolites. Although the exact biochemical process was not identified, we hypothesize that acrylates--produced by Hofmann elimination from atracurium--might be the likely toxic species.

Animals↗