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Biomedical subjects

G Levy

Publications and source records attributed to G Levy.

At least 199 records · Page 11Linked to original sources
PubMed1990

Endodontic file design and dynamics in automated root canal preparation. Concepts, materials and methods.

Many treatment failures in endodontics are caused by problems that occurred during canal preparation. This article reviews principles of endodontic instrument design and analyzes the design as it relates to an automated handpiece. After a review of the problems of automation, there will be an introduction of a new automated handpiece and a new modified file known as the Anticurvature File.

Equipment Design↗
PubMed1990

[Myocardial infarction and anti-ethinylestradiol antibody. Apropos of a case in an 18-year-old woman].

An 18-year-old woman presented with a large anterior myocardial infarction. Her cardiovascular risk factors were cigarette smoking in moderation and oral contraception with a synthetic oestroprogestative pill prescribed a few months previously. Coronary angiography showed occlusion of the left anterior descending artery but no other lesions. Biological investigations excluded an abnormality of coagulation. Antibodies to synthetic steroids (ethinylestradiol and progesterone) and circulating immune complexes were found in the serum. The role of antiethinylestradiol antibodies in the mechanism of myocardial infarction is discussed. These antibodies are present in 30 per cent of women taking oral contraceptives and their titres are significantly higher in 90 per cent of women who develop vascular thrombosis unrelated to atherosclerosis. The mechanism of the thrombogenic action of the antibodies and circulating immune complexes is also considered.

Adolescent↗
PubMed1990

Eicosanoids and the liver.

Prostaglandins and leukotrienes are ubiquitous mediators of a wide variety of physiologic and immunologic effects in liver function and disease. Although the biochemical, synthetic and catabolic pathways of these compounds from arachidonic acid are well known, their cellular mechanisms of action are less well understood. Numerous studies have demonstrated the role for leukotrienes in the pathogenesis and the protective action of PG in experimental animal models of liver injury. These have included models of liver cell damage due to ischemia, galactosamine, carbon tetrachloride, and lipopolysaccharide. More importantly, the results of these studies have led to the demonstration of protective properties of 16, 16 dimethyl PGE2 (dm PGE2) in a mouse model of viral hepatitis. These results have led to the use of IV PGE1 in the treatment of patients with fulminant viral hepatitis, where 71% overall survival was observed as well as in the setting of primary non function and recurrent hepatitis B following liver transplantation. While the mechanisms of prostaglandin hepatic protection are not well understood, it has been demonstrated that dm PGE2 abrogates the induction of tumour necrosis factor, leukotriene B4 (LTB4) and procoagulant activity by macrophages as well as attenuating the expression of major histocompatibility class antigens on the surface of hepatocytes, and may inhibit viral replication. Finally, prostaglandins are known to play a role in the renal dysfunction associated with cirrhosis and fulminant hepatic failure, and therefore further studies of these agents in the pathophysiology and treatment of liver diseases and their complications are warranted.

Animals↗
PubMed1990

[Prognosis of canal treatment. Success and failure].

This clinical review confirms the very positive prognosis for endodontic therapy, conditional to strict compliance with imperatives. Endodontics failures are transient and can be remedied. The authors define the attitude to be adopted and the measures to be taken in accordance with the type of difficulty encountered.

Humans↗
PubMed1990

[The radicular post. Specifications].

The radicular pivot, the key component in Richmond and Davis crowns, was initially devised to maintain a permanent link between an artificial crown and the residual root of a monoradicular tooth. The success of such structures depends on three parameters: pivot rigidity (to prevent its fracture or deformation), rigidity of the link of between pivot and artificial crown, permanence of the cemented junction between pivot and root (pivot retentivity).

Crowns↗
PubMed1990

[Preparations for anterior composites].

This paper sets forth and discusses the various preparations used in aesthetic restoration of anterior teeth with composite resins. The clinical description of contours involves treatment of class III and IV carious lesions and correction of aesthetic imperfections which justify resorting to direct techniques of cosmetic dentistry.

Composite Resins↗
PubMed1989

[Healthy carriers].

The vaginal cavity is normally colonized by numerous strains, all "opportunist". Bacteriological tests are therefore unnecessary in most cases and they could not be negative. If it is good to know which conditions keep vaginal germs in a quiescent state, it is especially important not to mistake a normal colonization for a vaginitis and run the risk of disturbing the ecological balance with an unnecessary and dangerous treatment.

Carrier State↗
PubMed1989

Kinetics of drug action in disease states. XXXIII: Disparate effects of pentylenetetrazol in rats as a function of renal disease model and pharmacologic endpoint.

The purpose of this investigation was to determine if the pharmacodynamics of the central nervous system stimulant pentylenetetrazol (PTZ) are altered in renal dysfunction. Female rats subjected to bilateral ureteral ligation (with sham-operated controls) or injected with uranyl nitrate (with saline injected controls) were infused intravenously with PTZ until the onset of either a minimal (myoclonic jerk) or maximal (tonic hindlimb extension) seizure. Neither chemically nor surgically induced renal dysfunction caused a change in the concentrations of PTZ in CSF, serum, or brain at onset of minimal seizures. When PTZ was infused to onset of maximal seizures, the rats with chemically induced renal dysfunction required higher concentrations, whereas the ureter-ligated rats convulsed at lower concentrations of PTZ than did the corresponding control animals. Thus, the effects of experimental renal dysfunction on the convulsant action of PTZ are dependent on both the disease model and the endpoint used for the pharmacodynamic measurement. Apparently, renal dysfunction did not affect the PTZ-induced seizure threshold, but inhibited the spread of seizures. The increased sensitivity of ureter-ligated rats may be due to their pronounced retention of water, since water loading is known to increase seizure susceptibility.

Animals↗
PubMed1989

Relationship between concentration and anticonvulsant effect of phenytoin against electroshock-induced seizures in rats: comparison of sampling sites for concentration determinations.

The purpose of this investigation was to determine the optimum sampling site for phenytoin concentration measurements in the context of pharmacodynamic studies of the anticonvulsant effect of phenytoin. Determination of drug concentrations in the serum, serum water, brain, and cerebrospinal fluid (CSF) of rats as a function of time after iv injection of a 6-mg/kg dose revealed a significant disequilibrium between brain and serum water for 15 min and between CSF and serum water for 5 min after injection. The concentrations of phenytoin in serum water 1 min after injection of 3 mg/kg (0.371 +/- 0.054 microgram/mL) and 45 min after injection of 8 mg/kg (0.399 +/- 0.049 microgram/mL) were not significantly different, but drug concentrations in the CSF and brain were appreciably higher after the latter dose. There was no protection against electroshock-induced seizures 1 min after the 3-mg/kg dose, but there was complete protection 45 min after the 8-mg/kg dose. At 15 min after drug injection, phenytoin concentrations in CSF and serum water were essentially identical over a wide concentration range. Fifty female Lewis rats weighing approximately 225 g, that consistently exhibited maximal electroshock-induced seizures in three preliminary trials on separate days, received 1, 2, 4, 6, or 8 mg/kg of phenytoin by iv injection. Electroshock was applied 15 min later, the percentage of animals protected from seizure by each dose was determined, and drug concentrations in serum, serum water, brain, and CSF were measured by gas chromatography. The relationship between anticonvulsant activity and drug concentration could be described by a Hill-type equation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Comparative pharmacokinetics of coumarin anticoagulants. XLIX: Nonlinear tissue distribution of S-warfarin in rats.

The serum protein binding of the oral anticoagulant drug warfarin varies widely among rats and largely accounts for corresponding variations in the total serum clearance of the drug. The hepatic uptake of warfarin is concentration dependent despite the concentration independence of the free fraction of warfarin in serum over a wide concentration range. This investigation was designed to determine the distribution of the S enantiomer of warfarin in rats as a function of warfarin concentration, free fraction in serum, dose, and time. Two groups of rats, one with relatively low (0.0043) and the other with relatively high (0.0105) average serum free fraction values, were selected from a large number of adult male Sprague-Dawley rats. All animals received an iv injection of S-warfarin, either 0.25 or 1.0 mg/kg, and were sacrificed at intervals over a period of 10 d. Concentrations of S-warfarin in serum, liver, kidneys, muscle, and fat were determined by HPLC. The tissue:serum concentration ratio (T:S) of the drug was highly concentration dependent, but was independent of dose, time, and (except for fat) free fraction in serum. The T:S for fat was higher in animals with the larger serum free fraction values. The T:S of S-warfarin for the liver was greater than 10 at low concentrations and reached a limiting value of 0.25 at relatively high concentrations of the drug. In general, the T:S versus concentration profiles of S-warfarin are consistent with the presence of two classes of binding sites in the tissues, one with very high affinity and low capacity, the other with lower affinity and apparently unlimited capacity under the experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1989

Kinetics of drug action in disease states. XXXII: Effect of experimental hypertension on the pharmacodynamics of phenobarbital in rats.

The purpose of this investigation was to determine the effect of experimental hypertension on the concentrations of phenobarbital required to produce a defined hypnotic effect (loss of righting reflex) in adult, female Lewis rats. Hypertension was induced with deoxycorticosterone acetate (DOCA), administered by im injection (first experiment) or by pellet implant (second experiment), and 1% NaCl in the drinking water. There were two control groups: one that received im injections of water or a drug-free pellet implant plus 1% NaCl in the drinking water, the other that received water injections or drug-free pellet implants and no NaCl in the drinking water. These treatments were carried out for 3 months and resulted in appreciable elevation of blood pressure and increased heart weight in the DOCA + NaCl-treated (but not in the NaCl alone) rats. All animals then received an infusion of phenobarbital until onset of loss of righting reflex. The concentrations of phenobarbital in the serum, serum water, brain, and CSF of the hypertensive rats at the pharmacologic endpoint did not differ significantly from corresponding concentrations in the control groups (except for a marginal difference of the drug concentration in serum water between the DOCA pellet group and the drug-free pellet control group). It is concluded that DOCA-induced hypertension has no apparent effect on the sensitivity of the central nervous system to the hypnotic action of a barbiturate in female rats.

Animals↗
PubMed1989

Effect of enoxacin on theophylline neurotoxicity.

Concomitant use of the bronchodilator theophylline and the antibacterial agent enoxacin has been associated with significant neurologic and other adverse effects. Enoxacin and certain other quinolones are known to inhibit the biotransformation of theophylline, thereby increasing the plasma concentrations of the bronchodilator. It was considered possible that this may not be the only interaction because theophylline as well as enoxacin are known to have neurotoxic potential. To explore the possibility of a pharmacodynamic interaction, rats pretreated orally with enoxacin or water (controls) were slowly infused i.v. with theophylline until the onset of a maximal seizure. Neither 100 nor 400 mg/kg enoxacin 1 hour before the infusion had any significant effect on the infused dose or on the concentrations of theophylline in serum, brain and cerebrospinal fluid at onset of seizures. On the other hand, 400 mg/kg enoxacin reduced the total serum clearance of a 12 mg/kg i.v. bolus dose of theophylline from 2.56 +/- 0.37 to 1.00 +/- 0.13 ml min-1kg-1 (mean +/- SD). It is concluded that acutely administered enoxacin in a dose sufficient to inhibit the elimination of theophylline has no direct effect on theophylline neurotoxicity in rats.

Animals↗
PubMed1989

Induction of experimental thyroid dysfunction in rats with implantable pellets of thyroxine or propylthiouracil.

Subcutaneously implanted pellets containing the thyroid hormone thyroxine or the thyrotoxic agent propylthiouracil were used to induce hyper- or hypothyroidism in rats. The results obtained were compared to those produced by daily subcutaneous injection of these substances. The thyroxine pellets caused substantial elevation of serum thyroxine concentrations for at least 25 days, whereas the propylthiouracil pellets caused a pronounced decrease of serum thyroxine concentrations. Changes in heart weight and rectal temperature were consistent with the observed alterations of serum thyroxine concentrations. Treatment with propylthiouracil was associated with small elevations of serum total protein, urea nitrogen, and creatine concentrations regardless of the method of administration of this agent. It is concluded that implantable pellets are an effective and convenient means of administering drugs for producing thyroid dysfunction in rats.

Animals↗
PubMed1989

Systemic effect of ipecac on acute toxicity of phenobarbital and theophylline in rats.

The emetic agent ipecac is widely used for the initial treatment of acute oral drug overdose. Its emetic and gastric evacuative efficacies have been studied extensively but its potential for pharmacologic interactions with various drugs and other possible poisons has not been explored. The purpose of this investigation was to determine if ipecac can alter the acute toxicity of two widely used drugs that act on the central nervous system, phenobarbital and theophylline. Ipecac syrup, 5 ml/kg, was administered by gavage to male Lewis rats either 1 hr before or 15 or 30 min after the start of an iv infusion of phenobarbital or theophylline. Control animals received the syrup vehicle only. Ipecac elicited vomiting-like behavior (frequent, wide opening of the mouth) for more than 1 hr. The drug infusion was stopped immediately after onset of the loss of righting reflex (phenobarbital) or maximal seizures (theophylline). Samples of cerebrospinal fluid, blood (for serum), and the brain were obtained at that time for analysis of drug concentrations. There were no significant differences between control and ipecac-treated animals with respect to the dose requirements and drug concentrations in cerebrospinal fluid, serum, and brain at the respective pharmacologic endpoint. It is concluded that ipecac has no apparent effect on the acute toxicity of phenobarbital and theophylline in rats.

Animals↗
PubMed1989

Gender differences in the pharmacodynamics of barbiturates in rats.

There is considerable evidence of gender differences in the pharmacokinetics of numerous drugs, particularly in rodents, but very limited information concerning the effect of gender on pharmacodynamic characteristics (concentration-activity relationships). In this study, heptabarbital or phenobarbital was administered to male and female rats and the concentrations of these drugs in the brain, cerebrospinal fluid and serum at onset or offset of loss of righting reflex were determined. For heptabarbital, offset concentrations were determined in Lewis rats and onset concentrations in Wistar rats. Onset concentrations of phenobarbital were determined in Wistar rats. In all cases, the barbiturate concentrations in males were significantly lower than those in females at the pharmacologic endpoint. The biologic (serum) half-life of heptabarbital is much shorter in males (approximately 10 min) than in females (approximately 90 min) and this pharmacokinetic difference is reflected by the considerably longer duration of effect of the drug in females.

Animals↗
PubMed1989

Kinetics of drug action in disease states. XXXI. Effect of experimental hyperthyroidism on the hypnotic activity of a benzodiazepine (oxazepam) in rats.

This investigation was designed to determine the effect of experimental hyperthyroidism on the hypnotic activity of a benzodiazepine and on the binding characteristics of the benzodiazepine receptor complex. Rats were made hyperthyroid by subcutaneous implantation of slow release pellets containing L-thyroxine. This treatment produced the characteristic symptoms of hyperthyroidism: increased serum thyroxine concentrations, increased heart weight and body temperature, and decreased serum protein concentrations. The hyperthyroid rats and a parallel group of normal animals (with drug-free pellets implanted subcutaneously) were slowly infused intravenously with oxazepam until they lost their righting reflex. The hyperthyroid rats required a significantly larger dose of the benzodiazepine and their total serum and cerebrospinal fluid concentrations of oxazepam (but not the serum concentration of free drug and the brain concentration) at the onset of loss of the righting reflex were modestly but statistically significantly lower than those of the normal rats. The receptor density and affinity for diazepam in hyperthyroid rats were not significantly different from those of the normal animals. Hyperthyroidism apparently affects the pharmacokinetics of oxazepam but has, at best, only a small effect on the pharmacodynamics (hypnotic activity) of the drug.

Animals↗
PubMed1989

Monocyte/macrophage procoagulant activity as a measure of immune responsiveness in Lewis and brown Norway inbred rats. Discordance with lymphocyte proliferative assays.

In vitro lymphocyte proliferative assays were performed using Lewis (Lew) and Brown Norway (BN) rats, and compared to induction of monocyte/macrophage procoagulant activity (PCA) in a mixed lymphocyte culture and by endotoxin (LPS) (E. Coli 0111:B4). Splenic mononuclear cells from Lew rats had significantly greater mitogen-induced proliferation to concanavalin A (P = .002) and phytohemagglutinin (P = 0.007). The Lew cells also showed greater allogeneically induced proliferation by BN cells in a one-way MLC in comparison to the reciprocal BN proliferative response (P less than 0.04). PCA induction in peripheral blood mononuclear cells (PBM) by allogeneic stimulation in MLC or total content PCA by LPS did not vary significantly between the 2 strains (P greater than 0.5). Induction of PCA by LPS was rapid, with a moderate rise over basal activity at 3 hr and maximal activity at 6 hr. Two-way allogeneic induction of PCA in PBM from BN and Lew rats resulted in PCA elevation by 3 hr, which became maximal at 18 hr. One-way MLC with Lew or BN cells as responders resulted in moderate increases in PCA by 3-6 hr, with equivalent maximal activities recorded at 18 hr. Viable PCA accounted for 26-32% of total content PCA in both Lew and BN rats. Maximal allogeneic PCA induction by MLC was 14-18% of PCA induced by LPS and required a longer incubation for its expression. Our results indicate that in vitro PCA expression by Lew and BN PBM following allogeneic or endotoxin stimulation shows little interstrain variability in comparison to lymphocyte proliferative responses. Thus PCA appears to more closely reflect the observed in vivo responses of these strains to allogeneic challenge.

Animals↗