PubMed Health⌕ Search

Biomedical subjects

R C Levitt

Publications and source records attributed to R C Levitt.

At least 19 recordsLinked to original sources
PubMed1992

Evidence for the localization of a malignant hyperthermia susceptibility locus (MHS2) to human chromosome 17q.

Malignant hyperthermia susceptibility is a lethal autosomal dominant disorder of skeletal muscle metabolism that is triggered by all potent inhalation anesthetic gases. Recent linkage studies suggest a genetic locus for this disorder on 19q13.1. We have previously reported three unrelated families diagnosed with MHS that are unlinked to markers surrounding this locus on 19q13.1. In this report we extend these observations and present linkage studies on 16 MHS families. Four families (25%) were found linked to the region 19q12-q13.2 (Zmax = 2.96 with the ryanodine receptor at theta = 0.0). Five families (31%) were found closely linked to the anonymous marker NME1 (previously designated NM23) on chromosome 17q11.2-q24 (Zmax = 3.26 at theta = 0.0). Two families (13%) were clearly unlinked to either of these chromosomal regions. In five additional families, data were insufficient to determine their linkage status (they were potentially linked to two or more sites). The results of our heterogeneity analyses are consistent with the hypothesis that MHS can be caused in humans by any one of at least three distinct genetic loci. Furthermore, we provide preliminary linkage data suggesting the localization of a gene in human MHS to 17q11.2-q24 (MHS2), with a gene frequency of this putative locus approximately equal to that of the MHS1 locus on 19q.

Adult↗
PubMed1992

Prospects for the diagnosis of malignant hyperthermia susceptibility using molecular genetic approaches.

MHS is a heterogeneous pharmacogenetic disorder in the human that is likely to be caused by one of a variety of genetic defects, in one of a number of genes. Direct molecular methods will provide a rapid, efficient, non-invasive, and low-cost screening test once the causative genetic mutations have been identified. However, until this objective is met, indirect molecular genetic methods can be used to demonstrate the inheritance of an abnormal gene in certain family members at risk. This requires localizing the gene that produces the abnormal phenotype to a subchromosomal segment by linkage analysis and showing the coinheritance of MHS and DNA markers in a number of family members. Indirect molecular genetic methods are likely to be particularly useful in the diagnostic evaluation of children too small to be biopsied in families where others have been biopsied or their phenotypes are known. It appears likely that molecular genetic methods will not eliminate the usefulness of the muscle biopsy and caffeine-halothane contracture test in the near future. Rather, these diagnostic tests will complement one another and significantly improve our understanding of the complexity of this disorder.

Base Sequence↗
PubMed1992

Atopy and bronchial hyperresponsiveness: exclusion of linkage to markers on chromosomes 11q and 6p.

Previous studies have reported a familial predisposition for the development of atopy, bronchial hyperresponsiveness and clinical asthma, and therefore have suggested the presence of a heritable component to these disorders. The specific contributions of genetic and environmental factors in the pathogenesis of allergic disease and asthma have not been determined although Cookson et al. [1] have postulated linkage between atopy and chromosome 11q. We have studied 20 families (two and three generations) ascertained through a proband identified as having asthma (90% were also allergic) during the period of time between 1962 and 1970. Of those who were originally skin test positive, 82% remained positive. All probands whose pulmonary function allowed retesting (FEV1 > 1.2 l) remained hyperresponsive to histamine. The children of these probands are now in the same age range as their parents when they were originally evaluated; 66% are atopic using criteria described by Cookson et al. (one or more positive skin tests > or = 2 mm, an elevated total serum IgE or a positive specific IgE) and 22% demonstrate bronchial hyperresponsiveness (PC20 FEV1) to histamine. Using the highly polymorphic marker INT2 (which maps 2 cM from p lambda MS.5 l on chromosome 11q) and atopy, we obtained a lod score of -2.00 at a recombination fraction of 0.12. In addition, because many studies have suggested an association between atopy and certain HLA antigens, we investigated the possibility of linkage between atopy and bronchial hyperresponsiveness and D6S105, a polymorphic marker on chromosome 6p, located 7 cM from HLA-DR. For this marker and atopy, we observed a lod score of -2.00 with a recombination fraction of 0.07.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Evidence for genetic heterogeneity in malignant hyperthermia susceptibility.

Malignant hyperthermia susceptibility (MHS) is a clinically heterogeneous pharmacogenetic disorder characterized by accelerated metabolism, hyperthermia, and frequently muscle rigidity. MHS is elicited by all commonly used potent inhalation anesthetics and depolarizing neuromuscular blockers and remains an important cause of death due to anesthesia. Recent linkage studies suggest a single genetic locus for this disorder on chromosome 19q13.1. The results of our linkage analyses exclude several loci on 19q13.1 as a site for the gene(s) that produces the MHS phenotype in three unrelated families and clearly establish genetic heterogeneity in this disorder. These results are consistent with the hypothesis that the genetic defect that alters thermoregulation may vary in MHS and that clinical variability in the expression of MHS may be explained by genetic heterogeneity.

Chromosomes, Human, Pair 19↗
PubMed1991

Polymorphisms in the transcribed 3' untranslated region of eukaryotic genes.

In this review we present preliminary evidence for a new class of polymorphism that may be used in a systematic way to map cDNAs efficiently and to expedite the construction of a high-resolution genetic map of the human genome. Ultimately, transcribed 3' untranslated polymorphisms will warrant further study because they should be widely distributed throughout the genome within transcribed sequences, and they can be readily identified as a result of cDNA cloning and sequencing. Furthermore, these markers should be universally available on the basis of the sequence data and highly useful in linkage analyses.

Chromosome Mapping↗
PubMed1990

Gene candidate.

Explore the source record for details and available documents.

Chromosomes, Human, Pair 19↗
PubMed1990

A genetic approach to the study of lung physiology: understanding biological variability in airway responsiveness.

Genetic techniques are generally applicable to almost any trait or physiological process for which biological variability can be demonstrated. These methods have not commonly been applied to studies on lung pathophysiology, however. The aim of this commentary will be to introduce and discuss the potential application of genetic methods to research on the pathophysiology of asthma. Recent efforts to identify genes that determine airway hyperresponsiveness in the genetically standardized inbred laboratory mouse will be reviewed. These experiments demonstrate how genetic background influences the expression of airway responsiveness to certain environmental stimuli and illustrate the application of selected genetic resources. A discussion follows on how these genetic models may potentially provide insight into asthma and our understanding of the molecular physiology and genetic regulation of airway hyperreactivity to various stimuli.

Animals↗
PubMed1990

A genetic model for evaluation of susceptibility to ozone-induced inflammation.

We examined ozone-induced airway inflammatory responses in inbred mice, and progeny of crosses between them, to investigate genetic susceptibility to ozone. Nine strains of male mice (18-23 g, 5-7 wk) were exposed for 3 h to 2 ppm ozone (O3) or filtered air (control), and pulmonary inflammation was assessed 2, 6, and 24 h after exposure by inflammatory cell counts and total protein content in bronchoalveolar lavage (BAL). The time course of the response to O3 was consistent between the strains. The maximum change in polymorphonuclear leukocytes (PMNs) was detected 6 h after O3, and the maximum increase in BAL protein occurred 24 h postexposure. Air controls exhibited no detectable changes in the parameters of inflammation at any time. The phenotypes of the C57BL/6J (B6, termed susceptible) and C3H/HeJ (C3, termed resistant) strains were easily distinguished by the magnitude of their inflammatory responses to O3. A 22-fold difference in PMNs was detected between the two strains 2 h after O3 (P less than 0.001), and a sixfold difference was found 6 h after O3 (P less than 0.001). Total BAL proteins were also significantly different between the B6 and C3 strains 6 h (P less than 0.01) and 24 h after O3 (P less than 0.001). To further evaluate the potential genetic contribution to the inflammatory response, the F1, F2, and backcross progeny from crosses between B6 and C3 strains were examined. The phenotypes of these progeny were consistent with the hypothesis that a single autosomal recessive gene at the Inf locus confers susceptibility to acute O3-induced influx of PMNs, but the genetic control of altered permeability is not clear.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

In vitro tracheal responses from mice chosen for in vivo lung cholinergic sensitivity.

We selected two inbred strains of mice based on their different in vivo lung responses to intravenous acetylcholine for studies on the in vitro tracheal responses to contractile and relaxing agents. In addition, we studied the role of cyclooxygenase products on the in vitro responses. Tracheal rings were contracted with increasing concentrations of carbachol and KCl and relaxed with increasing concentrations of isoproterenol after contraction with carbachol at the concentration that produced 30, 50, and 70% of the maximal contraction (EC30, EC50, and EC70, respectively) and KCl at the EC50. Half the tracheae simultaneously underwent the same protocols after pretreatment with indomethacin (3 X 10(-6) M). Despite a severalfold difference in the maximal response to cholinergic agents in vivo, there were no significant differences between the strains in the tracheal responses to carbachol (P = 0.78) or KCl (P = 0.13) in vitro. Both strains showed inhibition of the isoproterenol relaxation by carbachol (P less than 0.0001). Multiple linear regression analysis showed that the strain that was more sensitive to carbachol in vivo was also more sensitive to isoproterenol in vitro after carbachol contraction (P = 0.014). The greater isoproterenol sensitivity of the tracheae from this strain was not present after contraction with KCl, nor were these tracheae more sensitive to relaxation with sodium nitroprusside. Indomethacin pretreatment of the tissues in vitro augmented the maximal response and the sensitivity to carbachol (P less than 0.001) and KCl (P = 0.0006), and this effect was similar in both strains. Evaluation of isoproterenol relaxation after indomethacin pretreatment was confounded by the lower concentrations of carbachol needed for contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1990

Succinylcholine potentiates responses to intravenous acetylcholine in the canine lung periphery.

Using the wedged bronchoscope technique to measure collateral resistance (Rcs), we evaluated the effect of succinylcholine (SCh) on the response to acetylcholine (ACh) and methacholine (MCh) in the lung periphery in six mongrel dogs. Dogs were anesthetized, intubated, and mechanically ventilated. After a stable baseline Rcs was obtained, responses to intravenous ACh (25-200 micrograms), intravenous MCh (3-30 micrograms), and aerosolized ACh (30-100 micrograms/ml for 15 s) were measured. We compared the Rcs responses with 1) ACh alone, 2) ACh 2 min after SCh (0.5 mg/kg), 3) ACh 2 min after SCh and during hexamethonium infusion (5 mg/kg + 10 mg.kg-1.h-1), 4) MCh 2 min after SCh, and 5) ACh aerosol 2 min after SCh. SCh did not significantly alter baseline airway tone. SCh increased the Rcs response to ACh by 48 +/- 17% (SE) (P less than 0.01). SCh in the presence of hexamethonium increased the Rcs response by 10 +/- 3% (P less than 0.05), while hexamethonium itself increased the response to ACh by 69 +/- 27%. Because SCh did not increase the Rcs response to intravenous MCh or to aerosolized ACh, SCh probably enhances airway reactivity to intravenous ACh by competing for pseudocholinesterase in plasma. We conclude that the level of muscle relaxant must be taken into account in interpreting studies of airway reactivity when intravenous ACh is employed.

Acetylcholine↗
PubMed1989

Autosomal recessive inheritance of airway hyperreactivity to 5-hydroxytryptamine.

We have previously reported that airway hyperresponsiveness to acetylcholine (ACh) is inherited as an autosomal recessive trait in A/J and C3H/HeJ mice and the progeny of crosses between them (FASEB J. 2: 2605-2608, 1988). In the present report, we have extended these studies by evaluating the biological variability in the airway response to 5-hydroxytryptamine (5-HT) and ACh among multiple genetically standardized inbred strains of mice. The pattern of airway responsiveness to ACh differed significantly from that of 5-HT in nine inbred strains of mice. A/J mice showed nonspecific airway hyperresponsiveness to both 5-HT and ACh. DBA/2J mice were hyperresponsive to 5-HT but not to ACh. An airway phenotype that resembled these inbred strains is termed HYPERREACTIVE. The C3H/HeJ and C57BL/6J inbred strains were minimally reactive to either ACh or 5-HT. Airway phenotypes that resembled these minimally reactive strains are termed HYPOREACTIVE. The frequency of HYPERRACTIVE and HYPOREACTIVE offspring from crosses between A/J and C3H/HeJ mice or DBA/2J and C57BL/6J mice is consistent with a single autosomal recessive gene, primarily determining airway hyperresponsiveness to 5-HT. We report linkage studies which suggest that these genes are not closely linked and that 5-HT and ACh airway hyperresponsiveness is inherited independently. The results of these studies suggest that murine nonspecific airway hyperresponsiveness is determined by multiple genes.

Acetylcholine↗
PubMed1988

Expression of airway hyperreactivity to acetylcholine as a simple autosomal recessive trait in mice.

An increased airway response to various bronchoconstricting agents is one of the hallmarks of asthma. An interdependence of heredity and environment appears to determine this nonspecific hyperreactivity of the airways. The present study describes the patterns of inheritance of the airway response to a direct mediator of smooth muscle contraction (acetylcholine) in A/J and C3H/HeJ inbred mice and their offspring. The mean airway response to acetylcholine was greater than sixfold higher in A/J mice as compared with C3H/HeJ mice. Two phenotypes were easily distinguished on the basis of airway responses to acetylcholine in the progeny of A/J and C3H/HeJ mice. These two phenotypes were termed HYPERREACTIVE (after the A/J strain) and HYPOREACTIVE (after the C3H/HeJ strain). The observed frequencies of HYPERREACTIVE and HYPOREACTIVE phenotypes in the (A/J x C3H/HeJ) F1; (C3H/HeJ x A/J) F1 x C3H/HeJ (C3H/HeJ backcross); and the [(A/J x C3H/HeJ) F1 x (C3H/HeJ x A/J) F1] F2 are consistent with a single autosomal recessive gene primarily controlling acetylcholine-mediated airway responses. This single gene difference in airway response is completely inhibited by atropine and therefore mediated entirely by the muscarinic acetylcholine receptor.

Acetylcholine↗
PubMed1984

Effects of cimetidine on theophylline, acetaminophen, and zoxazolamine toxicity in the intact mouse.

3-Methylcholanthrene treatment of C57BL/6N mice induces significant amounts of cytochromes P1-450, whereas P1-450 levels in 3-methylcholanthrene-treated DBA/2N mice are no different from those in control C57BL/6N or DBA/2N mice. Comparison of 3-methylcholanthrene-treated C57BL/6N and DBA/2N mice thus provides a convenient means of determining the role of P1-450 metabolism in two strains of mice following identical drug treatment regimens. 3-Methylcholanthrene-induced P1-450 is shown to be more effective than other forms of P-450 in detoxifying theophylline and zoxazolamine and in enhancing the toxicity of acetaminophen. Cimetidine in vivo blocks these metabolic pathways, resulting in increased toxicity of theophylline and zoxazolamine and protection against acetaminophen toxicity. These data illustrate the double-edged sword nature of P1-450 metabolism and the possibility of a paradoxical effect of cimetidine during drug-drug interactions in vivo. Cimetidine is shown to inhibit in vivo and in vitro the metabolism by both 3-methylcholanthrene-induced P1-450 and control forms of P-450; these data suggest that cimetidine may be acting at the level of P-450 reduction by NADPH-P-450 oxidoreductase. This same mechanism of action has been previously suggested for ellipticine.

Acetaminophen↗
PubMed1983

Screening of 16 common therapeutic drugs. Possible association with the Ah locus.

16 common therapeutic agents were screened for differences in sedation or lethality between C57BL/6N and DBA/2N inbred mouse strains that had been previously treated with beta-naphthoflavone. No differences were observed for meprobamate, valium, promethazine, valproic acid, lincomycin, imipramine, terbutaline, propoxyphene, nitrofurantoin, amphotericin B, or diphenhydramine. C57BL/6N mice appeared to be more resistant than DBA/2N mice to the lethal effects of isoxsuprine, niridazole, pentazocine, isoniazid, and hydralazine. None of these latter five drugs had any capacity to displace [3H-1,6]2,3,7,8-tetrachlorodibenzo-p-dioxin from the liver cytosolic Ah receptor in C57BL/6N mice. With the use of beta-naphthoflavone-pretreated offspring from the (C57BL/6N) (DBA/2N)F1 X DBA/2N backcross, a strict correlation (100% of 24 individuals in each case) was found between the Ahb allele and resistance to the lethal effects of isoxsuprine or niridazole. No correlation between the Ah locus and pentazocine, hydralazine, or isoniazid lethality was apparent. These results indicate that presence of the Ahb allele is associated with increased protection against isoxsuprine and niridazole lethality. This increased protection may reflect enhanced detoxication metabolic pathways (e.g., induced cytochrome P1-450 and/or uridine diphosphate glucuronosyltransferase controlled by the Ah locus). The increased protection is not related to interaction of these drugs with the Ah receptor. It should be kept in mind that gene-environment interactions involving the Ah locus and isoxsuprine or niridazole may be important in certain clinical instances.

Animals↗