Search PubMed⌕ Search

Biomedical subjects

S K Davis

Publications and source records attributed to S K Davis.

At least 73 records · Page 4Linked to original sources
PubMed1995

Bovine fast-twitch myosin light chain 1: cloning and mRNA amount in muscle of cattle treated with clenbuterol.

The cDNA clone encoding the fast-twitch isoform of myosin light chain 1 (MLC-1f) was isolated from bovine longissimus dorsi muscle and sequenced in M13 and pUC8. An 0.8-kb subclone, produced by digestion of the cDNA with EcoRI, contained the portion of the molecule common to MLC-1f and MLC-3f. The cDNA in pUC8 contained an additional 81 bp upstream of the EcoR I digestion site, which was unique to MLC-1f. The cDNA clone was used to measure MLC-1f mRNA in longissimus dorsi muscle of cattle chronically administered the beta-adrenergic agonist clenbuterol. Treatment with clenbuterol for 50 days increased succinic dehydrogenase negative (type IIB) and positive (types I and IIA) myofiber cross-sectional areas by 25%. After the 50-day treatment period, the amount of MLC-1f mRNA was 90% greater in longissimus dorsi muscle of treated animals than in the initial group. This effect was lost when clenbuterol treatment was withdrawn for a 78-day period, during which time muscle growth in the treated animals stopped completely. We conclude that we have cloned the bovine cDNA for MLC-1f, which has provided additional evidence that beta-adrenergic agonists increase myofibrillar gene expression.

Amino Acid Sequence↗
PubMed1993

Phylogenetic relationships of pocket gophers (Cratogeomys and Pappogeomys) based on mitochondrial DNA cytochrome b sequences.

Phylogenetic relationships among 7 of the 10 species of pocket gophers in the genera Pappogeomys and Cratogeomys were addressed using nucleotide sequence data from the entire cytochrome b gene of the mitochondrial genome (1140 base pairs). Results of parsimony analysis were concordant with the results of morphological analysis (R. J. Russell, Univ. Kans. Pub. Mus. Nat. Hist. 16: 581-776, 1968), but differed somewhat from the conclusions drawn from an allozymic study of these species (R. L. Honeycutt and S. L. Williams, J. Mammal. 63: 208-217, 1982). Phylogenetic analysis indicated that Cratogeomys is monophyletic, as are the two species groups within this genus. Estimates of levels of nucleotide sequence divergence between species of these genera indicated that the cytochrome b gene of pocket gophers may have evolved at a dramatically higher rate than in organisms examined previously (D. M. Irwin, T. D. Kocher, and A. C. Wilson, J. Mol. Evol. 32: 128-144, 1991).

Amino Acid Sequence↗
PubMed1993

Estimation of genotype distributions and posterior genotype probabilities for beta-mannosidosis in Salers cattle.

beta-Mannosidosis is a lethal lysosomal storage disease inherited as an autosomal recessive in man, cattle and goats. Laboratory assay data of plasma beta-mannosidase activity represent a mixture of homozygous normal and carrier genotype distributions in a proportion determined by genotype frequency. A maximum likelihood approach employing data transformations for each genotype distribution and assuming a diallelic model of inheritance is described. Estimates of the transformation and genotype distribution parameters, gene frequency, genotype fitness and carrier probability were obtained simultaneously from a sample of 2,812 observations on U.S. purebred Salers cattle with enzyme activity, age, gender, month of pregnancy, month of testing, and parents identified. Transformations to normality were not required, estimated gene and carrier genotype frequencies of 0.074 and 0.148 were high, and the estimated relative fitness of heterozygotes was 1.36. The apparent overdominance in fitness may be due to a nonrandom sampling of progeny genotypes within families. The mean of plasma enzyme activity was higher for males than females, higher in winter months, lower in summer months and decreased with increased age. Estimates of carrier probabilities indicate that the test is most effective when animals are sampled as calves, although effectiveness of the plasma assay was less for males than females. Test effectiveness was enhanced through averaging repeated assays of enzyme activity on each animal. Our approach contributes to medical diagnostics in several ways. Rather than assume underlying normality for the distributions comprising the mixture, we estimate transformations to normality for each genotype distribution simultaneously with all other model parameters. This process also excludes potential biases due to data preadjustment for systematic effects. We also provide a method for partitioning phenotypic variation within each genotypic distribution which allows an assessment of the value of repeat measurements of the predictive variable for genotype assignment.

Animals↗
PubMed1993

Tissue-specific activity of pentose cycle oxidative enzymes during feeder lamb development.

Relationships between pentose cycle oxidative activity and differential fat growth were evaluated. Rambouillet wether lambs (n = 60) were slaughtered serially at 0, 40, 80, and 120 d on feed (15 lambs/group). Rack dissection and kidney fat weights were collected, and longissimus muscle i.m. fat content was determined. Postmortem longissimus muscle, s.c. fat, intermuscular fat (INT), and kidney fat (KP) samples were assayed in vitro for glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activity (nanomoles.minute-1.gram of tissue-1), and samples were subjected to electrophoresis (PAGE) to separate tissue-specific isoforms. Allometric coefficients for rack components indicated that s.c. fat was the earliest-maturing, slowest-growing depot, INT was the latest-maturing, fastest-growing depot, and i.m. fat was intermediate (P < .05). Kidney fat grew faster than carcass weight and, as carcass weight increased, the growth rate of KP accelerated (P < .05). Enzyme activities increased until 40 d on feed and declined thereafter. Activities differed across tissues and time on feed end points (P < .05). Ratios of G6PDH:6PGDH, reflecting flux through the oxidative phase of the pentose cycle and, therefore, lipogenic activity, suggested growth patterns similar to those indicated by allometric analysis, except in the i.m. fat depot. Development of i.m. fat initially was intermediate to KP and INT, but G6PDH:6PGDH ratios increased with time on feed, suggesting a different regulatory mechanism and maturing pattern. Multiple forms of G6PDH were detected with PAGE, and although polymorphism was not detected, a tissue-specific isoform was isolated for INT fat.

Adipose Tissue↗
PubMed1992

Variation and the phylogenetic utility of the large ribosomal subunit of mitochondrial DNA from the insect order Hymenoptera.

Nucleotide sequence variation from a 573-bp region of the mitochondrial 16S rRNA gene was determined for representative hymenopteran taxa. An overall bias in the distribution of A and T bases was observed from all taxa; however, the terebrants (parasitoids) displayed significantly lower AT ratios as well as a higher degree of strand asymmetry. Moreover, a strong positive correlation was observed between relative AT richness and sequence divergence, suggesting selection at the nucleotide level for A and T bases as well as functionality. Overall sequence difference ranged from 2.3 to 53.4%, with the maximum divergence between members of the two Hymenopteran suborders. These data were used in a phylogenetic analysis to illustrate the utility and degree of resolution provided by this information at various hierarchical levels within this taxonomically diverse order. Parsimony analysis revealed strong evidence for monophyly of the aculeates and the terebrants. Most noteworthy was a strongly supported clade containing the two terebrant superfamilies Icheumonoidea and Chalcidoidea. Conversely, high sequence divergence values resulted in instability at the base of the tree and limited resolution at the higher taxonomic levels. Nevertheless, these results do identify those taxonomic levels for which 16S rRNA sequences are phylogenetically informative.

Animals↗
PubMed1992

Effects of cocaine and norepinephrine on primary cultures of neonatal rat myocardial cells.

Sudden cardiac death associated with cocaine (Coc) abuse in healthy, physically active individuals became a grave concern in the late 1980s. It is well documented that physical activity increases circulating plasma catecholamine levels. Catecholamines as well as Coc are independently capable of inducing toxic cardiac effects. The purpose of this investigation was to evaluate the synergistic or additive toxic effects of norepinephrine (NE) and Coc in primary myocardial cell cultures obtained from 3- to 5-d-old Sprague-Dawley rats. Alterations in lactate dehydrogenase release (LDH), lysosomal neutral red retention (NR), beating activity, and morphology were evaluated after treatment of the cells for 1-24 h with 1 x 10(-3) M Coc alone, 1 x 10(-5) M Coc alone, 1 x 10(-5) M NE alone, 1 x 10(-3) M Coc with 1 x 10(-5) M NE, or 1 x 10(-5) M Coc with 1 x 10(-5) M NE. LDH release was elevated significantly after 24 h only with those cells exposed to 1 x 10(-3) M Coc alone and 1 x 10(-3) M Coc + 1 x 10(-5) M NE. Using NR retention as a score for lysosomal treatment of the cells with 1 x 10(-5) M Coc and 1 x 10(-3) M Coc alone did not decrease dye retention significantly. However, 1 x 10(-5) M NE combined with 1 x 10(-3) M Coc significantly reduced lysosomal dye retention as early as 1 h after treatment. After 24 h, 1 x 10(-5) M NE alone and 1 x 10(-5) M NE combined with 1 x 10(-5) M Coc significantly increased lysosomal fragility. Beating activity was altered in all treatment groups. Contractile activity was slow and irregular or completely absent with 1 x 10(-5) and 1 x 10(-3) M Coc, respectively. When NE (1 x 10(-5) M) was combined with both concentrations of Coc, there was distinct focalization of sharp, rapid contractions within the cells, which were asynchronous and/or arrhythmic in nature. Those cells exposed to 1 x 10(-5) M NE with 1 x 10(-5) M Coc for 24 h appeared hypercontracted with marked pseudopodia and cytoplasmic granule formation distinctly different from that exhibited by the cells exposed to 1 x 10(-5) M Coc alone. These data demonstrate that NE potentiates the adverse effects of Coc on contractile activity and morphology of spontaneously contracting neonatal myocardial cells maintained in culture.

Animals↗
PubMed1990

Chemical dependency in women: a description of its effects and outcome on adequate parenting.

The purpose of this article is to define chemical dependency in women as a maladaptive response to inadequate upbringing. A description of the situational and psychological variables that characterize chemically dependent women is offered as well as attributes these women lack that are necessary for effective parenting. The dysfunctional child-rearing patterns and the consequential outcome for the children are also described. Suggestions for clinical intervention are provided.

Child Abuse↗