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Biomedical subjects

R K Smith

Publications and source records attributed to R K Smith.

At least 37 records · Page 2Linked to original sources
PubMed1999

Should equine athletes commence training during skeletal development?: changes in tendon matrix associated with development, ageing, function and exercise.

In human athletes, conditioning, training and competition are commenced before skeletal maturity. Yet in equine athletics, racing of young (age 2 years) horses remains contentious. Tendon injury persists as major causes of wastage in equine athletes. Minimising injury and associated welfare issues could involve a radical approach to the timing and implementation of conditioning and training. Tendons were examined from Thoroughbreds, Dutch Warmblood foals, working horses and also a group of wild horses to evaluate effects of age, function and exercise. Gross mechanical properties did not differ significantly with age or exercise, but showed a high variance within each group. Mechanical properties of tendon tissue showed significant differences as a function of age and location. The collagen fibril crimp angle and length showed a regional reduction in the central core with exercise and age, with a synergistic effect. Regional differences in collagen fibril diameter were seen in long-term exercised older horses, but not in short-term exercised, or younger, horses. The higher proportion of small fibrils in the central region of the long-term exercised horses did not correlate with new collagen formation and therefore appear to result from disassembly of the larger diameter fibrils. Fibril diameter distributions were influenced by exercise regimens in the growing foal. Changes in molecular composition occurred in longer-term exercise and older horses, in the centre of the tendon, with higher levels of type III collagen and changes in glycosaminoglycan (GAG) content. Cartilage Oligomeric Matrix Protein (COMP) levels also appear to be modulated by age, function and superimposition of exercise. These changes were all exacerbated with age and exercise, suggesting appropriate exercise in young horses may lead to a lower incidence of injury than in older horses. An hypothesis is advanced that immature tendon can respond to exercise while mature tendon has limited, if any, ability to do so. These findings support potentially controversial earlier conditioning and racing of younger, rather than older, equine athletes.

Aging↗
PubMed1999

Treadmill exercise-induced tendon hypertrophy: assessment of tendons with different mechanical functions.

The equine superficial digital flexor tendon (SDFT) functions as an energy store during high-speed gaits reducing the energetic cost of locomotion. To enable the SDFT to function effectively, the appropriate mechanical properties are essential. We tested the hypothesis that the SDFT does not undergo gross hypertrophy in response to high-intensity exercise whereas tendons not involved in energy storage undergo adaptive hypertrophy. Two groups (n = 6) of Thoroughbred fillies were trained at high-intensity on a high-speed equine treadmill for 5 months (short-term study) or 18 months (long-term study). Age-matched groups (n = 6) of horses undertook low-intensity exercise only for the same time period. Throughout the short-term study the SDFT and deep digital flexor tendon (DDFT) were ultrasonograpically scanned at mid-metacarpal level and cross-sectional area (CSA) calculated. At the end of the short-term study (horse age = 2 years) and long-term study (horse age = 3 years) the left SDFT, DDFT, suspensory ligament (SL) and common digital extensor tendon (CDET) were harvested and CSA calculated. Comparison of the DDFT from 2- and 3-year-old horses revealed an age-related increase in CSA which was confirmed by ultrasonographs. Post mortem analysis showed a significant hypertrophy of the CDET with high-intensity training in the short-term study (younger horses). CSA did not differ significantly between training groups for any of the structures following long-term training. These results suggest a structure specific hypertrophic response to the imposed training regime.

Animals↗
PubMed1999

Age-related changes and effect of exercise on the molecular composition of immature equine superficial digital flexor tendons.

To test the hypothesis that exercise at very young age may influence the eventual molecular composition (and hence the biomechanical properties) of tendon tissue in the horse, 43 Dutch Warmblood foals were allotted to 3 differently exercised groups (box-rest, box-rest with training and pasture exercise). Twenty-four superficial digital flexor tendons (SDFTs) were collected at age 5 months (8 from each exercise group) and the others were obtained at 11 months after an additional period of light exercise that was equal for all remaining foals and was intended to see if any induced changes would be reversible or not. Significant changes in DNA content (cellularity), hyaluronic acid (HA) and polysulphated glycosaminoglycans (PSGAGs) were found after the 5 month period of different exercise regimens. There was a tendency towards an exercise-related effect on hydroxylysine content and number of hydroxylysylpyridinoline (HP) crosslinks. Levels of Cartilage Oligomeric Matrix Protein (COMP), measured by homologous inhibition ELISA, showed significant differences at 5 months and were highest in foals kept at pasture and lowest in foals maintained in a box but given enforced exercise. At 11 months, the biochemical parameters of the tendons from the foals of the former box-rest and pasture groups became similar, indicating the capacity of the immature tendon to recover from a retarded development. However, the ratio of PSGAGs per unit of DNA of the former training group was significantly lower than those from the other groups, suggesting that the training regimen in this study had a lasting negative effect on the tenocytes resulting in a decrease of the production of PSGAGs. Therefore, inappropriate or excessive exercise may damage developing tendon, with limited recovery after normalising the exercise level. These possibly deleterious effects of a training regimen on tendon development may be important for the management of young would-be equine athletes.

Analysis of Variance↗
PubMed1997

The distribution of cartilage oligomeric matrix protein (COMP) in tendon and its variation with tendon site, age and load.

A protein prominent in guanidine hydrochloride extracts of adult bovine and equine digital flexor tendons was confirmed to be Cartilage Oligomeric Matrix Protein (COMP) by non-reducing and reducing SDS-PAGE, reaction with rabbit anti-COMP polyclonal antiserum on Western blots, trypsin digestion followed by HPLC on a C2/C18 column, and identification of COMP mRNA from tendon on Northern blots. Immunohistochemistry and Western blots of extracts showed COMP to be present in all regions of digital flexor tendons. Equine tendon COMP was purified by ion exchange chromatography and gel filtration and used in a heterologous inhibition ELISA to quantify COMP in equine digital flexor tendons at different ages, and in other tendons and ligaments. Mean COMP levels in digital flexor tendon were approximately 2-5mg/g wet weight, but they showed a large variation. Levels were low in neonatal tendon but rose rapidly during growth, with the metacarpal (tensional) superficial digital flexor tendon having the highest levels (approximately 10mg/g wet weight). Levels subsequently declined in this region, while in areas which experience a variable amount of compression, levels increased less but then remained constant. Extensor tendons and collateral ligaments, which experience less loading in vivo, had levels similar to those in neonatal tendon. COMP was identified in scarred skin and granulation tissue but not in normal skin, chronic fibrosis, or a fibrosarcomatous skin growth. A unilateral non-weight-bearing growing animal contained three to six times more COMP in the weight-bearing digital flexor tendons compared to the paralyzed limb, while the extensor tendons had similar amounts in both limbs. With the recent discovery of a COMP gene mutation causing pseudoachondroplasia (Hecht et al., 1995), in which lax tendons and ligaments are a feature, the present data suggest that COMP is synthesized in response to, and is necessary for tendon to resist, load.

Aging↗
PubMed1997

Overexpression of glutathione S-transferase/glutathione peroxidase enhances the growth of transgenic tobacco seedlings during stress.

Transgenic tobacco seedlings that overexpress a cDNA encoding an enzyme with both glutathione S-transferase (GST) and glutathione peroxidase (GPX) activity had GST- and GPX-specific activities approximately twofold higher than wild-type seedlings. These GST/GPX overexpressing seedlings grew significantly faster than control seedlings when exposed to chilling or salt stress. During chilling stress, levels of oxidized glutathione (GSSG) were significantly higher in transgenic seedlings than in wild-types. Growth of wild-type seedlings was accelerated by treatment with GSSG, while treatment with reduced glutathione or other sulfhydryl-reducing agents inhibited growth. Therefore, overexpression of GST/GPX can stimulate seedling growth under chilling and salt stress, and this effect could be caused by oxidation of the glutathione pool.

Agriculture↗
PubMed1996

A novel role for the integrin-binding III-10 module in fibronectin matrix assembly.

Fibronectin matrix assembly is a cell-dependent process which is upregulated in tissues at various times during development and wound repair to support the functions of cell adhesion, migration, and differentiation. Previous studies have demonstrated that the alpha 5 beta 1 integrin and fibronectin's amino terminus and III-1 module are important in fibronectin polymerization. We have recently shown that fibronectin's III-1 module contains a conformationally sensitive binding site for fibronectin's amino terminus (Hocking, D.C., J. Sottile, and P.J. McKeown-Longo. 1994. J. Biol. Chem. 269: 19183-19191). The present study was undertaken to define the relationship between the alpha 5 beta 1 integrin and fibronectin polymerization. Solid phase binding assays using recombinant III-10 and III-1 modules of human plasma fibronectin indicated that the III-10 module contains a conformation-dependent binding site for the III-1 module of fibronectin. Unfolded III-10 could support the formation of a ternary complex containing both III-1 and the amino-terminal 70-kD fragment, suggesting that the III-1 module can support the simultaneous binding of III-10 and 70 kD. Both unfolded III-10 and unfolded III-1 could support fibronectin binding, but only III-10 could promote the formation of disulfide-bonded multimers of fibronectin in the absence of cells. III-10-dependent multimer formation was inhibited by both the anti-III-1 monoclonal antibody, 9D2, and amino-terminal fragments of fibronectin. A fragment of III-10, termed III-10/A, was able to block matrix assembly in fibroblast monolayers. Similar results were obtained using the III-10A/RGE fragment, in which the RGD site had been mutated to RGE, indicating that III-I0/A was blocking matrix assembly by a mechanism distinct from disruption of integrin binding. Texas red-conjugated recombinant III-1,2 localized to beta 1-containing sites of focal adhesions on cells plated on fibronectin or the III-9,10 modules of fibronectin. Monoclonal antibodies against the III-1 or the III-9,10 modules of fibronectin blocked binding of III-1,2 to cells without disrupting focal adhesions. These data suggest that a role of the alpha 5 beta 1 integrin in matrix assembly is to regulate a series of sequential self-interactions which result in the polymerization of fibronectin.

Amino Acid Sequence↗
PubMed1996

Ultrasonography of the equine triceps muscle before and after general anaesthesia and in post anaesthetic myopathy.

The ultrasonographic appearance of the equine triceps muscle of clinically normal horses, before and after general anaesthesia, was investigated and compared with 5 cases of post anaesthetic myopathy. The triceps muscle areas were examined bilaterally using a 7.5 MHz linear array probe in 2 different planes, with each limb both weightbearing and nonweightbearing. The triceps muscles of 4 unanaesthetised horses were scanned twice, 24 h apart. Six horses underwent general anaesthesia and were scanned pre-anaesthesia and at 1 and 24 h intervals after recovery. Blood samples were obtained in the unanaesthetised group at each scan time and, in the anaesthetised group, pre-anaesthesia and at 10 min, 5 and 24 h after recovery. Creatine kinase (CK) and aspartate aminotransferase (AST) concentrations were measured. Anaesthetic details and recovery were related to the ultrasonographic and muscle enzyme findings. Five horses with post anaesthetic myopathy were scanned at intervals after the onset of clinical signs. In normal horses, the triceps muscle appeared ultrasonographically as echoic striations separated by anechoic areas. The fascia dividing muscle bellies was visible as an echoic line. Ultrasonographs obtained with the limb nonweightbearing had no change or a slight overall increase in echogenicity. The scans of control unanaesthetised horses were unchanged on successive days. All anaesthetised horses had uncomplicated anaesthesia and recoveries and did not exhibit any clinical signs of post anaesthetic myopathy. Elevated CK and AST values were found up to 342 and 195%, respectively, of the pre-anaesthetic values but no significant alterations in the ultrasonographic appearance of the muscles were detected. Clinical cases of post anaesthetic myopathy had disruption of the normal ultrasonographic pattern. There was an overall increase in echogenicity with a loss of the normal striated pattern. In 3 cases, there was localised increased echogenicity within the muscle. One of these horses was humanely destroyed for other reasons and histological examination of the affected muscle revealed a necrotic area correlating with the hyperechoic region. Two horses had bilateral involvement of the triceps musculature. Four horses recovered clinically from the myopathy and the ultrasonographic appearance returned to normal except in 1 horse where focal hyperechoic regions remained 10 weeks after the onset of the clinical signs.

Anesthesia Recovery Period↗
PubMed1996

Relationships between polymorphism for mitochondrial deoxyribonucleic acid and yield traits of Holstein cows.

Two independent data files from the breeding herd of Iowa State University and six North Carolina herds were used to examine relationships between yield traits and mtDNA polymorphism. Maternal lineages were established by tracing ancestry of cows to founder females in the herd book of the Holstein Association. Data from Iowa State University were 1476 records from 602 cows from 29 maternal lineages. The nucleotides of mtDNA encoding rRNA were sequenced. Eleven sites of polymorphism were found. An animal model for gene substitution was used to examine the relationship between sequence differences and yield traits. Traits analyzed were mature equivalent yield of milk, fat, SNF, and milk energy as well as concentrations of fat, SNF, and milk energy. Effects of sequence differences were significant for most traits. Sequence information from the D-loop was available for 12 lineages from North Carolina. The effect of polymorphism at 4 sites was examined using 1472 records from 668 cows. Traits measured were the same, except that protein replaced SNF. No significant relationships existed between any of the traits and D-loop polymorphism, but results suggested that an association might exist between polymorphism and concentrations of milk yield, fat percentage, and energy. Whenever a significant relationship was detected, the effect of mutation (rare genotype) was detrimental.

Animals↗
PubMed1995

Propofol infusion technique for outpatient general anesthesia.

PURPOSE: The purpose was to evaluate the suitability of a continuous propofol infusion in combination with alfentanil for outpatient general anesthesia in an oral and maxillofacial surgery practice. MATERIALS AND METHODS: Twenty-seven ASA 1 patients were selected to undergo oral and maxillofacial surgery outpatient procedures of short duration. Induction of anesthesia was accomplished with 1 mg/kg intravenous (i.v.) propofol and 10 micrograms/kg i.v. alfentanil. Local anesthesia was administered. General anesthesia was maintained with a continuous infusion of 150 micrograms/kg/min of propofol. Various physical and psychomotor responses were recorded during induction, maintenance, emergence, and recovery. RESULTS: Anesthesia was successfully induced in all patients with single, slowly titrated, bolus doses of 1 mg/kg of propofol and 10 micrograms/kg of alfentanil. Induction of general anesthesia occurred in less than 1 minute in all cases and no excitatory phenomena, tremor, or hypertonus were observed. Maintenance of anesthesia was adequately accomplished and cardiovascular parameters remained within acceptable limits throughout the procedure. The average length of surgery was 22 minutes. Movement to surgical stimulus was minimal and easily managed with additional local anesthetic and/or a 10-mg bolus of propofol. Time to eye opening was approximately 5 minutes from the discontinuation of the propofol infusion. No emergence phenomena were observed. All patients were ready for discharge with baseline psychomotor activity within 30 minutes following the end of the procedure. The average total dose of propofol was 350 mg and the average dose of alfentanil was 750 micrograms. CONCLUSION: This anesthetic technique has numerous advantages with minimal side effects, and should be considered for routine use for outpatient general anesthesia in oral and maxillofacial surgery.

Adolescent↗
PubMed1994

The cross-sectional areas of normal equine digital flexor tendons determined ultrasonographically.

Fifty-two animals, comprising 22 Irish Draught crosses (Group A), 15 Thoroughbreds (Group B) and 15 ponies (Group C) were examined ultrasonographically using a 7.5 mHz linear array probe and stand-off pad. All animals were free of tendon disease as determined from clinical and ultrasonographical examination. The superficial (SDFT) and deep (DDFT) digital flexor tendons were scanned at 7 transverse (axial) levels between the carpus and metacarpophalangeal joint. Each transverse image was digitised using a commercially available frame grabber and the cross-sectional areas of each tendon at each level measured using a dedicated software application. Excellent accuracy (averaging less than 5%) was demonstrated between the ultrasound generated areas and those measured from the tendons post mortem in 12 limbs. The mean, s.d. and tolerance intervals of both SDFT and DDFT cross-sectional areas at each level were determined for each group of horses. There was no statistically significant difference between Groups A and B and these 2 groups were, therefore, combined for further analysis. The cross-sectional areas of both tendons were statistically smaller for Group C when compared to Groups A and B. The ratio of SDFT to DDFT cross-sectional areas was calculated for each level and this demonstrated less variation between groups. The difference in measurements between limbs of the same horse was analysed. The mean differences for all groups were 9.13 mm2 for the SDFT and 11.64 mm2 for the DDFT. Upper limits (95% of the population) were 22.67 mm2 (SDFT) and 29.22 mm2 (DDFT).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Mutations of the intronic IgH enhancer and its flanking sequences differentially affect accessibility of the JH locus.

To investigate the role of intronic immunoglobulin heavy chain (IgH) enhancer (E mu) in generating accessibility of the JH locus for VDJ recombination, we generated ES cells in which E mu or its flanking sequences were mutated by replacement with or insertion of an expressed neor gene. Heterozygous mutant ES cells were used to generate chimeric mice from which pre-B cell lines were derived by transformation of bone marrow cells with Abelson murine leukemia virus (A-MuLV). Comparison of the rearrangement status of the normal and mutated alleles in individual pre-B cell lines allowed us to assay for cis-acting effects of the mutations. Replacement of a 700 bp region immediately downstream from the core E mu [which includes part of the 3' matrix associated region (MAR) and the I mu exon] had no obvious effect on rearrangement of the targeted allele, indicating that insertion of a transcribed neor gene into the JH-C mu intron does not affect JH accessibility. In contrast, replacement of an overlapping 1 kb DNA fragment that contains the E mu resulted in a dramatic cis-acting inhibition of rearrangement, demethylation and germline transcription of the associated JH locus. Surprisingly, insertion of the neor gene into the 5' MAR sequence approximately 100 bp upstream of the core E mu also dramatically decreased recombination of the linked JH locus; but, in many lines, did not prevent demethylation of this locus. We conclude that integrity of the E mu and upstream flanking sequences is required for efficient rearrangement of the JH locus and that demethylation of this locus, per se, does not necessarily make it a good substrate for VDJ recombination.

Animals↗
PubMed1992

Elevated levels of midtrimester maternal serum alpha-fetoprotein are associated with preterm delivery but not with fetal growth retardation.

OBJECTIVE: Our objective was to determine if the low birth weight associated with unexplained elevations of midtrimester maternal serum alpha-fetoprotein levels is due to prematurity or to fetal growth retardation. STUDY DESIGN: Rates of preterm delivery and fetal growth retardation were analyzed according to incremental maternal serum alpha-fetoprotein levels in 5555 women, predominantly white, who were screened for neural tube defects (group 1) and 843 women, predominantly black, with risk factors for low birth weight (group 2). Statistical methods included chi 2, t tests, analysis of variance, and regression analysis. RESULTS: In both groups increasing levels of maternal serum alpha-fetoprotein are significantly associated with preterm delivery but not with fetal growth retardation. The preterm delivery rate increased in each group from 8% at levels less than 0.5 multiples of the median to 18.1% (p less than 0.001) at levels greater than or equal to 2.5 multiples of the median in group 1 and 28.1% (p = 0.01) in group 2. CONCLUSIONS: Women with unexplained elevations of maternal serum alpha-fetoprotein are at increased risk for preterm delivery but not fetal growth retardation. Because of the wide availability of maternal serum alpha-fetoprotein screening, women at increased risk for preterm delivery can be identified in the midtrimester of pregnancy.

Black People↗
PubMed1992

Transcriptional down-regulation of N-myc expression during B-cell development.

We have used nuclear run-on and DNase I sensitivity analyses to study the activity of the N-myc genes in cell lines that represent different stages of B-cell development. Both transformed pre-B-cell lines and a nontransformed pre-B-cell clone transcribe the N- and c-myc genes at substantial levels; in the nontransformed clone, transcription of these genes is regulated by the pre-B-cell growth factor interleukin-7. In contrast, transformed cell lines that represent the more mature stages of the B-cell pathway and mitogen-stimulated normal splenic B lymphocytes express the c-myc gene but do not express the N-myc gene at detectable levels. Down-regulation of N-myc expression in these cells occurs at the level of transcriptional initiation. Correspondingly, a set of DNase I-hypersensitive sites present in the 5' region of the N-myc promoter of pre-B-cell lines are absent in B-cell lines. To further elucidate this process, we have constructed fusion cell lines between an N-myc-expressing pre-B-cell line and a nonexpressing myeloma line; the hybrid cell lines transcriptionally down-regulate the pre-B copies of the N-myc gene. Lack of N-myc expression in a number of nonlymphoid cell lines also resulted from lack of N-myc transcription. Together, our findings demonstrate that the down-regulation of N-myc expression in the later stages of B-cell development is mediated primarily at the level of transcriptional initiation. They further show that dominant, trans-acting factors present in more mature B-lineage cell lines act to down-regulate the transcription of N-myc.

Animals↗
PubMed1992

Better planning needed to strengthen patient-care systems.

The word "change" is on everyone's lips this year. The desire for change in patient-care information applications is very strong, too, according to a recent Computers in Healthcare patient-care systems survey. Three nursing executives have studied the CIH survey results and give their view on why strategic planning for patient-care systems is so poor when the desire for these applications is so great.

Attitude of Health Personnel↗
PubMed1991

Mechanism of endogenous myc gene down-regulation in E mu-N-myc tumors.

Transgenic mouse lines carrying the N-myc oncogene deregulated by the immunoglobulin heavy-chain enhancer spontaneously develop B-lymphoid tumors (R. Dildrop, A. Ma, K. Zimmerman, E. Hsu, A. Tesfaye, R. DePinho, and F. W. Alt, EMBO J. 8:1121-1128, 1989; H. Rosenbaum, E. Webb, J. M. Adams, S. Cory, and A. W. Harris, EMBO J. 8:749-755). Permanent cell lines derived from these tumors (E mu-N-myc cell lines) express extremely high levels of the N-myc transgene but little or no detectable endogenous N-myc or c-myc. We have employed nuclear run-on assays to show that down-regulation of endogenous N- and c-myc expression occurs at the transcriptional level. To determine whether the lack of endogenous myc gene transcription is a direct effect of high-level N-myc transgene expression, we have generated Abelson murine leukemia virus (A-MuLV)-transformed cell lines from prelymphomatous E mu-N-myc mice (A-MuLV/E mu-N-myc cell lines). Although these A-MuLV/E mu-N-myc lines express very high levels of the N-myc transgene, they continue to transcribe the endogenous c-myc gene. These findings demonstrate that high-level N-myc gene expression alone does not necessarily lead to down-regulation of endogenous myc gene expression and suggest that events associated with transformation by N-myc may be critical to this process.

Animals↗