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Biomedical subjects

S B Smith

Publications and source records attributed to S B Smith.

At least 91 records · Page 5Linked to original sources
PubMed1996

Overstretching B-DNA: the elastic response of individual double-stranded and single-stranded DNA molecules.

Single molecules of double-stranded DNA (dsDNA) were stretched with force-measuring laser tweezers. Under a longitudinal stress of approximately 65 piconewtons (pN), dsDNA molecules in aqueous buffer undergo a highly cooperative transition into a stable form with 5.8 angstroms rise per base pair, that is, 70% longer than B form dsDNA. When the stress was relaxed below 65 pN, the molecules rapidly and reversibly contracted to their normal contour lengths. This transition was affected by changes in the ionic strength of the medium and the water activity or by cross-linking of the two strands of dsDNA. Individual molecules of single-stranded DNA were also stretched giving a persistence length of 7.5 angstroms and a stretch modulus of 800 pN. The overstretched form may play a significant role in the energetics of DNA recombination.

Base Composition↗
PubMed1996

Effects of basic fibroblast growth factor on the retinal degeneration of the mi(vit)/mi(vit) (vitiligo) mouse: a morphologic and electrophysiologic study.

Basic fibroblast growth factor (bFGF) has been shown to rescue dying photoreceptor cells in the RCS rat, a model with a genetic defect of the RPE that impairs outer segment phagocytosis. The purpose of the present study was to determine whether intravitreal injection of bFGF would have a similar effect on photoreceptor cell death in the vitiligo (C57BL/6-mi(vit)/mi(vit)) mouse. This mutant mouse loses photoreceptor cells slowly over many months. Experimental evidence suggests that the primary cellular site of the defect is the RPE. In the present study, bFGF was prepared with and without heparin in PBS and injected intravitreally into vitiligo mice at ages 2, 4, 6, 8 and 13 weeks, surrounding the onset of photoreceptor cell death. Non-injected, PBS-injected and heparin/PBS injected mice served as controls. Scotopic ERG's were performed on one group of mice prior to killing. Mice were killed 4, 6 or 10 weeks following the injection and the eyes were processed for histology and analysed. The amplitude of the b-wave was significantly smaller in mice injected with bFGF/PBS than in PBS-injected and non-injected eyes regardless of the time of injection or duration following injection. Histological examination revealed that the number of rows of photoreceptor cells did not differ significantly between bFGF-injected, vehicle- or non-injected mice. Although slight improvement in the attachment of outer segments to RPE was observed in 4 week mutants injected with bFGF/heparin/PBS, a similar result was obtained in heparin/PBS injected mutants. In mice injected with bFGF without heparin, detachment was severe and gross disruption of neural retina was observed. There were significantly more macrophages and photoreceptor cells in the subretinal space in bFGF injected mice. It appears that at the dosages and times administered, bFGF does not improve the electrophysiological functioning of the retina nor retard the degeneration of the retina in the vitiligo mouse as it does in the RCS rat.

Animals↗
PubMed1996

A diet containing myristoleic plus palmitoleic acids elevates plasma cholesterol in young growing swine.

The objective of this study was to test the effect of a novel fatty acid mixture, enriched with myristoleic and palmitoleic acids, on plasma lipoprotein cholesterol concentrations. Weanling pigs were assigned to one of six groups and each group received a diet differing in fatty acid composition. Diets were fed for 35 days and contained 10 g added cornstarch/100 g (to provide baseline data) or 10 g added fatty acids/100 g. For those diets containing added fatty acids, extracted lipids contained 36% myristoleic plus palmitoleic acid combined (14:1/16:1 diet), 52% palmitic acid (16:0 diet), 51% stearic acid (18:0 diet), 47% oleic acid (18:1 diet), or 38% linoleic acid (18:2 diet). With the exception of the cornstarch diet, all diets contained approximately 30% myristic acid. There were no significant differences in weight gain across treatment groups (P = 0.22). All diets caused a significant increase in triglycerides and in total, low density lipoprotein, high density lipoprotein, and very low density lipoprotein cholesterol. The increase in total plasma cholesterol from pretreatment values was greatest in pigs fed the 14:1/16:1 and 18:1 diets. However, the increase in low density lipoprotein cholesterol from the pretreatment concentration was greatest in the 14:1/16:1-fed pigs. Increases in very low density lipoprotein cholesterol above pretreatment concentrations were lowest in 16:0-fed pigs and greatest in 18:1-fed pigs. Dietary fatty acids elicited changes in plasma fatty acids which generally were reflective of the diets, although the 18:0 diet did not alter plasma fatty acid concentrations and the 16:0 diet increased plasma 16:0 only at the end of the study. These results demonstrated that the combination of myristoleic plus palmitoleic acids increased plasma cholesterol in young pigs, suggesting that fatty acid chain length, rather than degree of unsaturation, is primarily responsible for the effects of fatty acids on circulating lipoprotein cholesterol concentrations.

Animals↗
PubMed1996

Interaction between clenbuterol and run training: effects on exercise performance and MLC isoform content.

The purpose of this study was to determine the separate and combined effects of clenbuterol (CB) administration and interval training on running performance and myosin light-chain (MLC) isoform expression in mouse skeletal muscle. Mice were randomly assigned to one of four treatment groups: 1) control (Con), 2) exercise (Ex), 3) drug (CB), or 4) exercise + drug (Ex + CB). CB and Ex + CB mice were given CB (1.6 mg/kg) orally 4 days/wk. Ex and Ex + CB mice were trained 4 days/wk on a motorized treadmill (3 sets of 3 min, 36-40 m/min, 10-17% grade, 30-s recovery). After 8 wk of treatment, exercise conditioning increased total work performed 58% in the Ex group during a run-to-exhaustion treadmill test, whereas CB decreased total work by 25% in the CB group; in combination with exercise training, CB treatment eliminated the Ex-induced increase in work. Polyacrylamide gel electrophoresis indicated that run training, CB treatment, or a combination did not (P > 0.01) promote changes in fast and slow MLC isoforms in the soleus, gastrocnemius, or tibialis anterior muscles. Although not different from each other after 8 wk, CB and Ex + CB treatments produced significantly greater values than Con and Ex for the following variables: muscle mass (17-46%), total protein (22-50%), and myofibrillar protein (19-53%). It was concluded that CB decreases exercise performance and that the combination of Ex and CB have antagonistic effects on running performance; the two treatments do not interact to diminish the anabolic effects of CB on skeletal muscle and do not alter MLC isoform profiles.

Animals↗
PubMed1996

Regulation of human renin mRNA expression and protein release in transgenic mice.

The renin-angiotensin system plays a major role in the regulation of blood pressure and electrolyte homeostasis in mammals. In this study, we subjected transgenic mice containing a human renin genomic construct to a variety of pharmacological and physiological manipulations to test whether expression of the human renin gene and release of active human renin in appropriately regulated in this model. These manipulations were designed to test major regulators of renin release, including angiotensin II, the macula densa, renal perfusion pressure, and beta-adrenergic receptors. We used human plasma renin concentration and human renal renin mRNA levels to document the response of the transgene to these stimuli. Human plasma renin concentration increased in response to both angiotensin-converting enzyme inhibition with captopril and isoproterenol and decreased after a high salt diet. A low salt or sodium-deficient diet did not stimulate renin release. Human renin mRNA levels in kidney increased after captopril but were unchanged in the other experimental groups. We also measured the levels of human renin mRNA in double transgenic mice containing the same human renin gene in addition to the human angiotensinogen gene. These mice are chronically hypertensive and have increased circulating levels of angiotensin II. Human renin mRNA levels in the kidney were paradoxically elevated compared with their single transgenic normotensive counterparts. These transgenic mice provide a model for examination of human renin regulation and may help elucidate the molecular mechanisms that regulate the gene in response to physiological cues.

Animals↗
PubMed1996

Rear foot inversion/eversion during gait relative to the subtalar joint neutral position.

Clinicians often fabricate foot orthotic devices at the subtalar joint neutral position (STNP) to mimic the position of the rear foot during midstance. However, rear foot motion during gait, relative to the resting standing foot position, not the STNP, is often reported in the literature. The motion of the rear foot relative to a valid estimate of the STNP is unknown. In this study, six experienced foot care specialists manually placed the rear part of the feet of nine subjects at the STNP seven or eight times to obtain a valid estimate of each subject's STNP. The worst-case mean and 95% confidence interval of the STNP estimate for any one subject was 0.0 degree +/- 0.7 degree. These nine subjects then walked on a motor-driven treadmill, set at 0.89 meters/sec, and three-dimensional estimates of each subject's rear foot inversion/eversion motion were obtained, then averaged over 6 to 26 strides. For most subjects, the rear foot was always everted during stance with mean and standard deviation maximal eversion (7.2 degrees +/- 1.2 degrees) occurring at 44% of the total gait cycle. The inversion/eversion orientation during swing was characterized by 1 degree to 2 degrees of eversion, with a small amount of inversion in early swing. These findings have implications for the fabrication of foot orthoses, since the rear foot is rarely near the STNP during stance.

Adult↗
PubMed1996

Depression of lipogenesis in swine adipose tissue by specific dietary fatty acids.

The objective of this study was to document the influence of specific dietary fatty acids on rates of lipid synthesis and sensitivity to insulin in porcine adipose tissue. Weanling pigs were assigned to one of six groups, and each group was fed diets containing 10 g/100 g of added cornstarch or 10 g/100 g of added fatty acid. The fatty acid-enriched diets contained either a combination of 14:1 plus 16:1 (14:1/16:1 diet), 16:0, 18:0, 18:1, or 18:2 (n-6). With the exception of the cornstarch diet, all diets contained approximately 35% 14:0. Subcutaneous adipose tissue samples were collected at slaughter from the area overlying the first cranial vertebra. Fresh samples were incubated for 2 h in 20 mM glucose and 0, 10, 100 or 1,000 microU/mL of porcine insulin. The smallest adipocytes were observed in adipose tissue from pigs fed the 16:0 or 18:2 diets. Glucose incorporation into lipids was greater (P < .05) in adipose tissue from cornstarch-fed pigs than in adipose tissue from the other treatment groups. Lipogenesis was 67, 53, 35, 32, and 20% lower (P < .05) in adipose tissue from 16:0-, 14:1/16:1-, 18:0-, 18:2-, and 18:1-fed pigs, respectively, than in adipose tissue from the cornstarch-fed pigs. Insulin increased lipogenesis by 19% (P < .05) in adipose tissue from the cornstarch-fed pigs and by 15 to 40% (P < .05) in adipose tissue from the 14:1/16:1-fed pigs. Insulin did not stimulate lipogenesis (P > .4) in adipose tissue from pigs fed the 16:0, 18:0, or 18:1 diets. The data suggest that fatty acid chain length and unsaturation are determinants in the effects of dietary fat and insulin on de novo lipogenesis.

Adipocytes↗
PubMed1996

Fatty acid composition of subcutaneous adipose tissue from male calves at different stages of growth.

The objective of this investigation was to compare fatty acid composition of calves from Bos taurus and Bos indicus cows across different stages of growth. Hereford (H) and Brahman (B) embryos were transferred to H or B cows (n = 58) to produce purebred Brahman (BB), purebred Hereford (HH), Hereford x Brahman (HB), and Brahman x Hereford (BH) offspring. Calves were castrated at 2 to 3 wk of age. Before weaning (210 d of age), calves were fed native grasses. After weaning, calves were fed a concentrate diet in dry-lot pens. Adipose tissue was obtained by biopsy at two times: at weaning during forage feeding and 3 mo after weaning when placed on feed. A third sample was collected from the fed steers at slaughter (approximately 430 d of age). Samples obtained by biopsy and after death were collected from the perianal region. Fatty acid composition for each sample was determined as the normalized percentage area means from the duplicate measures. Generally, BB calves grew slowest and BH steers grew fastest (P < .05). The BH steers exhibited 15 and 20% heavier (P < .05) carcasses per day of age than H-sired steers and BB steers, respectively. Adipose tissue samples from calves from Brahman sires or dams were less saturated (P < .05) than samples from calves from Hereford sires or dams. Differences in degree of unsaturation primarily were due to the percentages of monounsaturated fatty acids (MUFA). As calves became older, MUFA increased markedly, polyunsaturated fatty acids increased slightly (due to inverse, nearly proportional changes in 18:2 and 18:3), and saturated fatty acids decreased by 10 percentage units (P < .001). Thus, adipose tissue from Brahman and Hereford purebred and crossbred calves became markedly more unsaturated early postweaning; this change was less dramatic in the purebred Hereford calves.

Adipose Tissue↗
PubMed1996

Proficiency of foot care specialists to place the rearfoot at subtalar neutral.

The proficiency of clinicians to place a rearfoot at the subtalar neutral position is important for the treatment of patients with lower extremity dysfunctions, and especially for foot orthosis prescription, fabrication, and management. However, the ability of experienced foot care specialists to perform this task has not been statistically compared with an average capacity. In this study, eight experienced chiropodists and eight untrained physiotherapy students placed six rearfeet at the subtalar neutral position five times. Statistically, the foot care specialists were able to find the subtalar neutral position better than the students (mean 0.00 versus 0.99 degrees, SD 1.84 versus 2.97 degrees, range -5.27 degrees to 4.33 degrees versus -6.25 degrees to 9.27 degrees). This can be interpreted as stating that foot care specialists and untrained students place a rearfoot within +/- 1 degree of the subtalar neutral position 41.3% and 25.0% of the time, respectively. Corresponding values within +/- 2 degrees of the subtalar neutral position are 72.3 degrees and 47.6 degrees, respectively. Alternatively, it can be stated that experienced foot care specialists are within +/- 3.0 degrees of the subtalar neutral position 90% of the time. A corresponding value for the students is +/- 4.9 degrees. These results suggest that although experienced foot care specialists position a rearfoot at the subtalar neutral position better than untrained physiotherapy students, there is room for improvement.

Adult↗
PubMed1995

The insulin enhancer binding site 2 (IEB2; FAR) box of the insulin gene regulatory region binds at least three factors that can be distinguished by their DNA binding characteristics.

Located at approximately 230 bp upstream from the transcription start site, the insulin enhancer binding site 2 (IEB2) or FAR region of the insulin gene is one of several important sequences involved in regulating transcription of the gene. The present study was undertaken to characterize the transcription factors binding at the IEB2/FAR region of the rat insulin II gene and to compare these with factors known to bind to the equivalent sequence in the rat I and human insulin genes. An endocrine-enriched factor, EFD3, was identified, which bound to the sequence CAGGAG. A second factor (D4) was identified as the widely expressed factor USF (upstream stimulating factor), while a third factor (D5) remained largely uncharacterized. The binding affinities of these three factors differed in the three genes, suggesting that the role of the IEB2/FAR sequence may vary subtly between the rat insulin II, rat insulin I and human insulin genes.

Animals↗
PubMed1995

Lipid metabolism in pigs fed beef tallow or high-oleic acid sunflower oil.

The objectives of this study were to establish the effects of high-oleic sunflower oil (HOSO) and beef tallow on tissue fatty acids and stearoyl-CoA desaturase activities in swine; and to compare effects of HOSO and tallow on swine plasma triglycerides and lipoprotein-cholesterol fractions. Sixteen gilts were divided into two groups: eight fed a control diet containing 10 g/100 g beef tallow, and eight fed a diet containing 10 g/100 g HOSO. Plasma samples were obtained before feeding began and at 4 weeks and 8 weeks of dietary treatment. Samples were obtained from longissimus dorsi muscle, liver, adipose and duodenal mucosa for the measurement of fatty acid composition and stearoyl-CoA desaturase activity. The HOSO diet increased (P < 0.05) the concentrations (mumol/g wet weight of tissue) of 18:1 and 18:2 (n-6) in adipose tissue. In muscle from pigs fed the HOSO diet, concentrations of 14:0, 16:0, 16:1, 18:0, 18:1, and 18:2 (n-6) decreased (P < 0.05) relative to muscle from pigs fed the beef tallow diet; only 14:0 and 16:1 were reduced in liver by the HOSO diet. Stearoyl-CoA desaturase specific activity [(pmol 7 min-1 mg-1 microsomal protein)] was 40 percent lower, and activity expressed as pmol 7 min-1 g-1 tissue) was 20 percent lower, in adipose tissue of pigs fed HOSO (P < 0.05). No differences due to dietary treatment were observed for desaturase activity from muscle, liver or intestinal mucosa. Plasma triglycerides declined steadily in the tallow-fed pigs, possibly reflecting the lower percentages of liver 18:0 and 18:1 acids, relative to the HOSO-fed pigs. The animals responded similarly to the addition of fat (beef tallow or HOSO) to their diets with increased (P < 0.05) plasma total, LDL- and HDL-cholesterol by 4 weeks of treatment. Total cholesterol, LDL-, VLDL- or HDL-cholesterol were not different between pigs fed beef tallow or HOSO. Thus, differences in fatty acid composition of the diets were sufficient to alter tissue fatty acid composition and adipose tissue desaturase activity, but insufficient to alter plasma lipoprotein cholesterol.

Adipose Tissue↗
PubMed1995

Autoradiographic and biochemical assessment of rod outer segment renewal in the vitiligo (C57BL/6-mivit/mivit) mouse model of retinal degeneration.

Rod outer segment renewal was assessed in vitiligo (C57BL/6-mivit/mivit) mice using autoradiographic and biochemical methods. This process was examined because the number of phagosomes is reduced in this mouse. Rod outer segment renewal was detectable in the mivit/mivit retina. Within 24 hr of intraperitoneal injection of 3H leucine, there was a distinct band of radioactivity present at the junction of the ROS and RIS in mutant mice that was similar to controls. The displacement of the radioactive band progressed normally in the peripheral regions of the vitiligo retina, but did not in the posterior retina. Morphometric analysis of the posterior region of mutant retinas, indicated that the band of radioactivity became less distinct between 1 and 3 days post-injection. In vitiligo retinas it remained at 2.23 microns, whereas in controls, the band migrated 6.16 microns from the ROS base. When posterior regions of retinas were evaluated 8 days post-injection, there was no band discernible in the vitiligo retinas, but a very dense band at the ROS apex in controls. Assessment of incorporation of radioactivity into rhodopsin using SDS-PAGE indicated a progressive displacement of radio-labeled rhodopsin through the RER, but not as complete a progression through the outer segments. The elongation of the outer segments in the posterior regions of the mutant retina suggests impaired shedding. This, plus the lack of attachment in the posterior retina of photoreceptor cells to RPE in this mouse, seem to be likely causes for the decreased number of phagosomes.

Animals↗
PubMed1995

Ultrastructural features of retinal dystrophy in mutant vitiligo mice.

Ultrastructural features of the retinal pigment epithelium and photoreceptor cells were studied in vitiligo (C57BL/6 mivit/mivit) mice. Eyes from 12-day- to 56-week-old animals were analysed. Abnormal photoreceptors were seen in 12-day-old mice. By 3 weeks malformed outer segments were evident in the posterior and equatorial retina, but normal photoreceptors were present in the periphery. By 28 weeks, a marked gradient in cell loss was evident, with a progressive increase in cell viability along the posterior-peripheral axis. Viable intact photoreceptors were still present in the peripheral retina of 56-week-old mice. Melanosome content varied between adjacent pigment epithelium cells in both the posterior and peripheral retina. In the choroid, however, a steep posterior-peripheral gradient in melanosome content was evident with highest pigmentation in the periphery. In the optic nerve head region abnormal development of photoreceptors was correlated with proliferation of abnormal pigment epithelium cells. Accumulation of rod outer segment debris in the posterior and peripheral subretinal space preceded photoreceptor cell death. Short pigment epithelial microvilli without proper attachment to photoreceptors are suggestive of alterations in pigment-epithelium-photoreceptor interaction, which might affect photoreceptor differentiation and phagocytosis of rod outer segments by pigment epithelium cells.

Animals↗
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↗
PubMed1995

Effect of breed type and sex on the fatty acid composition of subcutaneous and intramuscular lipids of finishing steers and heifers.

Effects of breed type and sex on the fatty acid composition of subcutaneous neutral lipid and intramuscular neutral and phospholipids of longissimus lumborum muscle were investigated using 145 steers and 82 heifers that consisted of pure Japanese Black and Holstein and crossbreds among Japanese Black, Holstein, Japanese Brown, and Charolais. Steers and heifers were reared on a high plane of nutrition and were fed the same concentrate diet and rice straw. All animals were slaughtered serially and carcass composition was determined by dissection of the left side of the carcass. Breed type and sex differences of fatty acid percentages of carcass lipids were compared by adjusting the percentages to mean carcass fat percentages. Heifers had higher contents of 18:1 and total monounsaturated fatty acids in subcutaneous and intramuscular neutral lipids than steers (P < .05). The fatty acid composition of intramuscular phospholipids differed between sexes for 16:0, 20:1, and 20:5, but the differences were small. Breed differences were significant (P < .05) in steers for 16:0, 16:1, 18:1, and total saturated and monounsaturated fatty acids in both subcutaneous and intramuscular neutral lipids, and iso-16:0, 16:0, and total saturated fatty acids in phospholipids, respectively. However, in heifers, fewer fatty acids differed (P < .05) among breed types in the neutral lipids. It is suggested that the Japanese Black has a genetic predisposition for producing carcass lipids containing higher concentrations of monounsaturated fatty acids than Holstein, Japanese Brown, or Charolais.

Animals↗
PubMed1995

Lipogenic activity of intramuscular and subcutaneous adipose tissues from steers produced by different generations of angus sires.

Simmental and Hereford cows (n = 74) were inseminated with semen from purebred Angus bulls from the 1960s or with semen from purebred Angus bulls from the 1980s. The F1 calves provided the foundation for two investigations, one addressing growth and carcass characteristics, and another measuring the impact of sire generation on lipid metabolism and adiposity. Calves sired by the 1980s-type bulls had greater (P < .05) birth, weaning, and final live weights and carcass weights. They also had larger (P < .05) hip heights and hip widths at weaning and larger (P < .05) hip heights and lower (P < .05) body condition scores at slaughter. There were no differences (P > .05) in any measure of fatness between groups (adjusted fat thickness, kidney, pelvic, and heart fat, or marbling scores), but yield grade was higher numerically (P < .1) for the 1980s steers. The second aspect of this research addressed the influence of different generations of Angus sires on specific carcass traits and adipose tissue metabolism. A subset of six steers for each generation type (from Simmental cows) were selected and samples were collected at slaughter for measurements in vitro. For both generation types, intramuscular (i.m.) adipocytes had lesser (P < .05) cell volumes than subcutaneous (s.c.) adipose tissue. Correspondingly. i.m. adipose tissue exhibited lower (P < .05) rates of 14C-labeled acetate incorporation into lipids as measured immediately after slaughter. Intramuscular and s.c. adipocytes from 1980s-type steers were smaller (P < .05) than those from the 1960s-types steers, with correspondingly more cells per gram of tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗