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Biomedical subjects

D L Hawkins

Publications and source records attributed to D L Hawkins.

9 recordsLinked to original sources
PubMed2001

Race-start characteristics and risk of catastrophic musculoskeletal injury in Thoroughbred racehorses.

OBJECTIVE: To identify race-start characteristics associated with catastrophic musculoskeletal (MS) injury in Thoroughbred racehorses at 2 racetracks in Florida during 1995 through 1998. DESIGN: Matched case-control study. ANIMALS: 97 Thoroughbreds (case horses) that incurred a catastrophic MS injury during racing and 388 Thoroughbreds (control horses) randomly selected from noninjured participants and matched on the basis of racetrack and year. PROCEDURE: Incidence of MS injury was calculated for all race meets at 2 racetracks in Florida from 1995 through 1998. Race-start characteristics were compared among case and control horses, using conditional logistic regression. RESULTS: Overall incidence of MS injury was 1.2/1,000 race starts (97/79,416 starts). Incidence of injury was significantly higher for turf races (2.3/1,000 starts) than for dirt races (0.9/1,000 starts). Sex, number of days since last race, and racing surface were associated with risk of injury; geldings, > or = 33 days since the last race, and turf racing surface were associated with a higher risk of injury. CONCLUSIONS AND CLINICAL RELEVANCE: Incidence of injury among Thoroughbreds in Florida was associated with sex, number of days since last race, and racing surface. Days since last race may have been an indicator of previous health and lameness problems. Racing surface may have been a risk factor for MS injury because turf races tended to be more competitive than dirt races. Horses running in turf races were more likely to participate in races with a large field, handicap races, long races, and races with high purses.

Animals↗
PubMed2000

Estimating transition probabilities from aggregate samples plus partial transition data.

Longitudinal studies often collect only aggregate data, which allows only inefficient transition probability estimates. Barring enormous aggregate samples, improving the efficiency of transition probability estimates seems to be impossible without additional partial-transition data. This paper discusses several sampling plans that collect data of both types, as well as a methodology that combines them into efficient estimates of transition probabilities. The method handles both fixed and time-dependent categorical covariates and requires no assumptions (e.g., time homogeneity, Markov) about the population evolution.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Human interleukin 10 suppresses production of inflammatory mediators by LPS-stimulated equine peritoneal macrophages.

To investigate the ability of recombinant human interleukin 10 (rhuIL-10) to suppress the release of inflammatory mediators from lipopolysaccharide (LPS)-stimulated equine macrophages, rhuIL-10 was added to equine peritoneal macrophage monolayers at concentrations of 0, 0.1, 1, 10, or 100 ng/ml. Thirty minutes later, LPS (E. coli O55:B5) was added at final concentrations of 0, 1, 10, 100 ng/ml. Macrophages were incubated for 16 h at 37 degrees C, then supernates were harvested and assayed for tumor necrosis factor (TNF) activity (L929 cytotoxicity), interleukin-6 (IL-6) activity (B9 proliferation), prostaglandin E2 concentration (ELISA), and nitric oxide (Griess reaction for nitrite). Preincubation of LPS-stimulated peritoneal macrophages with rhuIL-10 caused significant (P<0.05) reduction in secretion of TNF, IL-6, and PGE2, in a dose-dependent manner. Of the inflammatory mediators, TNF was most sensitive to the effects of rhuIL-10. At concentrations of rhuIL-10> or =1 ng/ml, TNF activity in the supernate was inhibited significantly at all concentrations of LPS. At one or more LPS concentrations, there was significant inhibition of each mediator in the presence of 1 ng rhuIL-10/ml and, at 100 ng/ml, rhuIL-10 significantly inhibited production of each mediator at all LPS concentrations tested. When data were expressed as a percentage of control values and pooled across all LPS concentrations, both PGE2 and TNF values were significantly reduced at rhuIL-10 concentrations of > or =1 ng/ml, whereas IL-6 was inhibited significantly at concentrations of > or =10 ng rhuIL-10/ml. Tumor necrosis factor production was more completely suppressed (7.8% of control) by the highest concentration of rhuIL-10(100 ng/ml) than was PGE2 (27.2%) or IL-6 (43.8%). Nitrite was not detected in any supernate from peritoneal macrophage monolayers.

Animals↗
PubMed1997

Pregnancy-associated changes in material properties of the third metacarpal cortical bone in mares.

OBJECTIVE: To investigate the effect of late gestation, age, and parity on material properties of third metacarpal (MCIII) cortical bone in mares. ANIMALS: 8 healthy mares (treatment group) that died or were euthanatized within 24 hours after parturition because of foaling complications and 6 age-matched, healthy, nonpregnant mares (control group). PROCEDURES: After random assignment for mechanical testing and microradiography, the dorsal half of transverse mid-diaphyseal sections of each MCIII bone was divided into lateral, dorsal, and medial regions. Cylinders of bone from each of the 3 regions were tested in compression in a single cycle to failure. Contact microradiographic views were taken of 100-microns-thick sections prepared from methylmethacrylate-embedded transverse dorsal region specimens, which were further divided into periosteal, intracortical, and endosteal regions for assessment of bone mineral density and porosity. RESULTS: Postpartum mares had lower yield strain in the dorsal and medial regions and failure strain in the medial region. Increasing parity was associated with decreasing elastic modulus in the dorsal region and yield stress and failure stress in the lateral region. Age and parity were positively correlated (r = 0.865; P = 0.0001), but significant correlations were not found between treatment group and age or between treatment group and parity. Increasing age and parity were associated with increasing porosity in the periosteal region. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of the material properties evaluated for MCIII cortical bone in late pregnancy, any increased risk for fractures in mares in late gestation may be related to parity or age or both, and less likely to pregnancy pese.

Aging↗
PubMed1995

Effect of tumor necrosis factor antibody on synovial fluid cytokine activities in equine antebrachiocarpal joints injected with endotoxin.

Six horses received intra-articular injections of a mixture of 1 micrograms of endotoxin/5 mg of equine tumor necrosis factor (eqTNF) monoclonal antibody in 1 antebrachiocarpal joint and an equal volume (2 ml) of 1 micrograms of endotoxin/5 mg of control antibody in the opposite joint. Synovial fluid sample collection (1 ml) was accomplished by use of an indwelling, intra-articular catheter at postinjection hours (PIH) 0, 1, 1.5, 2, 5, and 8, and by arthrocentesis at PIH 24. Joint fluid samples were analyzed for nucleated cell count, protein concentration, and TNF, interleukin 6 (IL-6), IL-1, and IL-1-inhibitory activities. To monitor local inflammation, each carpus was graded semiquantitatively for swelling prior to each sample collection. Tumor necrosis factor, IL-1, or IL-1-inhibitory activity was not detected in any synovial fluid sample collected before endotoxin/antibody was administered. However, low IL-6 activity (< 100 U/ml) was found in 2 of 12 preinjection samples. In joints injected with endotoxin/control antibody mixture, maximal mean +/- SEM activities for TNF (1,019 +/- 310 U/ml), IL-1 (173 +/- 102 U/ml), and IL-6 (10.8 +/- 3.1 x 10(4) U/ml) were observed at PIH 2, 5, and 8, respectively. Tumor necrosis factor and IL-1 activities returned to baseline values by PIH 8 and 24, respectively; however, IL-6 activity remained high. Interleukin 1 inhibitory activity (27.4 +/- 2.25 IU/ml) was detected in all PIH-24 samples from control joints, but was not detected at any other time in control joints (limit of detection, 20 IU/ml). Tumor necrosis factor activity was not detected in any synovial fluid sample from joints treated with endotoxin/eqTNF antibody. In contrast, endotoxin IL-1 inhibitory activity (PIH 24) was higher in eqTNF antibody-treated joints (41.0 +/- 7.7 IU/ml) than in control joints, but the difference was not significant. Mean WBC count and protein concentration in control and treated joints were maximal at PIH 8. The curves for mean values of WBC count and total protein concentration were not significantly different in treated versus control joints. Swelling in each treated joint was either less than or the same as that in the opposite control joint at even, time in the initial 8 PIH. There was significant (P = 0.043) difference between treated and control joints at PIH 5 and 8. These results describe a profile of synovial fluid TNF, IL-1, IL-6 bioactivities, and IL-1-inhibitory activity during the initial 24 hours of synovitis induced by intra-articular administration of endotoxin in horses. Our eqTNF monoclonal antibody was effective in neutralizing TNF activity in synovial fluid when administered intra-articularly with endotoxin in horses. The induction of IL-1, IL-1 inhibitory activity IL-6, WBC, and total protein concentration responses are largely independent of TNF activity in synovial fluid of horses receiving endotoxin intra-articularly.

Animals↗
PubMed1993

Effects of intra-articularly administered endotoxin on clinical signs of disease and synovial fluid tumor necrosis factor, interleukin 6, and prostaglandin E2 values in horses.

In each of 4 horses, sterile synovitis was induced by intra-articular injection of 3 micrograms of Escherichia coli endotoxin (lipopolysaccharide, LPS) into one antebrachiocarpal joint; an equal volume (2 ml) of phosphate-buffered saline solution (PBSS) was injected into the opposite, control carpus. Blood and 1.5 ml of synovial fluid were obtained at postinjection hours (PIH) 0, 2, 4, 8, 12, 18, 42, 66, and 144. Synovial fluid sample collection was accomplished by use of an indwelling, intra-articular catheter through PIH 12, and by arthrocentesis subsequently. Joint fluid samples were analyzed for cell counts, protein concentration, cytologic variables, and tumor necrosis factor (TNF), interleukin 6 (IL-6), and prostaglandin E2 (PGE2) values. Tumor necrosis factor and IL-6 activities and WBC count were also measured in blood. To monitor local inflammation, skin temperature of each carpus was imaged, using a thermographic scanner prior to each sample collection time. Horses had minimal systemic effects. Mean (+/- SEM) rectal temperature increased significantly to 39.02 +/- 0.15 C only at PIH 18 after intra-articular injection of LPS. One horse had signs of mild depression from PIH 7 to 18, but its vital signs did not change appreciably. Each horse had mild signs of discomfort in the LPS-injected limb from PIH 1 to 3 until PIH 8 to 10. Mean peak surface temperature of the LPS-injected carpi was significantly higher than that of control carpi from PIH 8 to 144 (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1985

Estimating baseline values of the variable of intervention in a clinical trial.

Parametric empirical Bayes methodology is suggested for determining estimators of individual baseline values of the variable of intervention in a clinical trial, when the variable is measured twice--once for subject selection, and again, without selection, just before randomization. The resulting compromise estimator is seen to have more precision than the baseline estimator employing only the second value and less bias than the estimator that simply averages the two values. Construction of such an estimator is illustrated using data from the recruitment phase of the Lipid Research Clinics Coronary Primary Prevention Trial. Generalizations to other designs are also suggested. In all cases, however, an estimate of the intraindividual variance of the variable of intervention is required.

Analysis of Variance↗
PubMed1979

Plasma progesterone concentrations derived from the administration of exogenous progesterone to ovariectomized mares.

Six ovariectomized mares were divided into 3 groups to determine the effects of exogenous progesterone in oil and repositol progesterone on plasma progesterone concentrations. Progesterone in oil was administered in 7 daily injections in Exp. I. Progesterone concentrations were not maintained greater than 1.0 ng/ml for 24 h with 50 mg/day. However, they remained greater than 1.0 ng/ml during the last 4 days of 100 mg/day and greater than 1.5 ng/ml throughout the injection sequence of 200 mg/day. Repositol progesterone was administered on Days 1 and 7 in Exp. II. At 500 mg, progesterone concentrations peaked in 6 h but returned to near 1.0 ng/ml in 2 days. At 1000 mg and 2000 mg, plasma progesterone was maintained at approximately 2.0 and 4.0 ng/ml respectively for 7 days after injection on Day 1 and was 1.5 and 3.5 ng/ml respectively, 11 days after injection on Day 7. An indication of a cumulative effect on plasma progesterone was observed following repeated dosages of both progesterone in oil and repositol progesterone.

Animals↗