Structure and promoter activity of the mouse CDC25A gene

CDC25A is a member of a group of highly related, dual-specificity phosphatases that promote cell cycle phase transitions by regulating the activity of cyclin-dependent kinases. Here we report the cloning and genomic sequence of 21,067 nucleotides encompassing the mouse CDC25A gene. The coding sequence is expressed from 17,904 bp of genomic DNA comprising 15 exons. We also mapped the transcription initiation site to a consensus initiator element proximal to an SP1 site. Approximately 1 kb of sequence upstream of the transcription initiation site confers promoter activity and cell type specificity to a reporter gene construct. Surprisingly, transcription from this promoter was repressed by over-expression of catalytically active but not catalytically inactive CDC25A protein. We also show, using NIH 3T3 cells, that murine CDC25A mRNA levels fluctuate only modestly over the cell cycle. Our findings provide insights into the regulation of CDC25A expression and have facilitated construction of gene knock-out vectors.

Opinions and use of advance directives by physicians at a tertiary care hospital

The physician-patient relationship is an essential part of end-of-life planning, including discussions of advance directives (AD). Physicians likely to encounter AD issues with their patients were identified and queried as to their knowledge, opinion, and experience with ADs. Though most physicians felt ADs were helpful to both physicians and patients, considerably less were familiar with hospital policies and the different types of ADs. Formal education in the use and function of ADs also appears to be lacking, suggesting a need to improve the way in which ADs are addressed during medical training.

Evaluation of novel assays in clinical chemistry: quantification of plasma total homocysteine

BACKGROUND

There is a need for systematic evaluation of methods before their release to the market. We addressed this problem in novel homocysteine assays as part of an European Demonstration Project involving six centers in four countries.

METHODS

Two immunological methods for measurement of plasma total homocysteine (P-tHcy), the fluorescence polarization immunoassay (FPIA) and the enzyme immunoassay (EIA), were compared with two comparison methods, HPLC and gas chromatography-mass spectrometry (GC-MS). All laboratories performed the following procedures: (a) familiarization; (b) determination of linearity and precision by analyzing five plasma samples with interrelated concentrations for 20 days; (c) correlation using patients' samples; and (d) assessment of long-term performance.

RESULTS

Both immunological methods were linear for P-tHcy between 5 and 45 micromol/L. The intralaboratory imprecision (CV) was <5% for FPIA and <9% for EIA used with a sample processor. The bias was -2% to 3% for FPIA and 2-4% for EIA used with a sample processor.

CONCLUSIONS

The immunological methods provide results with little bias compared with HPLC and GC-MS. The imprecision of the assays must be considered in the context of their intended use(s).

Effects of stimulant medication treatment on mothers' and children's attributions for the behavior of children with attention deficit hyperactivity disorder

Participants were 55 children with attention deficit hyperactivity disorder (ADHD) who were receiving ongoing treatment with stimulant medications and their mothers, and 31 children with ADHD who were beginning stimulant medication and their mothers. Mothers and children offered attributions for child behaviors that occurred when the child was medicated and not medicated. Mothers rated child compliance and prosocial behavior as more global and stable when the child was medicated and rated noncompliance, ADHD symptoms, and oppositional behavior as more externally caused, less global and stable, but more controllable by the child when the child was medicated. Children rated both their compliance and noncompliance as more controllable in the medicated condition. On a forced-choice measure, both mothers and children selected ability, effort, and task attributions for compliance more in the not-medicated condition, and pill-taking attributions more in the medicated condition. This was reversed for noncompliance, which was attributed more to effort, task, or ability in the medicated condition and more to not taking a pill in the not-medicated condition. The potential risks and benefits for parent-child interactions and children's self-perceptions of these medication-related differences in attributions are discussed.

Acute pulmonary effects of ultrafine particles in rats and mice

Ambient fine particles consist of ultrafine particles (< 100 nm) and accumulation-mode particles (approximately 100 to 1,000 nm). Our hypothesis that ultrafine particles can have adverse effects in humans is based on results of our earlier studies with particles of both sizes and on the finding that urban ultrafine particles can reach mass concentrations of 40 to 50 micrograms/m3, equivalent to number concentrations of 3 to 4 x 10(5) particles/cm3. The objectives of the exploratory studies reported here were to (1) evaluate pulmonary effects induced in rats and mice by ultrafine particles of known high toxicity (although not occurring in the ambient atmosphere) in order to obtain information on principles of ultrafine particle toxicology; (2) characterize the generation and coagulation behavior of ultrafine particles that are relevant for urban air; (3) study the influence of animals' age and disease status; and (4) evaluate copollutants as modifying factors. We used ultrafine Teflon (polytetrafluoroethylene [PTFE]*) fumes (count median diameter [CMD] approximately 18 nm) generated by heating Teflon in a tube furnace to 486 degrees C to evaluate principles of ultrafine particle toxicity that might be helpful in understanding potential effects of ambient ultrafine particles. Teflon fumes at ultrafine particle concentrations of approximately 50 micrograms/m3 are extremely toxic to rats when inhaled for only 15 minutes. We found that neither the ultrafine Teflon particles alone when generated in argon nor the Teflon fume gas-phase constituents when generated in air were toxic after 25 minutes of exposure. Only the combination of both phases when generated in air caused high toxicity, suggesting the existence of either radicals on the particle surface or a carrier mechanism of the ultrafine particles for adsorbed gas-phase compounds. We also found rapid translocation of the ultrafine Teflon particles across the epithelium after their deposition, which appears to be an important difference from the behavior of larger particles. Furthermore, the pulmonary toxicity of the ultrafine Teflon fumes could be prevented by adapting the animals with short 5-minute exposures on 3 days prior to a 15-minute exposure. This shows the importance of preexposure history in susceptibility to acute effects of ultrafine particles. Aging of the fresh Teflon fumes for 3.5 minutes led to a predicted coagulation resulting in particles greater than 100 nm that no longer caused toxicity in exposed animals. This result is consistent with greater toxicity of ultrafine particles compared with accumulation-mode particles. When establishing dose-response relationships for intratracheally instilled titanium dioxide (TiO2) particles of the size of the urban ultrafine particles (20 nm) and of the urban accumulation-mode particles (250 nm), we observed significantly greater pulmonary inflammatory response to ultrafine TiO2 in rats and mice. The greater toxicity of the ultrafine TiO2 particles correlated well with their greater surface area per mass. Ultrafine particles of carbon, platinum, iron, iron oxide, vanadium, and vanadium oxide were generated by electric spark discharge and characterized to obtain particles of environmental relevance for study. The CMD of the ultrafine carbon particles was approximately 26 nm, and that of the metal particles was 15 to 20 nm, with geometric standard deviations (GSDs) of 1.4 to 1.7. For ultrafine carbon particles, approximately 100 micrograms/m3 is equivalent to 12 x 10(6) particles/cm3. Homogeneous coagulation of these ultrafine particles in an animal exposure chamber occurred rapidly at 1 x 10(7) particles/cm3, so that particles quickly grew to sizes greater than 100 nm. Thus, controlled aging of ultrafine carbon particles allowed the generation of accumulation-mode carbon particles (due to coagulation growth) for use in comparative toxicity studies. We also developed a technique to generate ultrafine particles consisting of the stable isotope 13C by using 13C-graphite electrodes made in our laboratory from amorphous 13C powder. These particles are particularly useful tools for determining deposition efficiencies of ultrafine carbon particles in the respiratory tracts of laboratory animals and the translocation of particles to extrapulmonary sites. For compromised animals, we used acute and chronic pulmonary emphysema; a low-dose endotoxin inhalation aimed at priming target cells in the lung was also developed. Other modifying factors were age and copollutant (ozone) exposure. Exposure concentrations of the generated ultrafine particles for acute rodent inhalation studies were selected on the basis of lung doses predicted to occur in people inhaling approximately 50 micrograms/m3 urban ultrafine particles. Concentrations that achieved the same predicted lung burden per unit alveolar surface were used in rodents. (ABSTRACT TRUNCATED)

A preliminary report of the use of botulinum toxin type A in infants with clubfoot: four case studies

This report describes the use of botulinum toxin type A (BTX-A) in four infants with very severe clubfoot deformity. The gastrocnemius and posterior tibial muscles were injected with BTX-A after the patients reached a treatment plateau in physical therapy. Significant improvement in foot dorsiflexion and foot flexibility was seen in two patients, and surgery was not required. Surgical intervention was necessary in the remaining two patients, both of whom were ultimately diagnosed with a demyelinating neuropathy. The use of botulinum toxin as an adjunct to conservative care in infants with clubfoot is discussed.

Is high titre ANA specific for connective tissue disease?

OBJECTIVE

A positive antinuclear antibody (ANA), while sensitive, is not specific for systemic lupus erythematosus or connective tissue diseases (CTD). The purpose of the present study was to review those sera with a high titre (> or = dilutions above screening) ANA and determine from a review of the charts if these higher titres offered a satisfactory specificity for CTD.

METHODS

All FANA testing in this region is carried out in one of two related laboratories. We reviewed the medical records of patients who had a positive ANA at a titre 4 dilutions above screening at this city-wide laboratory over a 6-month period to determine whether this titre ("high titre") may offer relative diagnostic certainty. Antibodies to extractable nuclear antigens (ENA) and native DNA were also obtained.

RESULTS

422 ANA results were positive at high titre. The medical record was available for review in 320 patients, of whom 238 (75%) were seen by a specialist physician, almost always including a rheumatologist. Our review determined that 35% had a diagnosis of connective tissue disease, 21% had a diagnosis of a possible/probable inflammatory disease, 16% had an alternative specific diagnosis provided, and in 29% no final disease specific diagnosis was recorded but CTD was not suggested to us or the specialist by the data available. One or more anti-ENA antibodies and/or anti-DNA were positive in 69 (22%) and 8% of the sera tested respectively.

CONCLUSION

While long term follow-up is still required, a significant proportion of patients with high titre ANA have no CTD at the time of testing. Setting a higher cutoff for reporting of ANA may not increase specificity sufficiently to make it a useful alternative or addition to reporting a positive or negative value at screening titre alone.

Northwest Herts diabetic management system

The Diabetic Management System was set up in Hemel Hempstead within the Dacorum district (population 119515 with 2176 registered patients with diabetes). The objective was to create a clinical management system for all patients with diabetes in a district using a computerised clinical base. To achieve this a database of agreed clinical information was collected from all general practitioners within the district. From the computerised data we can identify those patients who do not have data recorded and can recall them for review. Consultant advice can be given on patients with special or multiple risks identified from interrogation of the database. The outcome has been a higher percentage of patients with diabetes receiving clinical review and achieving optimal clinical targets within the reviews. We already have recorded data on 85% for retinal screening and 75% for comprehensive annual reviews. Conclusions drawn from the Dacorum Diabetic Management System are that effective diabetic care to a population can be provided by a combination of hospital and primary care. Primary care needs to be supported by adequate consultant advice with continued monitoring of the whole population to ensure standards are met. This system achieves this without increased hospital referrals.

Basic three-dimensional kinematics of the vertebral column of horses walking on a treadmill

OBJECTIVE

To determine kinematic movements of the vertebral column of horses during normal locomotion.

ANIMALS

5 Dutch Warmblood horses without apparent lameness or problems associated with the vertebral column.

PROCEDURE

Kinematics of 8 vertebrae (T6, T10, T13, T17, L1, L3, L5, and S3) and both tuber coxae were determined, using bone-fixated markers. Horses were recorded while walking on a treadmill at a constant speed of 1.6 m/s.

RESULTS

Flexion-extension was characterized by 2 periods of extension and flexion during 1 stride cycle, whereas lateral bending and axial rotation were characterized by 1 peak and 1 trough. The range of motion for flexion-extension was fairly constant for vertebrae caudal to T10 (approximately 7 degrees). For lateral bending, the cranial thoracic vertebrae and segments in the pelvic region had the maximal amount of motion, with values of up to 5.6 degrees. For vertebrae between T17 and L5, the amount of lateral bending decreased to <4 degrees The amount of axial rotation increased gradually from 4 degrees for T6 to 13 degrees for the tuber coxae.

CONCLUSIONS

This direct measurement method provides 3-dimensional kinematic data for flexion-extension, lateral bending, and axial rotation of the thoracolumbar portion of the vertebral column of horses walking on a treadmill. Regional differences were observed in the magnitude and pattern of the rotations. Understanding of the normal kinematics of the vertebral column in healthy horses is a prerequisite for a better understanding of abnormal function.

Induction of adaptation to inhaled lipopolysaccharide in young and old rats and mice

Lipopolysaccharide (LPS) is a component of the gram-negative bacterial cell wall that is known to activate inflammatory cells and enhance the production of inflammatory mediators in the lung. As it is a ubiquitous compound, inhalation exposure is highly likely in the human environment. Adaptation is a phenomenon by which a previous exposure results in improved survival or reduced injury as compared to a single exposure alone. We hypothesized that the basic proinflammatory effects of LPS in the lung could result in the development of adaptation in animals. Based on evidence of age- and species-related differences in lung injury, we used an acute lung injury model with inhaled LPS to compare the development of adaptation in young and old Fisher 344 rats and C57Bl/6J mice. Animals were exposed to low-dose (predicted lung deposition approximately 20 ng in rats and approximately 5 ng in mice) LPS aerosols for 10 min on 3 consecutive days; on day 4, a high dose (rats approximately 200 ng; mice approximately 25 ng) was delivered. Another group of animals received only the high LPS dose on day 4, whereas controls were unexposed. Twenty-four hours after the last exposure, cellular and inflammatory parameters in bronchoalveolar lavage (BAL) were determined. An adaptive response was found in both rats and mice. Adapted animals showed significantly fewer BAL neutrophils compared to nonadapted ones; there was also a significantly lower release of oxidants from phorbol methyl ester-stimulated BAL cells from adapted compared to nonadapted animals, which, in turn, showed a greater response than controls. Furthermore, studies in old animals (21 mo of age) showed that adaptation also occurs in this age group. The adaptive response is clear in old mice; in rats, there is greater variability in the response, but an adaptive trend is apparent. Therefore, we have demonstrated that inhaled low-dose LPS can induce adaptation to subsequent higher doses, much as has been shown for other toxicants that induce oxidative lung injury.

Silica binds serum proteins resulting in a shift of the dose-response for silica-induced chemokine expression in an alveolar type II cell line

There is a growing concern about whether the myriad of culture conditions, cell lines, and doses of nonfibrous and fibrous particles used in vitro are truly representative of the complex environment of the in vivo particle exposure situation. The use of serum as a supplement to the growth medium of cultured cells is a widely accepted practice. However, little is known about whether the various serum proteins may interact with the surfaces of particles, consequently altering their toxicity, inflammatory properties, or fibrogenicity, etc. observed in vivo. Using a murine alveolar type II cell line, MLE-15, we measured the early changes in various chemokine mRNA species following exposure of the cells to silica (cristobalite) in the presence or absence of serum. Total mRNA was isolated and assayed using an RNase protection assay after 6 h of particle exposure. We observed that the addition of serum to the culture media reduced the in vitro silica-induced chemokine response (i.e., shift in the dose-response curve) in MLE-15 cells. Further, using Western blot analysis and protein sequencing techniques, we have identified a specific serum component, apolipoprotein-A1 (apo-A1), as a protein in serum that binds selectively to silica, thus leading to the altered chemokine response. We also found that apo-A1 not only binds to silica but also binds to other nonfibrous and fibrous particles such as titanium dioxide and asbestos. These results demonstrate the importance of culture conditions for modifying the outcome of an experiment when performing in vitro particle exposure studies.

Advance directive use among patients undergoing selected high-risk surgical procedures

Since 1991, the Patient Self-Determination Act has required that all patients entering Medicare-reimbursed institutions be asked if they have an advance directive (AD) and be given information about advance directives if they do not have one. Patients undergoing elective high-risk surgery for diseases with a poor prognosis were identified as being most likely to benefit from an AD. The charts of patients being explored for possible pancreaticoduodenectomy or esophagectomy at a tertiary referral hospital in 1996 were retrospectively reviewed. Few patients had an AD, and there was little evidence that the presence of an AD affected patient care.

A decade of doctoral research in nutrition

OBJECTIVE

To describe North American dissertation research in human nutrition from 1986 through 1995.

DESIGN

A census collection.

SUBJECTS/SETTING

The unit of observation was the dissertation abstract submitted to Dissertation Abstracts International for the years 1986 through 1995. Only dissertations written in English with a human nutrition subject code (0570) that lead to a PhD, DrPH, EdD, or ScD at a North American university were included (N = 2,044). Abstracts were reviewed by 2 raters who extracted pertinent data on variables describing the dissertation research (e.g., topic of dissertation, type of sample).

ANALYSES

Analyses were descriptive.

RESULTS

The majority (n = 1,147) of doctoral dissertations were completed by female students. Male students were more likely to study in vitro samples than female students (11% vs 4%) and female students were more likely to study human subjects (64%). Male students tended to have male advisers, although overall male advisers appeared to predominate (34% men, 24% women, 42% unknown or missing). Topic areas for dissertation work reflected gender differences. Popular topics for dissertation research have changed over time; biochemical-, micronutrient-, and obesity-related research decreased and research in development of theoretical constructs and examination of dietary habits of selected groups increased.

CONCLUSIONS

From 1986 through 1995 there was an increase in the proportion of female doctoral students. Female and male students varied in the type of sample studied, gender of advisers, age group of human subjects, and topics of their dissertations. Universities emphasized different topic areas and methodologies. There appears to have been an increase in areas of applied research (e.g., dietary habits) and a decrease in basic science topic areas (e.g., micronutrients) over the 10-year period examined.

Antioxidant treatment attenuates cytokine and chemokine levels in murine macrophages following silica exposure

Alveolar macrophages play a key role in the development of silicosis by releasing a host of mediators, such as, cytokines and chemokines, which contribute to a complex network of interactions that result in the onset of lung injury, inflammation, and potentially fibrosis. Using a murine macrophage cell line, RAW 264.7, we exposed the cells to cristobalite-silica (35 micrograms/cm(2)) in the presence or absence of antioxidants and various modifiers of cellular antioxidant status. Treatment with dimethyl sulfoxide, extracellular glutathione, or N-acetyl-L-cysteine (NAC) decreased cristobalite-induced tumor necrosis factor (TNF)-alpha mRNA levels by 40%, 20%, and 42%, respectively. TNF-alpha protein levels were decreased by 90%, 32%, and 53%, respectively. Cristobalite-induced macrophage inflammatory protein (MIP)-2 mRNA levels were reduced by 52%, 38%, and 57%, with DMSO, GSH, and NAC treatment, respectively. Both MIP-1alpha and MIP-1beta mRNA levels were reduced at a magnitude similar to the reduction in TNF-alpha mRNA levels, whereas monocyte chemotactic protein (MCP)-1 mRNA levels were reduced at a magnitude similar to the reduction in MIP-2 mRNA levels following antioxidant treatment. These results suggests that the macrophage response to cristobalite exposure is mediated at least in part by oxidant stress.

Management of pain from heel lance with lidocaine-prilocaine (EMLA) cream: is it safe and efficacious in preterm infants?

Hospitalized preterm infants undergo multiple painful heel lances. A two-phase, randomized, controlled trial was undertaken to determine the safety and efficacy of lidocaine-prilocaine 5% cream (EMLA, Astra Pharmaceuticals, L.P, Westborough, MA) for relieving pain from heel lance. One hundred twenty infants were randomly assigned to receive 0.5 g of EMLA or placebo cream for 30 minutes (Phase 1) or 60 minutes (Phase 2) before a routine heel lance. Efficacy was assessed using the Premature Infant Pain Profile (PIPP). Safety was determined by methemoglobin concentration 8 hours after EMLA application and by clinical signs of methemoglobinemia. No significant differences existed on PIPP scores between EMLA and placebo groups in Phase 1 (p < .480) or Phase 2 (p < .831). No infant had any clinical signs of methemoglobinemia. The mean methemoglobin concentration was 1.19% (.47). Approximately 10% of infants had minor skin reactions, and approximately 20% of EMLA-treated infants had blanching at the application site. The authors conclude that EMLA is safe but not efficacious for relieving pain from heel lance in preterm infants.

Improved solution for solitary waves in arteries

Nonlinear waves are investigated numerically by a direct analysis of the field equations, thereby establishing the magnitude of the errors inherent in the commonly used reductive perturbation technique. The method is also applied beyond the long-wave approximation and a comparative assessment of the results obtained is presented.

The effect of shoeing on kinetics and kinematics during the stance phase

The increasing range of of horseshoes and hoofpads makes it important to be able to evaluate their influence on performance and stress in the locomotor apparatus. The aim of this study was to describe the changes in ground reaction forces and locomotion pattern during the stance phase due to the application of a standard iron shoe. Six Swedish Warmblood horses were evaluated kinetically and kinematically before and after they were shod with an 8 mm iron shoe. Data were used to calculate ground reaction forces in the vertical and craniocaudal directions, point of application of the force, hoof segment angle and hoof joint, pastern joint, fetlock, carpal and tarsal angles. Finally joint angular velocity and landing velocity of the hoof were calculated. During the initial phase of the stance or the concussion phase, the horses altered the conditions of the limb, as reflected by hoof-landing velocities. Concussion-dampening mechanisms of the distal limb subsequently were altered. In the nonshod condition, the coffin and fetlock joints rotated more rapidly in the forelimb and less rapidly in the hindlimb, while earlier proximal off-loading by the carpus and tarsus resulted in a decrease in initial horizontal loading at the hoof. It was concluded that horses accustomed to standard iron shoes demonstrate slight but significant differences in the movement and loading of the distal limb due to shoeing. Though the main differences were related to the concussion phase of the stance, even mid-stance loading and roll-over were altered. The study provides a basis for further investigation of the effect of various farriery techniques on the hoof and movement of the horse.

Nerve block and intra-articular anaesthesia of the forelimb in the sound horse

Nerve blocks and intra-articular anaesthesia are used extensively as routine methods in lameness evaluation. The method is based on the assumption that the technique itself does not change the movement pattern. The aim of this study was to carry out a quantitative kinematic study to confirm or reject the hypothesis that high palmar digital nerve block (HPDN) and intra-articular fetlock joint anaesthesia (IAF) influence significantly the movement pattern of the horse. Seven Standardbred horses trotting at 4.5 m/s were recorded at 240 Hz on a treadmill before and after anaesthesia by use of a ProReflex video system. Time variables, segment and joint angles were calculated. The high palmar digital nerve block (HPDN) resulted in a longer stance time and caused a greater fetlock joint angle range and greater maximal pastern joint angle. No systematic differences in time and angle variables were observed after intra-articular fetlock joint anaesthesia (IAF). In conclusion, HPDN but not IAF affects locomotor pattern in sound horses. Distal limb proprioception is important in normal movement, while fetlock intra-articular proprioception is apparently not. Interpretation of the effect of HPDN in lame individuals should incorporate more variables than maximal overextension of the fetlock joint.

Effects of flunixin on movement and performance of standardbred trotters on the track

An often discussed and controversial issue is the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on performance. The purpose of this study was to investigate the effect of the NSAID flunixin on the movement pattern and performance capacity of Standardbred trotters using a standardised track model. Five adult Standardbred horses in training trotted at 2 occasions with a 2 week interval on the same oval dirt track. Before each occasion the horses were either injected with flunixin meglumine (Finadyne) or normal saline solution i.m. 4 h before the performance test (double blind crossover study). The kinematics for 5 consecutive strides were filmed. There was no significant difference in maximal speed between the saline and flunixin treatment sessions. Significant changes in the movement pattern were observed as an effect of the flunixin treatment. The horses maintained the same stride duration while significantly decreasing stance time and increasing swing time in the forelimbs. The horses' range of limb angle decreased significantly. Heart rates were monitored and plasma lactate and flunixin concentrations were measured. No significant differences were found in heart rate and plasma lactate. The results indicate that flunixin had a significant effect on locomotor pattern while it did not effect metabolic response in these horses (considered to represent a normal race track population). The overall effect on performance in racing horses may therefore be related to the anti-inflammatory and analgesic properties of NSAIDs by masking pain and lameness.

The kinematics of loading and fatigue in the standardbred trotter

The Standardbred trotter must pull a considerable load when racing and, consequently, draught loading is a common method of training in the Standardbred and the effects of loading and fatigue due to loading on the locomotor pattern was the purpose of this investigation. Four mature healthy Standardbred horses trotted with and without a horizontal-pulling loading of 34 kg until the horses were no longer willing to keep pace with the treadmill despite encouragement. Heart rate was monitored every min using a bipolar electrocardiogram. The kinematics for 5 consecutive strides were filmed. Horses exercised on the treadmill for 7-10 mins. The mean heart rate was 206 beats/min at the end of the exercise. Due to draught loading, the horses reduced significantly the time of the stance phase in both the fore- and hindlimb. Three of the 4 horses reduced their stride lengths as the result of increased loading. The general movement pattern of the horses remained similar. More dramatic changes in the movement pattern were observed because of fatigue. The limbs of the horse were significantly more compressed as the result of greater joint excursion during the stance phase. Furthermore, the length of stride was significantly increased as the result of fatigue. The results show that both loading and fatigue change the locomotor pattern of the Standardbred trotter. Although the horizontal loading was considerable, the horse maintained similar joint movement with increases in stride frequency. During fatigue the horse seems to be unable to maintain stride frequency, probably due to a compromised power capacity of the muscles. The increase in joint excursion due to fatigue may have an important influence on certain types of injury to the locomotor system of the racehorse.