Blood chemistry changes in the rat induced by high doses of nitronyl free radical spin traps.

For greatest efficacy, it is desirable to use spin trapping agents in the highest concentrations possible. Fifty-four male Sprague-Dawley rats were used to explore the relative toxicity of four representative nitronyl spin traps at doses chosen on the basis of earlier lethality studies. Most studies were confined to the 3- to 6-h period following drug injection, because the behavioral signs of toxicity are most evident early after injection and because spin trapping studies would typically be performed within this time frame. Doses of spin trap were dissolved in a corn oil/buffer vehicle and injected intraperitoneally (i.p.). Toxic signs were recorded periodically, and at the time of euthanasia or spontaneous death a blood sample was collected by cardiac puncture for clinical chemistry analysis and a necropsy was performed. Both gross pathology and histopathological examination of the major organs were essentially negative in all cases, with no obvious evidence of cellular damage being observed. Neither DMPO (232 mg/100 g b.wt.) nor PBN (100 mg/100 g b.wt.) were lethal in the present study, while both M4PO (20 and 40 mg/ 100 g b.wt.) and PyOBN (100 and 200 mg/100 g b.wt.) were lethal. Abnormal clinical chemistry findings were generally confined to those animals that died spontaneously or were euthanized early for humane reasons. In most cases, death was associated with marked seizure activity and impaired respiration, and deaths occurred within a few min to a few hours. The mechanism of toxicity was unclear due to the lack of histopathological evidence and the wide range of abnormal serum analytes in those rats killed by either M4PO or PyOBN. In conclusion, during the first 6 h after IP administration there is little indication of tissue damage by the nitrone spin traps until the dose is increased to a lethal level, at which point an acute, rapidly occurring, wide-spread disruption of tissue integrity seems to occur.

Mediation of 8-hydroxy-guanine formation in DNA by thiazin dyes plus light.

We have discovered that methylene blue plus light mediates the formation of 8-OHdG in DNA. Methylene blue is one of several thiazin dyes and we report here that the other thiazin dyes tested, in combination with white light, are effective in mediating 8-OHdG formation in DNA. The effectiveness of light plus the thiazin dyes in forming 8-OHdG in DNA were as follows: methylene blue greater than azure B greater than azure A greater than toluidine blue greater than thionin. Two other compounds tested; riboflavin and fuschin acid, in combination with light, caused formation of very little, if any, 8-OHdG in DNA. Thiazin dye mediated formation of 8-OHdG in DNA was not inhibited by the spin trap alpha-phenyl-t-butyl nitrone, which supports our previous observations that oxygen free radical scavengers did not inhibit methylene blue plus light mediated 8-OHdG formation in DNA. Ascorbate addition to methylene blue plus DNA, in the absence of light, was ineffective in mediating 8-OHdG formation in DNA.

Ontogenic development of gastrointestinal motility: IV. Duodenal contractions in preterm infants.

Duodenal motility was studied by intraluminal manometry in 27 healthy infants of 26 to 42 weeks, gestational age. The frequency of contractions, the number of contractions per burst, and the intraluminal peak pressure during contractions all increased during a narrow postconceptual period, 29 to 32 weeks, regardless of length of gestation before birth. Antenatal beta-methasone administration to the mothers of 11 additional infants of 26 to 32 weeks gestational age was associated with increased duodenal contraction rate, number of contractions per burst, and intraluminal peak pressure compared with infants of similar gestational age whose mothers did not receive beta-methasone. The maturational effect of beta-methasone on duodenal motility was most pronounced in infants whose gestational age at birth was 26 to 29 weeks. Seven infants of 31 weeks' or longer gestational duration who had a CNS abnormality or insult had fasting duodenal contraction rates that were less than one half of the rate for normal infants of similar gestational age. These observations suggest that neonatal duodenal motility undergoes marked maturational changes between 29 and 32 weeks after conception and that these changes may be inducible before 29 weeks by corticosteroid administration. An intact CNS appears to be required for full expression of the maturational changes.

Relationship of human milk pH during course of lactation to concentrations of citrate and fatty acids.

Human milk pH was measured in 309 samples obtained from 52 women who had delivered at term and lactated for as long as 10 months thereafter. The mean pH decreased from 7.45 for colostrum to a nadir of 7.04 during the second week of lactation. Thereafter, the pH of milk remained between 7.0 and 7.1 until 3 months postpartum and then increased gradually to 7.4 by 10 months. The change in hydrogen ion concentration in milk was associated with corresponding changes throughout lactation in the concentration of citrate but not with the concentration of lactose. Lactose concentration increased gradually for 3 weeks; the concentration of saturated medium-chain fatty acids increased more rapidly. One interpretation of these findings is that the hydrogen ions and citrate generated by mammary secretory cell metabolism are used after the second week of lactation for de novo synthesis of fatty acids more rapidly than they are synthesized. Milk samples from ruminants were found to have concentrations of hydrogen ions and citrate that are greater than and pH that is less than the respective measurements in human milk. The significance for the recipient infant of the predictable changes in human milk pH during lactation and of the higher pH of human milk throughout lactation relative to bovine milk is unknown. However, drug excretion into milk, milk enzyme activity, milk leukocyte function, and neonatal gastrointestinal function are affected by ambient pH and may be influenced by the pH of milk.

Baseline characteristics of subjects in the Lipoprotein and Coronary Atherosclerosis Study (LCAS) with fluvastatin.

A total of 429 subjects (79 women and 350 men), aged 35-75 years, have been enrolled in a randomized clinical trial of fluvastatin therapy for hypercholesterolemia. The progression and regression of atherosclerotic lesions will be assessed by quantitative angiography and positron emission tomography (PET) after 2.5 years of treatment. Patients were included in the trial if they had angiographically documented lesions that occluded 30-75% of the diameter of a major coronary vessel. Of the 429 subjects, 99 were also studied by PET at rest and during static exercise of sustained handgrip combined with administration of dipyridamole. All subjects were instructed in an American Heart Association/National Cholesterol Education Program (AHA/NCEP) Step I or Step II diet. Of the total, 107 subjects (25%) had low density lipoprotein cholesterol (LDL-C) > or = 160 mg/dL and were given cholestyramine, 8 g/day. All subjects were randomized to placebo or fluvastatin, the newest 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor to be introduced into the U.S. market. Fluvastatin is entirely synthetic and is similar in efficacy to the other available HMG-CoA reductase inhibitors. Its pharmaceutical profile (i.e., low systemic exposure) makes fluvastatin a good candidate for use in combination lipid-lowering therapy. The majority of subjects were recruited through a community campaign and the remainder through cardiac catheterization laboratories and the medical records of hospitals in the Texas Medical Center. Approximately 8,500 prospects from the community campaign were screened and 272 were randomized, a conversion rate of approximately 3%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fluvastatin on coronary atherosclerosis in patients with mild to moderate cholesterol elevations (Lipoprotein and Coronary Atherosclerosis Study [LCAS]).

Despite the potential for reduced morbidity and mortality, aggressive intervention against mild to moderate hypercholesterolemia in patients with coronary heart disease (CHD) remains controversial and infrequently practiced. Eligible patients in the 2.5-year Lipoprotein and Coronary Atherosclerosis Study were men and women aged 35 to 75 years with angiographic CHD and mean low-density lipoprotein (LDL) cholesterol of 115 to 190 mg/dl despite diet. Patients (n = 429; 19% women) were randomized to fluvastatin 20 mg twice daily or placebo. One fourth of patients were also assigned open-label adjunctive cholestyramine up to 12 g/day because prerandomization LDL cholesterol remained > or = 160 mg/dl. The primary end point, assessed by quantitative coronary angiography, was within-patient per-lesion change in minimum lumen diameter (MLD) of qualifying lesions. Across 2.5 years, mean LDL cholesterol was reduced by 23.9% in all fluvastatin patients (+/- cholestyramine) (146 to 111 mg/dl) and by 22.5% in the fluvastatin only subgroup (137 to 106 mg/dl). Primary end point analysis (340 patients) showed significantly less lesion progression in all fluvastatin versus all placebo patients, deltaMLD -0.028 versus -0.100 mm (p <0.01), and for fluvastatin alone versus placebo alone, deltaMLD -0.024 versus -0.094 mm (p <0.02). A consistent angiographic benefit with treatment was seen whether baseline LDL cholesterol was above or below 160 or 130 mg/dl. Beneficial trends with treatment were also consistently seen in clinical event rates but were not statistically significant. Thus, lipid lowering by fluvastatin in patients with mildly to moderately elevated LDL cholesterol significantly slowed CHD progression.

Laboratory profile of sickle cell disease: a cross-sectional analysis. The Cooperative Study of Sickle Cell Disease.

We have collected steady-state laboratory data for over 2600 patients, age 2 years and over, with sickle cell anemia (HbSS), HbSC disease, and HbS-beta(+)-thalassemia. The packed cell volume (PCV) is lower in males than in females until 17 or 18 years of age in HbSS and ages 13 to 15 in HbSC, but then becomes consistently higher in males. After age 40, the PCV falls in HbSS. The steady-state leukocyte count in HbSS is higher than that in normals, blunting the utility of this measurement in the assessment of infection. In HbSC and HbS-beta(+)-thalassemia, the leukocyte counts are more often within the range of normal. Platelet counts in HbSS are often found to be above normal and show a downward trend with age. There is a progressive rise in creatinine with age. In HbSS, this rise begins at age 14 and may be accounted for by the increased muscle mass that occurs with puberty. The further deterioration of renal function in patients over 20 may be a result of the known adverse effects of sickle cell disease upon the kidney. Our data provide a basis to compare perturbations caused by intercurrent complications and new therapies, as well as to contrast with similar information from other populations of patients with sickle cell disease.

Rapid detection of giardia antigen in stool with the use of enzyme immunoassays.

Enzyme-linked immunosorbent assays (ELISAs) using sera from rabbits and goats immunized with Giardia trophozoites were compared for detection of Giardia antigen in 300 stool specimens, 80 of which had positive results for Giardia by microscopic examination. The diagnostic accuracy of the two assays was similar, with sensitivities of 92% and 87% and specificities of 87% and 91% with the use of rabbit and goat antisera, respectively. Both ELISAs detected Giardia antigen in stool samples from asymptomatic as well as symptomatic excretors and from treated patients after organisms were no longer visualized by microscopic examination. The specificity of the assays was confirmed by consistently negative results on stool specimens from 10 neonates and 27 patients with enteric parasitic infections other than Giardia. Negative results also occurred when stool specimens containing 21 bacterial enteropathogens were tested. Potential confounding variables including multiple freezing and thawing episodes, prolonged storage, and stool filtration did not affect test results from clinical specimens. Antidiarrheal compounds did not interfere with assay results. Preservation of specimens in formalin did interfere with the assay, even if formalinized stool specimens were dialyzed before testing. For diagnosis of giardiasis, the ELISA is a sensitive and specific test that is not influenced by many environmental factors or by other enteropathogens. This test provides a practical and reliable method for evaluating large numbers of specimens in a variety of clinical and epidemiologic settings.

Reactive oxygen in skeletal muscle. I. Intracellular oxidant kinetics and fatigue in vitro.

We hypothesized that muscle fiber bundles produce reactive oxygen intermediates and that reactive oxidant species contribute to muscular fatigue in vitro. Fiber bundles from rat diaphragm were mounted in chambers containing Krebs-Ringer solution. In studies of intracellular oxidant kinetics, bundles were loaded with 2',7'-dichlorofluorescin, a fluorochrome that emits at 520 nm when oxidized; emissions were quantified using a fluorescence microscope. Emissions from unstimulated muscles increased over time (P < 0.001). Accumulation of fluorescence was slowed by addition of catalase (P < 0.001) or superoxide dismutase (P < 0.001) and was accelerated by repetitive muscular contraction (P < 0.05). To determine effects of reactive oxygen intermediates on fatigue, curarized bundles were stimulated to contract isometrically; force was measured. Catalase, superoxide dismutase, and dimethyl sulfoxide were screened for effects on low- and high-frequency fatigue. Antioxidants inhibited low-frequency fatigue [after 5 min of repetitive contractions, force at 30 Hz was 20% greater than control (P < 0.015)] and increased the variability of fatigue at 30 Hz (P < 0.03). Antioxidants did not alter high-frequency (200-Hz) fatigue. We conclude that 1) diaphragm fiber bundles produce reactive oxygen intermediates, including O2-. and H2O2; 2) muscular contraction increases intracellular oxidant levels; and 3) reactive oxygen intermediates promote low-frequency fatigue in this preparation.

Renal pedicle torsion after simultaneous kidney-pancreas transplantation.

BACKGROUND: Simultaneous kidney-pancreas transplantation has become a recognized therapy for type I diabetes mellitus patients with diabetic nephropathy, neuropathy, and retinopathy. In the vast majority of these procedures, both grafts are placed intraperitoneally, which reduces posttransplant morbidity. Recently, in some of our recipients, we noted renal dysfunction related to complications of the renal pedicle. Our objectives in this study were to identify the cause of this renal dysfunction and to prevent its occurrence in future recipients. STUDY DESIGN: We undertook a retrospective chart review of simultaneous kidney-pancreas recipients who experienced renal dysfunction related to renal pedicle complications. RESULTS: We found four recipients with renal dysfunction related to renal pedicle torsion, diagnosed by serial ultrasound scans and kidney graft biopsies. Early diagnosis allowed salvage of three kidney grafts, but one was lost after late diagnosis. CONCLUSIONS: A high level of suspicion is needed to diagnose renal pedicle torsion. If simultaneous kidney-pancreas recipients have recurrent renal dysfunction, and rejection has been excluded, serial ultrasound scans with color flow Doppler examinations are needed. Once the diagnosis is made, a nephropexy to the anterior abdominal wall is indicated to prevent further torsion and save the kidney graft. We recommend prophylactic nephropexy of left renal grafts if the renal pedicle is > or = 5 cm long and if there is a 2 cm or more discrepancy between the length of the artery and the vein.

Using light sensitometry to evaluate mammography film performance.

The performance of commercially available light sensitometers was compared with two other methods of x-ray sensitometry to determine whether commercially available sensitometers are viable for evaluating clinical performance of mammography film. X-ray sensitometry was performed using mammography screens that were modified to accommodate a graded optical step tablet (screen sensitometry). Finally, a means for performing intensity-scale x-ray sensitometry was configured (inverse-square sensitometry). Clinical mammography x-ray exposure conditions were used and film processing quality was closely monitored during the study. Statistical results for chi-square probabilities on the resulting contrast curves yielded good agreement for most of the configurations investigated. Comparison of film gradient versus optical density curves showed good agreement for maximum contrast values and the corresponding optical density for maximum contrast for three of the four screen-film combinations used when comparing light sensitometry to screen sensitometry. A similar comparison of light sensitometers to inverse-square sensitometry showed good agreement for maximum contrast, but less agreement for the corresponding optical density of maximum contrast. Based on these results, the authors concluded that commercially available sensitometers could be used to estimate clinical film performance for the screen-film systems tested. In particular they can be used to determine the range of optical densities that provide optimal film contrast.

Enalapril in the prevention of restenosis following intracoronary intervention in a swine model.

BACKGROUND: Restenosis following percutaneous transluminal coronary angioplasty continues to be a major limitation of the procedure. To test whether an angiotensin-converting enzyme inhibitor may reduce restenosis, this study utilized an atherosclerotic, stented, Hanford miniature swine model of restenosis. METHODS: Each animal first was started on an atherogenic diet and had balloon abrasion of the left anterior descending and right coronary arteries. Four months later, balloon-mounted coil stents were placed into the abraded coronary arteries of each animal. Twenty-four animals then were randomly assigned to one of two groups: enalapril, and control. The enalapril group received 50 mg orally twice daily starting 1 week before intracoronary stenting. RESULTS: Follow-up 2 months later revealed angiographic stenosis in the control group of 30% +/- 13%/25% +/- 10% (left anterior descending/right coronary artery) versus 37% +/- 9%/20% +/- 11% in the enalapril group (P = not significant). The change in minimal lumen diameter from immediately after stenting to follow-up was not significantly different between control and enalapril groups. Area stenosis and maximal intimal thickness obtained by morphometric analysis were also compared, and the mean percentage area stenosis for the control group was 39 +/- 12%/31% +/- 16% and for enalapril 36% +/- 14%/35% +/- 19%. The maximal intimal thickness in the control group was 573 microns +/- 204 microns/605 microns +/- 266 microns and in the enalapril group 530 microns +/- 220 microns/424 microns +/- 237 microns. There was no statistical difference. CONCLUSIONS: Enalapril fails to reduce restenosis in this animal model.

Amiprilose in the prevention of restenosis after coronary intervention in a swine model.

BACKGROUND: Amiprilose hydrochloride is a synthetic carbohydrate with anti-inflammatory and antiproliferative properties. This study tested the potential benefit of amiprilose in preventing coronary artery restenosis in a swine model. METHODS: The swine restenosis model was prepared using Hanford miniature swine made atherosclerotic with coronary abrasion, high-fat and high-cholesterol feeding, and intracoronary stenting. Eighteen animals were randomized to receive amiprilose, 100 mg/kg body weight orally twice per day (n = 9), or no amiprilose (n = 9) beginning 5 days before stenting and continuing through 4 weeks until sacrifice. Presacrifice quantitative coronary angiography and postsacrifice histologic examination revealed the degree of intimal proliferation. RESULTS: Coronary angiography revealed no difference in percentage-diameter stenosis between the amiprilose and control groups (left anterior descending artery [LAD], 46% +/- 10% vs 44% +/- 17%; circumflex artery [CFX], 43% +/- 21% vs 42% +/- 15%; right coronary artery [RCA], 37% +/- 11% vs 34% +/- 9%; P = not significant [NS]), respectively, or in change in lumen diameter from poststenting to presacrifice (LAD, -1.0 +/- 0.4 mm vs -1.1 +/- 0.7 mm; CFX, -1.2 +/- 0.8 mm vs -1.0 +/- 0.7 mm; RCA, -1.1 +/- 0.4 mm vs -1.0 +/- 0.4 mm; P = NS). Morphometric histologic analysis likewise showed no difference in percentage-area stenosis (LAD, 55% +/- 14% vs 55% +/- 15%; CFX, 53% +/- 15% vs 54% +/- 12%; RCA, 39% +/- 17% vs 39% +/- 20%; P = NS) or in maximal intimal thickness. CONCLUSION: Amiprilose hydrochloride did not prevent coronary intimal proliferation in this swine model of restenosis.

Iron deficiency in female athletes: its prevalence and impact on performance.

The prevalence of iron deficiency and its impact on performance have not been adequately investigated in non-endurance athletes. This study evaluated these factors in 100 female intercollegiate athletes in various sports, and in 66 non-athletes. All subjects had determinations of hemoglobin, ferritin, and transferrin saturation. Athletes reported on diet, menses, and symptoms. Athletes and coaches described mood and performance. Iron-deficient athletes were treated with iron; others received placebo. The same data were collected at season's end. Initially 31/100 (31%) athletes had iron deficiency (ferritin less than 12 ng.ml-1; transferrin saturation less than 16%, or both) compared to 30/66 (45.5%) controls (not statistically significant). Compared to normal athletes, iron-deficient athletes did not have more symptoms of iron deficiency or differences in mood state, but they considered their performance to be worse (P less than 0.05). Their total iron intakes were similar, as were menstrual blood losses. At re-evaluation, 7/45 (15.6%) initially normal athletes were iron-deficient; 14/22 (63.6%) initially iron-deficient athletes were normal. Athletes receiving an iron supplement and their coaches did not report a greater improvement in performance or mood than athletes receiving a placebo. Female college athletes frequently had iron deficiency that could be successfully treated during the season, while some untreated normal athletes became iron-deficient. Iron deficiency and its treatment had no significant impact on symptoms or mood, but affected subjective assessment of performance.

Morphology and body composition predict ovipositional history of female smokybrown cockroaches (Dictyoptera: Blattidae) in the laboratory.

We tested the hypothesis that presence and color of shed follicles in ovarioles of smokybrown cockroaches, Periplaneta fuliginosa (Serville), were correlated with the number of oothecae deposited in the laboratory. There were no shed follicles in females not having oviposited, whereas all females that had deposited 1-4 oothecae had shed follicles or resorption bodies, and females that had deposited > or = 5 oothecae had only shed follicle cells in the base of ovarioles. Other important correlates of female age (days after adult eclosion) were abdominal fat-free, thoracic fat and fat-free masses, and leg fat mass. Oocyte length could be substituted for oocyte fat and fat-free mass because these variables were correlated with oocyte length. Crop mass and delay in dissection after oothecal deposition were not correlated to female age or number of oothecae. Mass of body fractions (fat and fat-free) increased as females deposited additional oothecae. A generalized linear model predicted that as thoracic fat mass increased the number of oocytes already deposited by a female increased. In addition, the model predicted that red follicles would be found in females having deposited 1-3 oothecae and yellow follicles were predicted to be found in females having deposited > 2 oothecae.

Chronobiologic evaluation of blood pressure in school children.

Blood pressure (BP) and heart rate (HR) data were collected over 24 h with an ambulatory BP monitor to (a) determine the existence of 12-, 24-, and combined 12- and 24-h BP patterns in children as previously noted for adults; (b) provide MESOR (an acronym for midline estimating statistics of rhythm), amplitude, and acrophase data for subgroups of students by race and gender; and (c) determine the influence of HR (as an estimate of activity) on BP and BP patterns for 100 normal, healthy students 9-12 years of age. We found no statistically significant differences between various racial groups or between gender for MESOR, amplitude, acrophase, or degree of sinusoidality of circadian rhythmicity (R2 values) for BP; clinically interesting differences were observed, including lower MESOR BPs in Hispanic males when compared with their female counterparts and slightly higher MESOR BPs in blacks of both genders when compared with whites. In addition, we demonstrated subgroups of students who exhibited specific 24-h and combined 12- and 24-h patterns. Also, 67% of subjects showed stable or nonrhythmic BP patterns, perhaps related to BP sampling intervals. Differences in HR, as a surrogate measure of activity, accounted for 56% of the variation in systolic BP but only 26% in diastolic BP over the 24 h.

Changes in circadian rhythm of blood pressure in on-call pediatric residents.

To provide an objective measure of the effects of on-call stress on the blood pressure (BP) of a group of pediatric residents, we used a SpaceLabs Ambulatory Blood Pressure Monitor (ABPM) to compare 37 pediatric residents' on- and off-call BPs. Residents wore the ABPM for 24 h (once on call and again off call) to assess systolic and diastolic BPs every 30 min during the day and hourly overnight. We found significantly higher MESOR (an acronym for midline estimating statistic of rhythm, which yields a mean value more representative of the true mean than an average of a series of measurements) BPs and BP loads (%BP readings > 135 mm Hg for systolic and/or 85 mm Hg diastolic) during the on-call period. Some residents became hypertensive on call, and the normal 24-h pattern of lower nighttime blood pressures was altered during this period. ABPM monitoring may prove useful in evaluating the effectiveness of interventions to reduce the stress of residency training.

Study of reproducibility of spin trapping results in the use of C-phenyl-N-tert-butyl nitrone (PBN) for trichloromethyl radical detection in CCl4 metabolism by rat liver microsomal dispersions. Biological spin trapping I.

The well-known metabolism of CCl4 to trichloromethyl radicals in rat liver microsomal dispersions has been reinvestigated with the goal to determine the repeatability and reproducibility of the EPR signal intensity of the EPR spectrum of the CCl3 adduct of PBN. It was found that at least eight repeat experiments were needed under identical conditions to obtain an average value with an error of +/- 10%. When the effect of changing the concentrations of CCl4, PBN or NADPH-generating system was investigated, the plots of EPR signal intensity vs. the variable selected showed initial smooth increases in signal strength with respect to an increase in concentrations of CCl4, PBN or NADPH-generating system. However, considerable scatter was found after the initial slope and only general trends could be recognized. It is concluded that with CCl4, no increase in EPR signal is found after 10 mM concentration. For PBN, the optimum concentration is about 30 mM. The signal strength seems to increase with increased amounts of NADPH generating system although with diminishing slope.

Control of Ia afferent input to triceps surae (soleus) locomotor nucleus precedes agonist muscle activation during gait.

Modulation of the triceps surae (soleus) H-reflex was investigated during treadmill walking to elucidate the temporal relationship between reflex facilitation and initiation of agonist muscle activation. Constant effective stimulation of the tibial nerve evoked the H-reflex. Contact foot switches monitored phases of the gait cycle. H-reflex changes were assessed at predetermined intervals across a window that anticipated the onset of soleus muscle electromyographic (EMG) activation. In five of six healthy subjects, multiphase statistical models revealed a 'breakpoint', reflecting a significant rise in H-reflex amplitude, beginning with stimuli delivered 144.1, 142.9, 148.8, 186.4 and 140.5 ms, respectively, prior to mean onset of EMG activity in the soleus muscle. In the sixth subject, no breakpoint was identified although the H-reflex amplitude gradually increased across the analysis window. These findings suggest that facilitation of the H-reflex is established well in advance of the descending corticomotoneuronal command to recruit spinal motoneurons in the motor act (i.e. prior to threshold spinal motoneuron depolarization). It is argued that a central programme controlling afferent input to the locomotor nuclei is part of the 'preparatory set' which precedes execution of the motor act.

Interday variation in vertical ground reaction force in clinically normal Greyhounds at the trot.

OBJECTIVE: To determine the effect of interday variation on vertical ground reaction force variables in dogs. ANIMALS: 52 clinically normal Greyhounds of either sex weighing between 22 and 35 kg. PROCEDURE: Dogs were led at a trot across a floor-mounted force platform to determine vertical ground reaction force variables (peak [PFz] and impulse [IFz]) from hind limbs. Data were collected from each dog on 3 consecutive days. Variance components were estimated, using maximal likelihood to evaluate contributions of interday variation within dogs and variation attributable to dogs and repetitions. An ANOVA was used to test significance of interday variation within dogs and day within dog interactions. RESULTS: PFz, IFz, or both differed significantly from day to day for 29 of 52 dogs. Only PFz differed significantly among days for 16 dogs, and only IFz differed among days for 5 dogs. The PFz and IFz differed significantly from day to day in 8 dogs. Using ANOVA, the difference for PFz and IFz among days within dogs was significant. CONCLUSIONS: Effect of day within dog variation (interaction) should be considered as a component in statistical models in which data from 1 day are evaluated against data from the same subject on another day. We propose a statistical model that incorporates an accommodation for interday variation. Investigators should determine the factors that affect their studies, including the extent of interday variation, and compensate for the variation attributable to each factor in the statistical models used to analyze their data.