Effects of low- and moderate-intensity training on metabolic responses to exercise in thoroughbreds.

This experiment was undertaken to determine whether there were differences in cardiorespiratory, haematological and muscular responses in horses trained at either low or moderate intensities. Ten Thoroughbred horses previously rested in paddocks for 4 months were trained 5 days/week for 9 weeks. Horses were allocated randomly into fast or slow groups and exercised the same distance each day. Training distances were 1600 m in Weeks 0 and 1 up to 4000 m in Week 9. The fast group were trained at an intensity inducing a post training blood lactate of 4-8 mmol/l. This intensity was determined for each horse each week. The slow group trained at half the speed of the fast group (blood lactate < 2 mmol/l). Horses performed a standardised exercise test prior to (Week 0) and on Weeks 1, 2, 3, 4, 7 and 9 of training. HR, VO2, VCO2 and blood lactate concentration were recorded during the last 15 s of each step. Blood samples were collected at the end of each test for determination of red cell and plasma volume. Muscle biopsies were collected from the middle gluteal muscle before training and after 4 and 9 weeks training. Training intensity had few effects on the majority of variables measured and results for both groups are combined unless otherwise stated. Bodyweight was unaffected by training. Economy of locomotion decreased from 12.0 +/- 0.4 ml/kg bwt/m prior to training to 13.8 +/- 0.6 ml/kg bwt/m at the end of training in the fast group. Run time to fatigue was not affected by training intensity. VO2max increased from 120.3 +/- 4.8 to 144.7 +/- 3.5 ml/kg bwt/min with a significant correlation between run time and VO2max. Peak HR was 221.4 +/- 2.5 beats/min prior to training and 226.5 +/- 1.7 beats/min after the first 4 weeks of training. V200 and VLa4 increased in response to training. Similarly, VLa4 increased from 7.0 +/- 0.5 to 9.2 +/- 0.2 m/s with VLa4 correlated to VO2max. Plasma volume decreased from 29.1 +/- 1.7 to 25.8 +/- 0.9 l during the last 3 weeks of training. Blood volume, red cell volume and/or red cell volume/kg were unaffected by intensity or duration of training. The activity of CS in muscle increased in the first 5 weeks of training whereas HAD activity was not affected by intensity or duration of training.

Structure of a new crystal form of a DNA dodecamer containing T.(O6Me)G base pairs.

The structure of the synthetic dodecamer (d[CGTGAATTC(O6Me)GCG])2 has been determined to a resolution of 2.25 A and refined to a final R factor of 16.7%. The volume of the unit cell is significantly smaller by 16% than the original Drew and Dickerson parent dodecamer [Drew, H. R., Wing, R. M., Takano, T., Broka, C., Tanaka, S., Itakura, K., & Dickerson, R. E. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 7318-7322]. The double helix is in a different position in the unit cell, rotated by -85.9 degrees, and translated by 9.9 A around the helical axis with respect to the parent structure. The intermolecular arrangement of helices, characterized by double hydrogen bonded guanine-guanine minor groove interactions, remains conserved. The molecular geometry exhibits several significant changes that are related to the changed position of the helix and the presence of two mismatched base pairs with O6-methylguanine. Both mispairs are found in a symmetrical T(anti).(O6Me)G(anti) conformation, and the methyl groups are in proximal orientation. The hydration pattern of the structure is different and can be related to changes in the minor groove geometry. An incorrect model that was isomorphous to the parent dodecamer could be refined to a low R factor. Characteristics of the refinement and of the geometry that are indicative of incorrect structures have been analyzed.

Effect of treadmill incline and speed on metabolic rate during exercise in thoroughbred horses.

We examined the effect of treadmill speed and incline on O2 uptake (VO2), CO2 production, heart rate (HR), plasma lactate concentration, economy of locomotion, stride frequency, and stride length. A further aim was to examine the relationships between HR and VO2 and lactate and VO2 and whether these relationships vary with alterations in treadmill incline. The experiment was a latin square design, using five horses and five treadmill inclines (0, 2.5, 5.0, 7.5, and 10.0%). Fit Thoroughbred horses exercised for 4 min at 3 m/s at 0% slope, after which the treadmill was set to the allocated incline. Speeds tested ranged from 1 to 13 m/s. The relationships of VO2 and CO2 production with speed were curvilinear at 0 and 2.5% and linear at 5, 7.5, and 10% inclines. There was a linear relationship of HR and speed with a significant effect of incline. The plasma lactate concentration increased exponentially with speed, and there was a significant effect of incline. Stride length increased linearly and stride frequency increased in a curvilinear manner with speed but there was no effect of incline. There were linear relationships of HR with VO2 and HR with VO2 when expressed as percentage of maximum VO2 and maximum HR that were not affected by incline. The O2 cost of exercise on a 10% incline was approximately 2.5 times that for exercise on the flat. The strong relationship between the percentages of maximum HR and maximum VO2 indicates that over a wide range of exercise intensities the relative VO2 can be accurately predicted from measurements of HR.

Maximal accumulated oxygen deficit in thoroughbred horses.

Thoroughbred horses have a high aerobic capacity, approximately twice that of elite human athletes. Whereas the aerobic capacity of horses can be accurately measured, there have been no measurements of anaerobic capacity. The aim of this study was to determine whether maximal accumulated O2 deficit (MAOD) could be measured in horses and used as an estimate of anaerobic capacity, as in human athletes. Six fit Thoroughbred horses were used with the exercise protocol utilizing a treadmill set at a 10% incline. O2 uptake VO2 was measured via an open-flow system for seven submaximal speeds (3-9 m/s), and maximal VO2 (135 +/- 3 ml.kg-1.min-1) was determined. The horses performed three tests at 105 and 125% and six tests at 115% of maximal VO2. The MAOD test was performed with the treadmill accelerated rapidly from 1.5 m/s (mean acceleration time 8 s) to the calculated speed (11-14 m/s). VO2 was measured every 10 or 15 s, and the test ended when the horse no longer kept pace with the treadmill. The mean run times were 165, 98, and 57 s for intensities of 105, 115, and 125% maximal VO2. The mean MAOD values were 31 +/- 2, 30 +/- 1, and 32 +/- 2 (SE) ml O2 eq/kg for the three intensities (P > 0.05). The proportion of energy derived from aerobic and anaerobic sources was calculated from the difference between calculated O2 demand and the VO2 curve. There was no correlation between MAOD and maximal VO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Gait and respiration in standardbred horses when pacing and galloping.

The relationship between gait and the respiratory response to exercise was examined in five standardbred racehorses which exercised on a treadmill at a pace and a gallop. After an initial warm-up, respiratory rate and stride frequency were measured after one and two minutes of treadmill exercise at 80 per cent of maximal oxygen consumption (VO2max), after one minute at 100 per cent VO2max and after two minutes at 100 per cent VO2max (galloping horses only). Exercise at 100 per cent VO2max continued until the horses showed signs of fatigue. Arterial blood was collected during exercise and when they were fatigued for the measurement of oxygen and carbon dioxide tensions, haemoglobin saturation and pH. Venous blood temperature was also recorded. The mean (SE) time to signs of fatigue was significantly (P < 0.05) less in the pacing horses (7.2 [0.4] minutes) than in the galloping horses (8.0 [0.4] minutes). The mean (SE) resting PCO2 was 47.7 (1.9) torr. During the pacing and galloping exercises at 80 per cent and 100 per cent VO2max the PCO2 remained in the range of 41.1 to 66.8 torr, despite concurrent hyperthermia and acidosis. The PCO2 during exercise was not significantly dependent on gait or exercise intensity. The PO2 was significantly higher in pacing horses during exercise at 80 per cent VO2max (111 [7] vs 96 [6] torr). The mean (SE) arterial blood pH decreased from 7.428 (0.025) during pacing at 5 m sec-1 to 7.250 (0.042) when the horses were fatigued.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoimmunity induced by syngeneic splenocyte membranes carrying irreversibly adsorbed paramyxovirus.

Newcastle disease virus was adsorbed to a membrane fraction prepared from splenocytes, and the resulting preparation was injected into syngeneic C3H mice. Complement fixing and cytotoxic antibodies reactive with syngeneic tissue and intact cells developed, and some mice died with autoimmune disease characterized by wasting, severe kidney damage, and loss of lymphoid tissue as described previously for animals receiving the membrane fraction of a syngeneic lymphoma in which Newcastle disease virus had grown. Similar experiments were done with L929 mouse fibroblasts and allogeneic spleen membrane fractions. With syngeneic spleen tissue and L929 fibroblasts, serological evidence of autoimmunity appeared after several injections, but deaths from autoimmunity were considerably delayed unless Freund's complete adjuvant was given with the antigen. The results suggest that antigen modification occurs after adsorption of the paramyxovirus to normal tissue as well as lymphoma cell membranes.

Role of envelope proteins of paramyxoviruses in the modification of cell membrane antigens.

Adsorption of paramyxoviruses to separated membranes of tumor cells produces neoantigens that are immunogenic in syngeneic mice (xenogenization). Thus it became possible to study this process by using modified virus or virus fractions. Membranes with adsorbed viral derivatives produced an immune response which was measured by cytotoxic and complement fixing antibodies and the appearance of autoimmune disease. The effect of viral preparations with reduced F (fusion) protein activity was compared to treatment of membranes with equivalent amounts of active or inactive virus as measured by hemagglutination. Viral preparations without hemolytic activity showed diminished adsorption to membranes and the immune response was reduced. Triton X 100 and desoxycholate extracted from membranes immunogenic material with associated paramyxovirus antigens.

Autoimmunity induced by injection of virus-modified cell membrane antigens in syngeneic mice.

C3H/Bi mice developed autoantibodies after repeated inoculations of isolated membranes from primary tissue cultures of a syngeneic ascites lymphoma in which Newcastle disease virus had grown. This was in addition to the tumor transplantation resistance and cytotoxic antibodies previously demonstrated. The complement-fixing antibodies were completely removed from sera by adsorption with ascites tumor cells but only partially by normal mouse liver powder or C3H/Bi erythrocytes. With continued immunization, antibodies to deoxynucleoprotein and heterophile reagins also appeared. After several months, mice showing these serological reactions died with a wasting disease characterized by loss of lymphoid tissue and scarred, atrophied kidneys. No significant antibody response or autoimmune disease occurred in mice receiving membranes from uninfected syngeneic ascites lymphoma.

Antiviral immune cytolysis at an early stage of paramyxovirus infection.

Antiviral antibody and rabbit complement added as early as 5 min after infection, and with relatively low virus/cell multiplicity, lysed mouse ascites lymphoma cells infected with Sendai or Newcastle disease virus. Inactive Sendai virus at much higher input also sensitized ascites cells and mouse fibroblast monolayers to early antiviral immune cytolysis. At 4 C where adsorption but no penetration occurred, antibody removed virus from the cell membrane and little cytolysis was observed. The ascites cells were sensitive to antibody and complement at all times after the start of penetration and uncoating, indicating that viral envelope antigen is constantly present on the cell membrane. Significant cross-reactions by immune cytolysis between Newcastle disease virus- and Sendai virus-infected cells suggested possible participation of host antigens of the viral envelope. No comparable antiviral immune cytolysis was observed with influenza strains PR8 and WSN. Cell viability was estimated by dye exclusion and the ability to form acid from glucose as indicated by colorimetric pH of the medium. The relation of antiviral immune cytolysis to changes in the membrane resulting in cell fusion is considered.

Inhibition of protein synthesis in Krebs 2 ascites cells and cell-free systems by phenylalanine and its effect on leucine and lysine in the amino acid pool.

1. The inhibition of incorporation of (14)C-labelled amino acids into protein of whole cells by phenylalanine has been reproduced in a cell-free system. In both cases only the l-isomer was inhibitory. 2. The effect of phenylalanine on incorporation of [(14)C]leucine and [(14)C]lysine into protein was different in both whole cells and cell-free systems. 3. In whole cells inhibition of incorporation of leucine at 2.5mug./ml. was very rapid, but when the concentration was increased to 100mug./ml. the inhibition was not apparent for about 1hr. The kinetics of inhibition of lysine was the same at both these concentrations and was similar to that found with leucine at 100mug./ml. 4. Neither a lower specific radioactivity of the two amino acids in the pool nor a decrease in their pool size could be consistently related with inhibition of protein synthesis. 5. In the cell-free system l-phenylalanine inhibited the incorporation of leucine but not of lysine. 6. Charging of transfer RNA by leucine was markedly decreased in the presence of phenylalanine, whereas charging of transfer RNA by lysine was not.

Relation of catalase to substrate utilization by Mycoplasma pneumoniae.

No catalase activity was detected in four strains of glucose-grown Mycoplasma pneumoniae at any time during the replication of the organism. Exogenous catalase dramatically increased the O(2) uptake with glycerol, presumably by releasing inhibition caused by hydrogen peroxide. The effect of added catalase on the O(2) uptake of washed organisms with glucose as substrate was moderate and variable in degree. The production of hydrogen peroxide was demonstrated by the quantitative enzymatic assay for inorganic peroxide and by the fact that added pyruvate, which is non-enzymatically oxidized by H(2)O(2) to acetic acid and CO(2) could mimic the action of catalase.