Cardiovascular and metabolic adaptations in horses competing in cross-country events. (1/2369)

The cardiovascular and metabolic response to two cross-country events (CC*: preliminary level and CC*** advanced level) were analysed in 8 male eventing horses (4 Anglo-Hunter and 4 Anglo-Arabian). This study focused on the establishment of the main metabolic pathways involved in the muscle energy resynthesis during the competitions. Heart rate (HR) was recorded throughout the CC events. Jugular venous blood samples were withdrawn before the warm-up period, immediately after the competitions and at 5 and 10 min in the recuperation period. The following haematological parameters were studied: red blood cells (RBC), packed cell volume (PCV), haemoglobin concentration (Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), white blood cells (WBC), and number and percentages of lymphocytes (LYM) and granulocytes and monocytes (GRAN). One fraction of blood was centrifuged and, in plasma, lactate (LA), total plasma protein (TPP) and the rate of LA disappearance were determined. The competitions induced significant increases in RBC, Hb, PCV, MCV and TPP. Plasma LA response exceeded the anaerobic threshold of 4 mmol/l, reaching a maximum level of 13.3 mmol/l. HR ranged from 140 to more than 200 bpm, peaking at 230 bpm, revealing a limitation in the oxygen supply to the working muscles. It was concluded that muscle energy resynthesis during a CC event is provided both through oxidative processes and glycolysis with LA formation. Therefore, both stamina and power exercises are required for eventing horses.  (+info)

Morphometric study of the equine navicular bone: variations with breeds and types of horse and influence of exercise. (2/2369)

Navicular bones from the 4 limbs of 95 horses, classified in 9 categories, were studied. The anatomical bases were established for the morphometry of the navicular bone and its variations according to the category of horse, after corrections were made for front or rear limb, sex, weight, size and age. In ponies, navicular bone measurements were smallest for light ponies and regularly increased with body size, but in horses, navicular bone dimensions were smallest for the athletic halfbred, intermediate for draft horse, thoroughbreds and sedentary halfbreds and largest for heavy halfbreds. The athletic halfbred thus showed reduced bone dimensions when compared with other horse types. Navicular bones from 61 horses were studied histomorphometrically. Light horses and ponies possessed larger amounts of cancellous bone and less cortical bone. Draft horses and heavy ponies showed marked thickening of cortical bone with minimum intracortical porosity, and a decrease in marrow spaces associated with more trabecular bone. Two distinct zones were observed for the flexor surface cortex: an external zone composed mainly of poorly remodelled lamellar bone, disposed in a distoproximal oblique direction, and an internal zone composed mainly of secondary bone, with a lateromedial direction for haversian canals. Flexor cortex external zone tended to be smaller for heavy ponies than for the light ponies. It was the opposite for horses, with the largest amount of external zone registered for draft horses. In athletic horses, we observed an increase in the amount of cortical bone at the expense of cancellous bone which could be the result of reduced resorption and increased formation at the corticoendosteal junction. Cancellous bone was reduced for the athletic horses but the number of trabeculae and their specific surfaces were larger. Increased bone formation and reduced resorption could also account for these differences.  (+info)

The physiological strain index applied to heat-stressed rats. (3/2369)

A physiological strain index (PSI) based on heart rate (HR) and rectal temperature (Tre) was recently suggested to evaluate exercise-heat stress in humans. The purpose of this study was to adjust PSI for rats and to evaluate this index at different levels of heat acclimation and training. The corrections of HR and Tre to modify the index for rats are as follows: PSI = 5 (Tre t - Tre 0). (41.5 - Tre 0)-1 + 5 (HRt - HR0). (550 - HR0)-1, where HRt and Tre t are simultaneous measurements taken at any time during the exposure and HR0 and Tre 0 are the initial measurements. The adjusted PSI was applied to five groups (n = 11-14 per group) of acclimated rats (control and 2, 5, 10, and 30 days) exposed for 70 min to a hot climate [40 degrees C, 20% relative humidity (RH)]. A separate database representing two groups of acclimated or trained rats was also used and involved 20 min of low-intensity exercise (O2 consumption approximately 50 ml. min-1. kg-1) at three different climates: normothermic (24 degrees C, 40% RH), hot-wet (35 degrees C, 70% RH), and hot-dry (40 degrees C, 20% RH). In normothermia, rats also performed moderate exercise (O2 consumption approximately 60 ml. min-1. kg-1). The adjusted PSI differentiated among acclimation levels and significantly discriminated among all exposures during low-intensity exercise (P < 0.05). Furthermore, this index was able to assess the individual roles played by heat acclimation and exercise training.  (+info)

Exercise-induced alterations in skeletal muscle myosin heavy chain phenotype: dose-response relationship. (4/2369)

This study investigated the effects of exercise training duration on the myosin heavy chain (MHC) isoform distribution in rat locomotor muscles. Female Sprague-Dawley rats (120 days old) were assigned to either a sedentary control group or to one of three endurance exercise training groups. Trained animals ran on a treadmill at approximately 75% maximal O2 uptake for 10 wk (4-5 days/wk) at one of three different exercise durations (30, 60, or 90 min/day). Training resulted in increases (P < 0.05) in citrate synthase activity in the soleus and extensor digitorum longus in both the 60 and 90 min/day duration groups and in the plantaris (Pla) in all three exercise groups. All durations of training resulted in a reduction (P < 0.05) in the percentage of MHCIIb and an increase (P < 0.05) in the percentage of MHCIIa in the Pla. The magnitude of change in the percentage of MHCIIb in the Pla increased as a function of the training duration. In the extensor digitorum longus, 90 min of daily exercise promoted a decrease (P < 0.05) in percentage of MHCIIb and increases (P < 0.05) in the percentages of MHCI, MHCIIa, and MHCIId/x. Finally, training durations >/=60 min resulted in an increase (P < 0.05) in the percentage of MHCI and a concomitant decrease (P < 0.05) in the percentage of MHCIIa in the soleus. These results demonstrate that increasing the training duration elevates the magnitude of the fast-to-slow shift in MHC phenotype in rat hindlimb muscles.  (+info)

Hypotension induced by exercise is associated with enhanced release of adenyl purines from aged rat artery. (5/2369)

To determine whether the antihypertensive effects of exercise are associated with release of ATP and its metabolites from arteries, we assayed blood pressure and the release of adenine nucleotides and nucleosides from the caudal arteries of exercised and sedentary aged hypercholesterolemic rats. Exercise on a treadmill for 12 wk significantly decreased the rise in systolic and diastolic blood pressure by 7.5 and 15.9%, respectively, with advanced age. The concentrations of oleic, linoleic, and linolenic acids in the caudal artery decreased significantly with exercise, demonstrating an association between exercise and the unsaturation index of caudal arterial fatty acids. The amounts of total adenyl purines released by the arterial segments from exercised rats, both spontaneously and in response to norepinephrine, were significantly greater by 80.0 and 60.7%, respectively, than those released by tissues from sedentary rats. These results suggest that exercise alters the membrane fatty acid composition in aged rats as well as the release of ATP from vascular endothelial cells and that these factors are associated with the regression of the rise in blood pressure normally observed with advanced age.  (+info)

Acute exercise can improve cardioprotection without increasing heat shock protein content. (6/2369)

The aim of this study was to determine the effects of acute bouts of exercise on myocardial recovery after ischemia and heat shock protein expression. Adult female Sprague-Dawley rats were divided into five groups: 1) 1-day run (1DR; n = 6) and 2) 3-day run (3DR; n = 7), in which rats ran for 100 min at a speed of 20 m/min up a 6 degrees grade for 1 or 3 consecutive days; 3) 1-day cold run (1CR), in which rats ran the same as 1DR but with wet fur at 8 degrees C, which prevented an elevation of core temperature (n = 8); 4) heat shock sedentary (HS), in which rats had their core temperatures raised to 42 degrees C one time for 15 min (n = 5); and 5) sedentary control (n=15). Cardiac function was analyzed 24 h after the last treatment using an isolated, working heart model. Nonpaced hearts were initially perfused under normoxic conditions, then underwent 17 min of global, normothermic (37 degrees C) ischemia, and, finally, were allowed to recover for 30 min under normoxic conditions. The concentration of the 72-kDa heat shock protein (HSP 72) was measured in each left ventricle. Compared with that in the sedentary group, recovery of cardiac output x systolic pressure (CO x SP) was enhanced (P < 0.05) in all treatment groups when the postischemic value was covaried with the preischemic value. No differences in CO x SP were found (P > 0.05) between the following groups: 1DR vs. 3DR, 1DR vs. HS, and 1DR vs. 1CR. Heat shock protein concentration was significantly greater (P < 0.05) than that in the sedentary controls in HS, 1DR, and 3DR groups, but not for 1CR. The concentration of HSP 72 was not significantly correlated with postischemic CO x SP (R2 = 0.197, P > 0.05). We conclude that acute bouts of exercise can produce cardioprotective effects without an elevation of HSP 72.  (+info)

Diastolic compliance is reduced in obese rabbits. (7/2369)

Obesity often leads to symptoms of cardiopulmonary congestion associated with normal systolic but abnormal diastolic function. This study analyzed alterations in passive diastolic compliance in obesity using the rabbit model. New Zealand White rabbits were fed a normal (n=8) or 10% added fat diet (n=8). After 12 weeks, rabbits fed the high fat diet developed obesity (5.34+/-0.11 versus 3.68+/-0. 04 kg, P+info)

Histology and tissue chemistry of tidemark separation in hamsters. (8/2369)

Adult articular cartilage is divided by the tidemark into a deep calcified layer and a more superficial uncalcified layer. Histologic examination of articular cartilage from the knee joint of golden Syrian hamsters 123 days of age or older revealed defects at the tidemark in the tibia. Defects ranged from small separations of the calcified and uncalcified layers along the tidemark to progressively larger defects apparently formed by dissolution. These larger defects appeared as cavities in the noncalcified cartilage, had smooth rather than rough edges, frequently contained coalesced debris, and often resulted in a bulge in the articular surface. Occasionally, these large defects broke through the articular surface. Defects were not observed in tibial cartilage of younger (<90 days old) hamsters or in femoral cartilage from hamsters of any age. Exercise neither protected against nor increased the severity of the defects. Collagen cross-linking by pyridinoline was examined as a function of age and increased from 1,090 to 3,062 micromoles of pyridinoline/mole of hydroxyproline over the period of 1-9 months of age but was not correlated with defect formation. With increasing age, these focal tidemark defects could lead to osteoarthrosis-like cartilage lesions.  (+info)