Thales Nicolau Prímola-Gomes

Thermoregulatory responses in exercising rats: methodological aspects and relevance to human physiology

Rats are used worldwide in experiments that aim to investigate the physiological responses induced by a physical exercise session. Changes in body temperature regulation, which may affect both the performance and the health of exercising rats, are evident among these physiological responses. Despite the universal use of rats in biomedical research involving exercise, investigators often overlook important methodological issues that hamper the accurate measurement of clear thermoregulatory responses. Moreover, much debate exists regarding whether the outcome of rat experiments can be extrapolated to human physiology, including thermal physiology. Herein, we described the impact of different exercise intensities, durations and protocols and environmental conditions on running-induced thermoregulatory changes. We focused on treadmill running because this type of exercise allows for precise control of the exercise intensity and the measurement of autonomic thermoeffectors associated with heat production and loss. Some methodological issues regarding rat experiments, such as the sites for body temperature measurements and the time of day at which experiments are performed, were also discussed. In addition, we analyzed the influence of a high body surface area-to-mass ratio and limited evaporative cooling on the exercise-induced thermoregulatory responses of running rats and then compared these responses in rats to those observed in humans. Collectively, the data presented in this review represent a reference source for investigators interested in studying exercise thermoregulation in rats. In addition, the present data indicate that the thermoregulatory responses of exercising rats can be extrapolated, with some important limitations, to human thermal physiology.

Brain Temperature in Spontaneously Hypertensive Rats during Physical Exercise in Temperate and Warm Environments

This study aimed to evaluate brain temperature (Tbrain) changes in spontaneously hypertensive rats (SHRs) subjected to two different physical exercise protocols in temperate or warm environments. We also investigated whether hypertension affects the kinetics of exercise-induced increases in Tbrain relative to the kinetics of abdominal temperature (Tabd) increases. Male 16-week-old normotensive Wistar rats (NWRs) and SHRs were implanted with an abdominal temperature sensor and a guide cannula in the frontal cortex to enable the insertion of a thermistor to measure Tbrain. Next, the animals were subjected to incremental-speed (initial speed of 10 m/min; speed was increased by 1 m/min every 3 min) or constant-speed (60% of the maximum speed) treadmill running until they were fatigued in a temperate (25°C) or warm (32°C) environment. Tbrain, Tabd and tail skin temperature were measured every min throughout the exercise trials. During incremental and constant exercise at 25°C and 32°C, the SHR group exhibited greater increases in Tbrain and Tabd relative to the NWR group. Irrespective of the environment, the heat loss threshold was attained at higher temperatures (either Tbrain or Tabd) in the SHRs. Moreover, the brain-abdominal temperature differential was lower at 32°C in the SHRs than in the NWRs during treadmill running. Overall, we conclude that SHRs exhibit enhanced brain hyperthermia during exercise and that hypertension influences the kinetics of the Tbrain relative to the Tabd increases, particularly during exercise in a warm environment.

Effect of exercise training on Ca2+ release units of left ventricular myocytes of spontaneously hypertensive rats

In cardiomyocytes, calcium (Ca2+) release units comprise clusters of intracellular Ca2+ release channels located on the sarcoplasmic reticulum, and hypertension is well established as a cause of defects in calcium release unit function. Our objective was to determine whether endurance exercise training could attenuate the deleterious effects of hypertension on calcium release unit components and Ca2+ sparks in left ventricular myocytes of spontaneously hypertensive rats. Male Wistar and spontaneously hypertensive rats (4 months of age) were divided into 4 groups: normotensive (NC) and hypertensive control (HC), and normotensive (NT) and hypertensive trained (HT) animals (7 rats per group). NC and HC rats were submitted to a low-intensity treadmill running protocol (5 days/week, 1 h/day, 0% grade, and 50-60% of maximal running speed) for 8 weeks. Gene expression of the ryanodine receptor type 2 (RyR2) and FK506 binding protein (FKBP12.6) increased (270%) and decreased (88%), respectively, in HC compared to NC rats. Endurance exercise training reversed these changes by reducing RyR2 (230%) and normalizing FKBP12.6 gene expression (112%). Hypertension also increased the frequency of Ca2+ sparks (HC=7.61±0.26 vs NC=4.79±0.19 per 100 µm/s) and decreased its amplitude (HC=0.260±0.08 vs NC=0.324±0.10 ΔF/F0), full width at half-maximum amplitude (HC=1.05±0.08 vs NC=1.26±0.01 µm), total duration (HC=11.51±0.12 vs NC=14.97±0.24 ms), time to peak (HC=4.84±0.06 vs NC=6.31±0.14 ms), and time constant of decay (HC=8.68±0.12 vs NC=10.21±0.22 ms). These changes were partially reversed in HT rats (frequency of Ca2+ sparks=6.26±0.19 µm/s, amplitude=0.282±0.10 ΔF/F0, full width at half-maximum amplitude=1.14±0.01 µm, total duration=13.34±0.17 ms, time to peak=5.43±0.08 ms, and time constant of decay=9.43±0.15 ms). Endurance exercise training attenuated the deleterious effects of hypertension on calcium release units of left ventricular myocytes.

Power spectrum analysis of cardiovascular variability during passive heating in conscious rats

The cardiovascular system plays a direct role in the maintenance of body temperature. Whether passive heating alters cardiovascular autonomic modulation in conscious rats is still unknown. This study investigated the effects of passive heating on systolic blood pressure variability (SBPV) and heart rate variability (HRV) in conscious rats and the involvement of the renin-angiotensin system in the passive heating effects on SBPV and HRV. Fourteen male Wistar rats were randomly assigned to the control group or the losartan treatment group. A catheter was implanted in the left carotid artery to record pulsatile arterial pressure (PAP), and a telemetry sensor was implanted in the abdominal cavity to measure body temperature (Tbody). After recovering from surgery, the animals were subjected to a passive heating protocol (35°C; 30min) in resting conditions, during which Tbody, tail skin temperature and PAP were measured. The mean arterial pressure, systolic and diastolic blood pressure, heart rate, double product (i.e., the product of systolic blood pressure by heart rate), SBPV and HRV were calculated from the PAP. SBPV and HRV were analyzed in terms of both time and frequency domains. Increases in the thermoregulatory and cardiovascular parameters were observed during passive heating in both groups, and those increases were reflected in the higher time and frequency domains of the SBPV. However, passive heating was not effective in altering HRV. Passive heating altered SBPV but not HRV in conscious rats when they were treated with losartan.

Mesenchymal stem cell therapy associated with endurance exercise training: Effects on the structural and functional remodeling of infarcted rat hearts.

We tested the effects of early mesenchymal stem cell (MSC) therapy associated with endurance exercise on the structural and functional cardiac remodeling of rats with myocardial infarctation (MI). Male Wistar rats (40 days old) were divided into 6 groups: control and exercise sham; control and exercise MI; and control and exercise MI MSC. MI was surgically induced and bone marrow-derived MSCs were immediately injected via caudal vein (concentration: 1 × 10(6 )cells). Twenty-four hours later ET groups exercised on a treadmill (5 days/week; 60 min/day; 60% of maximal running velocity) for 12 weeks. Structural and functional changes were determined by echocardiography. Contractility and intracellular global calcium ([Ca(2 +)]i) transient were measured in myocytes from the left ventricular (LV) non-infarcted area. Calcium regulatory proteins were measured by Western blot. MI increased (p < 0.05) heart, ventricular and LV weights and its ratios to body weight; LV internal dimension in diastole (LVID-D) and in systole (LVID-S) and LV free wall in diastole (LVFW-D), but reduced the thickness of interventricular septum in systole (IVS-S), ejection fraction (EF) and fractional shortening (FS). MI augmented (p < 0.05) the times to peak and to half relaxation of cell shortening as well as the amplitude of the [Ca(2 +)]i transient and the times to peak and to half decay. Early MSCs therapy restored LVFW-D, IVS-S and the amplitude and time to half decay of the [Ca(2 +)]i transient. Early endurance exercise intervention increased (p < 0.05) LVFW-S, IVS-S, EF and FS, and reduced the times to peak and to half relaxation of cell shortening, and the amplitude of the [Ca(2 +)]i transient. Exercise training also increased the expression of left ventricular SERCA2a and PLBser16. Nevertheless, the combination of these therapies did not cause additive effects. In conclusion, combining early MSCs therapy and endurance exercise does not potentiate the benefits of such treatments to structural and functional cardiac remodeling in infarcted rats.

Morfologia e contratilidade em cardiomiócitos de ratos com baixo desempenho para o exercício físico

BACKGROUNDnAerobic capacity is essential to physical performance, and low aerobic capacity is related to the triggering of various cardiovascular diseases.nnnOBJECTIVEnTo compare the morphology and contractility of isolated rat cardiomyocytes with low performance and standard performance for exercise.nnnMETHODSnWistar rats with 10 weeks of age underwent a protocol of treadmill running to fatigue, and were divided into two groups: Low Performance (LP) and Standard Performance (SP). Then, the animals were sacrificed, the heart was quickly removed and, by means of enzymatic dissociation, left ventricular cardiomyocytes were isolated. The cell and sarcomeres length and width of cardiomyocytes were measured using an edge detection system. The isolated cardiomyocytes were electrically stimulated at 1 and 3 Hz and cell contraction was measured by registering the change of their length.nnnRESULTSnThe cell length was shorter in the LP group (157.2 ± 1.3 µm; p < 0.05) compared to SP (161.4 ± 1.3 µm), and the same result was observed for the volume of cardiomyocytes (LP, 25.5 ± 0.4 vs. SP, 26.8 ± 0.4 pL; p < 0.05). The time to peak contraction (LP, 116 ± 1 vs. SP 111 ± 2 ms) and total relaxation (LP, 143 ± 3 vs. SP 232 ± 3 ms) were higher in the LP group.nnnCONCLUSIONnWe conclude that left ventricular myocytes of animals with low performance for exercise are smaller than animals with standard performance. In addition to that, they present losses in contractile capacity.

Moderate Continuous Aerobic Exercise Training Improves Cardiomyocyte Contractility in Β1 Adrenergic Receptor Knockout Mice

Background The lack of cardiac β1-adrenergic receptors (β1-AR) negatively affects the regulation of both cardiac inotropy and lusitropy, leading, in the long term, to heart failure (HF). Moderate-intensity aerobic exercise (MCAE) is recommended as an adjunctive therapy for patients with HF. Objective We tested the effects of MCAE on the contractile properties of left ventricular (LV) myocytes from β1 adrenergic receptor knockout (β1ARKO) mice. Methods Four- to five-month-old male wild type (WT) and β1ARKO mice were divided into groups: WT control (WTc) and trained (WTt); and β1ARKO control (β1ARKOc) and trained (β1ARKOt). Animals from trained groups were submitted to a MCAE regimen (60 min/day; 60% of maximal speed, 5 days/week) on a treadmill, for 8 weeks. P ≤ 0.05 was considered significant in all comparisons. Results The β1ARKO and exercised mice exhibited a higher (p < 0.05) running capacity than WT and sedentary ones, respectively. The β1ARKO mice showed higher body (BW), heart (HW) and left ventricle (LVW) weights, as well as the HW/BW and LVW/BW than WT mice. However, the MCAE did not affect these parameters. Left ventricular myocytes from β1ARKO mice showed increased (p < 0.05) amplitude and velocities of contraction and relaxation than those from WT. In addition, MCAE increased (p < 0.05) amplitude and velocities of contraction and relaxation in β1ARKO mice. Conclusion MCAE improves myocyte contractility in the left ventricle of β1ARKO mice. This is evidence to support the therapeutic value of this type of exercise training in the treatment of heart diseases involving β1-AR desensitization or reduction.

Physical Exercise and Regulation of Intracellular Calcium in Cardiomyocytes of Hypertensive Rats

Background Regulation of intracellular calcium (Ca2+) in cardiomyocytes is altered by hypertension; and aerobic exercise brings benefits to hypertensive individuals. Objective To verify the effects of aerobic exercise training on contractility and intracellular calcium (Ca2+) transients of cardiomyocytes and on the expression of microRNA 214 (miR-214) in the left ventricle of spontaneously hypertensive rats (SHR). Methods SHR and normotensive Wistar rats of 16 weeks were divided into 4 groups -sedentary hypertensive (SH); trained hypertensive (TH); sedentary normotensive (SN); and trained normotensive (TN). Animals of the TH and TN groups were subjected to treadmill running program, 5 days/week, 1 hour/day at 60-70% of maximum running velocity for 8 weeks. We adopted a p ≤ 0.05 as significance level for all comparisons. Results Exercise training reduced systolic arterial pressure in hypertensive rats. In normotensive rats, exercise training reduced the time to 50% cell relaxation and the time to peak contraction and increased the time to 50% decay of the intracellular Ca2+ transients. In SHR, exercise increased the amplitude and reduced the time to 50% decay of Ca2+ transients. Exercise training increased the expression of miR-214 in hypertensive rats only. Conclusion The aerobic training applied in this study increased the availability of intracellular Ca2+ and accelerated the sequestration of these ions in left ventricular myocytes of hypertensive rats, despite increased expression of miR-214 and maintenance of cell contractility.

NITRIC OXIDE AND CA2+ DYNAMICS IN CARDIOMYOCYTES: INFLUENCE OF EXERCISE CAPACITY

Introduccion: La capacidad intrinseca para el ejercicio aerobico esta relacionada con el inotropismo cardiaco. Por otro lado, todavia se desconoce la contribucion del oxido nitrico (ON) como mensajero intracelular sobre la dinamica del Ca2+ en ratones con diferentes capacidades intrinsecas para el ejercicio. Objetivo: Evaluar si el ON modula diferencialmente la variacion transitoria intracelular de Ca2+ y las liberaciones espontaneas de Ca2+ (sparks) en cardiomiocitos de ratones con diferentes capacidades intrinsecas para el ejercicio. Metodos: Ratones machos Wistar fueron seleccionados como desempeno estandar (DE) y alto desempeno (AD), de acuerdo con la capacidad de ejercicio hasta la fatiga, medida a traves del test de fuerza progresiva en la caminadora o cinta electrica. Los cardiomiocitos de los ratones fueron utilizados para determinar el transito intracelular y sparks de Ca2+ evaluados en microscopio confocal. Para estimar la contribucion del ON fue utilizado un inhibidor de sintesis del ON (L-NAME, 100 µM). Los datos fueron analizados a traves de un ANOVA two-way seguido de un post-test Tukey y presentados como promedios ± EPM. Resultados: Los cardiomiocitos de ratones AD mostraron aumento en la amplitud de la variacion transitoria de Ca2+ en comparacion con los DE. Asi mismo, el L-NAME incremento la amplitud transitoria de Ca2+ solamente en ratones DE. No se encontraron diferencias en la constante del tiempo de decaimiento de la variacion transitoria ( t ) de Ca2+ en cardiomiocitos de ratones DE e AD. Todavia, la administracion de L-NAME mostro una reduccion en el t en cardiomiocitos de ambos los grupos. Cardiomiocitos de ratones AD presentaron menor amplitud y frecuencia de sparks de Ca2+ en comparacion al grupo DE. La administracion de L-NAME incremento la amplitud de sparks de Ca2+ en cardiomiocitos del grupo AD. Conclusion: El ON modula la variacion de Ca2+ y sparks de Ca2+ en cardiomiocitos de ratones con diferentes capacidades intrinsecas para el ejercicio.

ÓXIDO NÍTRICO Y DINAMICA DE CA2+ EN CARDIOMIOCITOS: INFLUENCIA DE LA CAPACIDAD DE EJERCÍCIO

Introduccion: La capacidad intrinseca para el ejercicio aerobico esta relacionada con el inotropismo cardiaco. Por otro lado, todavia se desconoce la contribucion del oxido nitrico (ON) como mensajero intracelular sobre la dinamica del Ca2+ en ratones con diferentes capacidades intrinsecas para el ejercicio. Objetivo: Evaluar si el ON modula diferencialmente la variacion transitoria intracelular de Ca2+ y las liberaciones espontaneas de Ca2+ (sparks) en cardiomiocitos de ratones con diferentes capacidades intrinsecas para el ejercicio. Metodos: Ratones machos Wistar fueron seleccionados como desempeno estandar (DE) y alto desempeno (AD), de acuerdo con la capacidad de ejercicio hasta la fatiga, medida a traves del test de fuerza progresiva en la caminadora o cinta electrica. Los cardiomiocitos de los ratones fueron utilizados para determinar el transito intracelular y sparks de Ca2+ evaluados en microscopio confocal. Para estimar la contribucion del ON fue utilizado un inhibidor de sintesis del ON (L-NAME, 100 µM). Los datos fueron analizados a traves de un ANOVA two-way seguido de un post-test Tukey y presentados como promedios ± EPM. Resultados: Los cardiomiocitos de ratones AD mostraron aumento en la amplitud de la variacion transitoria de Ca2+ en comparacion con los DE. Asi mismo, el L-NAME incremento la amplitud transitoria de Ca2+ solamente en ratones DE. No se encontraron diferencias en la constante del tiempo de decaimiento de la variacion transitoria ( t ) de Ca2+ en cardiomiocitos de ratones DE e AD. Todavia, la administracion de L-NAME mostro una reduccion en el t en cardiomiocitos de ambos los grupos. Cardiomiocitos de ratones AD presentaron menor amplitud y frecuencia de sparks de Ca2+ en comparacion al grupo DE. La administracion de L-NAME incremento la amplitud de sparks de Ca2+ en cardiomiocitos del grupo AD. Conclusion: El ON modula la variacion de Ca2+ y sparks de Ca2+ en cardiomiocitos de ratones con diferentes capacidades intrinsecas para el ejercicio.