Ventricular remodeling induced by retinoic acid supplementation in adult rats

Retinoic acid (RA) plays a role in regulating cardiac geometry and function throughout life. The aim of this study was to analyze the cardiac effects of RA in adult rats. Wistar rats were randomly allocated to a control group (n = 18) receiving standard rat chow and a group treated with RA (n = 14) receiving standard rat chow supplemented with RA for 90 days. All animals were evaluated by echocardiography, isolated papillary muscle function, and morphological studies. Whereas the RA-treated group developed an increase in both left ventricular (LV) mass and LV end-diastolic diameter, the ratio of LV wall thickness to LV end-diastolic diameter remained unchanged when compared with the control group. In the isolated papillary muscle preparation, RA treatment decreased the time to peak developed tension and increased the maximum velocity of isometric relengthening, indicating that systolic and diastolic function was improved. Although RA treatment produced an increase in myocyte cross-sectional area, the myocardial collagen volume fraction was similar to controls. Thus our study demonstrates that small physiological doses of RA induce ventricular remodeling resembling compensated volume-overload hypertrophy in rats.

Thyroid State and Tolerance of Mammalian Myocardium to Hypoxia

Thyroid hormone is known to affect myocardial glycogen stores and thereby possibly limit anaerobic performance of mammalian cardiac muscle. Thyroid hormone administration (3,5,T-triiodo-L-thyroxine, 300 mu g/kg/day, sc) for 10 days decreased left ventricle (LV) glycogen concentration relative to euthyroid animals (2.78 +/- 0.46 vs. 4.28 +/- 0.29 mg/g of LV (mean +/- SEM)) while increasing the percent of V(1) myosin isozyi-ne, contractile activity and cardiac mass. In contrast, thyroidectomy increased myocardial glycogen stores (8.50 +/- 0.56 mg/g of LV) and shifted the myosin isozyme toward V(3), prolonged contractile activity and decreased LV mass. Thyroxine administration for 3, 7 and 10 days to thyroidectomized animals progressively decreased contractile duration and increased LV mass. Thyroxine administration for 3 or 7 days to thyroidectomized rats did not reduce glycogen stores (7.75 +/- 1.02 and 9.62 +/- 1.16 mg/g of LV, respectively), whereas myocardial glycogen declined to 3.30 +/- 0.58 mg/g of LV after 10 days of treatment. During hypoxia, cardiac muscle from thyroidectomized rats maintained greater active force and developed less contracture relative to euthyroid and, to a greater extent, than hyperthyroid rats. Removal of glucose from the bath decreased anaerobic performance and impaired recovery; however, myocardium from thyroidectomized rats remained more tolerant to hypoxia than the euthyroid group. Overall, the intrinsic LV glycogen content was positively correlated to anaerobic performance. These data demonstrate that the thyroid state profoundly affects myocardial growth, contractility and anaerobic performance of rat myocardium. Although energy demand may affect function during hypoxia, anaerobic substrate reserve (cardiac glycogen concentration) appears to be the primary factor determining tolerance to hypoxic stress. J. Exp. Zool. 311A:399-407, 2009. (C) 2009 Wiley-Liss, Inc.

Collagen and reticular fibers in left ventricular muscle in diabetic rats: Physical exercise prevents its changes?

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Participação do Estado Contrátil e do Relaxamento Miocárdico na Disfunção Ventricular durante a Transição Hipertrofia-Falência Cardíaca

Purpose - To investigate the participation of contractile state and relaxation in cardiac muscle dysfunction during the transition from stable hypertrophy to cardiac decompensation in aging spontaneously hypertensive rats (SHR). Methods - isolated left ventricular papillary muscle function was studied in SHR with heart failure (SHR-F), in age-matched SHR without evidence of heart failure (SHR-NF), and in nonhypertensive controls Wistar-Kyoto rats (WKY). Muscles were analised in isometric and isotonic contractions in Krebs-Henseleit solution with calcium concentration of 1.25mM at 28°C. Results - Papillary muscles from SHR-F and SHR-NF demonstrated decreased active tension development and shortening velocity relative to normotensive WKY (p<0.05). SHR-F and SHR-NF did not differ. Compared with SHR-NF and WKY, muscle passive stiffness was increased in the failing SHR (p<0.05 versus WKY and SHR-NF). This parameter did not differ between SHR-NF and WKY (p> 0.05). Conclusion - These data suggest that the progression from stable hypertrophy to heart failure is associated with changes in the passive stiffness and is not related to depression of myocardial contractile function.

Cellular and molecular mechanisms of apoptosis in skeletal muscle atrophy

Apoptosis is necessary for maintaining the integrity of proliferative tissues, such as epithelial cells of the gastrointestinal and integumentary systems. The role of apoptosis in post-mitotic tissues, such as skeletal muscle, is less well defined, but several lines of evidence suggest that it occurs in both myofiber and other interstitial muscle cell types. Apoptosis of myonuclei likely contributes to the loss of muscle mass, but the mechanisms underlying this process are largely unknown. Caspase-dependent as well as caspase-independent pathways have been implicated, and the mode by which atrophy is induced likely determines the apoptotic mechanisms that are utilized. It remains to be determined whether a decrease in apoptosis will alleviate atrophy and distinct research strategies may be required to clarify the different causes of skeletal muscle mass loss. In this review, it was also speculated that apoptosis is a normal regulatory process that the myofiber can use to reduce the number of nuclear domains, thus ensuring optimal cell functions according to the mechanical load imposed on the muscle. ©FUNPEC-RP.

A comparative study of myocardial function and morphology during fasting/refeeding and food restriction in rats

Background: This study compared the influence of fasting/refeeding cycles and food restriction on rat myocardial performance and morphology. Methods: Sixty-day-old male Wistar rats were submitted to food ad libitum (C), 50% food restriction (R50), and fasting/refeeding cycles (RF) for 12 weeks. Myocardial function was evaluated under baseline conditions and after progressive increase in calcium and isoproterenol. Myocardium ultrastructure was examined in the papillary muscle. Results: Fasting/refeeding cycles maintained rat body weight and left ventricle weight between control and food-restricted rats. Under baseline conditions, the time to peak tension (TPT) was more prolonged in R50 than in RF and C rats. Furthermore, the maximum tension decline rate (-dT/dt) increased less in R50 than in RF with calcium elevation. While the R50 group showed focal changes in many muscle fibers, such as the disorganization or loss of myofilaments, polymorphic mitochondria with disrupted cristae, and irregular appearance or infolding of the plasma membrane, the RF rats displayed few alterations such as loss or disorganization of myofibrils. Conclusion: Food restriction promotes myocardial dysfunction, not observed in RF rats, and higher morphological damage than with fasting/refeeding. The increase in TPT may be attributed possibly to the disorganization and loss of myofibrils; however, the mechanisms responsible for the alteration in -dT/dt in R50 needs to be further clarified. © 2010 Elsevier Inc. All rights reserved.

The effect of muscle fatigue on the last stride before stepping down a curb

The stride before landing may be important during stepping down. The aim of this study was to analyze variability of the kinematics and muscle activity in the final stride before stepping down a curb, with and without ankle and knee muscle fatigue. Ten young participants walked at self-selected speed and stepped down a height difference (10-cm) in ongoing gait. Five trials were performed before and after a muscle fatigue protocol (one day: ankle muscle fatigue, another day: knee muscle fatigue). The analysis focused on the trailing leg during the last but one and the last step on the higher level. Kinematics and muscle activity were recorded. Fatigue increased variability of foot-step horizontal distance in the last step on the higher level of the trailing limb, as well as in the first steps on the lower level for both limbs. This appeared due to an increase in the range of motion of the knee joint after both fatigue protocols. Participants additionally showed an increased ankle and hip ROM and decreased knee ROM. Our results suggest a loss of control under fatigue reflected in a higher variability of trailing and leading limb-step horizontal distances, with compensatory changes to limit fatigue effects, such as a redistribution of movement over joints. © 2012 Elsevier B.V.

Função cardíaca em cães com Diabetes Mellitus

Pós-graduação em Medicina Veterinária - FCAV

Influência do aumento energético proveniente de dieta hiperlipídica na disfunção cardíaca em ratos com estenose aórtica supravalvar: participação das cadeias pesadas de miosina e da bomba de cálcio do retículo sarcoplasmático

Pós-graduação em Fisiopatologia em Clínica Médica - FMB

Evolution and genomic organization of muscle microRNAs in fish genomes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cardiovascular Complications following Chronic Treatment with Cocaine and Testosterone in Adolescent Rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeitos da imersão em água fria na recuperação pós-exercício: análise conjunta de parâmetros clínicos, funcionais, metabólico e autonômico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of Statin and Aerobic Physical Exercise Association in the Cardiomyocytes of the Rat. Morphometric Study

Physical exercise and statins, recommended interventions to dyslipidaemia treatment, are independently related to cardiomyocytes alterations, characterized by miocardic hypertrophy and apoptosis, respectively. Thus, the objective of the present study was to analyze the effects of statin and aerobic physical exercise association in the morphometric parameters of cardiac cell nucleus. 40 male rats adults were divided into four groups: exercised (DE); sedentary (DS), exercised and statin use (DES); sedentary and statin use (DSS). The animals received during the whole experimental period a hiperlipidic diet added 20% of coconut oil and 1.25% of cholesterol; after 30 days of its ingestion, a blood collection was made to verify the dyslipidaemia. Simvastatin (20 mg) was taken five days a week, during eight weeks. During this period, the animals exercised 60 minutes daily in the treadmill. After the last day of the protocol, the cardiac muscle was collected and maintained in liquid nitrogen (-180 degrees C); the cuts were stained by Hematoxilin-Eosin method, and the cardiac fibers were submitted to the nuclear morphometric analyses. The data were analyzed using descriptive analyses, paired T test, Kruskal-Wallis test and Dunn post hoc test; for all analyses, it was adopted p<0.05. It was verified that the group receiving statin presented values statistically significant in comparison to the other groups, in the tridimensional and linear variables. The exercised and statin group, the values obtained in the morphometric analyses were similar to the control group. It is suggested that statins alone can cause alterations in the nucleus of cardiac cells that can be related to apoptosis occurrence and, when exercise is practiced associated to statin administration, the effects of statin can be reduced, what can be related to beneficial adaptations of cardiac mitochondrial in response to physical exercise, turning them more resistant to apoptotic stimuli.

Food restriction induces in vivo ventricular dysfunction in spontaneously hypertensive rats without impairment of in vitro myocardial contractility

Cardiac structures, function, and myocardial contractility are affected by food restriction (FR). There are few experiments associating undernutrition with hypertension. The aim of the present study was to analyze the effects of FR on the cardiac response to hypertension in a genetic model of hypertension, the spontaneously hypertensive rat (SHR). Five-month-old SHR were fed a control or a calorie-restricted diet for 90 days. Global left ventricle (LV) systolic function was evaluated in vivo by transthoracic echocardiogram and myocardial contractility and diastolic function were assessed in vitro in an isovolumetrically beating isolated heart (Langendorff preparation). FR reduced LV systolic function (control (mean ± SD): 58.9 ± 8.2; FR: 50.8 ± 4.8%, N = 14, P < 0.05). Myocardial contractility was preserved when assessed by the +dP/dt (control: 3493 ± 379; FR: 3555 ± 211 mmHg/s, P > 0.05), and developed pressure (in vitro) at diastolic pressure of zero (control: 152 ± 16; FR: 149 ± 15 mmHg, N = 9, P > 0.05) and 25 mmHg (control: 155 ± 9; FR: 150 ± 10 mmHg, N = 9, P > 0.05). FR also induced eccentric ventricular remodeling, and reduced myocardial elasticity (control: 10.9 ± 1.6; FR: 9.2 ± 0.9%, N = 9, P < 0.05) and LV compliance (control: 82.6 ± 16.5; FR: 68.2 ± 9.1%, N = 9, P < 0.05). We conclude that FR causes systolic ventricular dysfunction without in vitro change in myocardial contractility and diastolic dysfunction probably due to a reduction in myocardial elasticity.

Quantidade de gordura no músculo levantador da pálpebra de portadores de ptose congênita

OBJETIVO: Quantificar a gordura presente no músculo levantador da pálpebra de portadores de ptose congênita, correlacionando este achado com fatores clínico-epidemiológicos desta afecção. MÉTODOS: Vinte e duas amostras de músculo levantador da pálpebra superior, provenientes de portadores de ptose congênita, foram avaliadas morfometricamente, com o intuito de quantificar a gordura presente nos espécimes e correlacionar este achado com características como idade, sexo, grau de ptose e função do músculo levantador. RESULTADOS: Não houve correlação entre a quantidade de gordura encontrada no músculo levantador de portadores de ptose congênita e os dados clínicos dos pacientes estudados. CONCLUSÃO: A quantidade de gordura presente no músculo levantador da pálpebra superior, nas condições do presente estudo, não está associada com idade, sexo, grau de ptose ou função do músculo levantador. Novos estudos serão necessários para avaliar a real alteração que ocorre no músculo levantador da pálpebra de indivíduos com ptose palpebral.