Age-related differences in effect of exercise training on cardiac muscle function in rats

Moderate intensity, but not high intensity, treadmill exercise training alters power output properties in myocardium from aged rats

Aging is characterized by a progressive decline in cardiac function, but endurance exercise training has been shown to retard a number of deleterious effects of aging. However, underlying mechanisms by which exercise training improves age-related decrements in myocardial contractile function are not well understood. The purpose of this study was to determine the effects of exercise training on power output properties in permeablized (skinned) myocytes of old rats. Thirty-month-old rats were divided into sedentary control (C) and groups undergoing 11 weeks of treadmill exercise training at moderate intensity (MI) and at high intensity (HI). Peak power output normalized to maximal force was significantly increased in MI but not in HI compared to C with significant increases in atrial myosin light chain 1 in ventricle. These results suggest that MI exercise training is beneficial as a significant increase was seen in the ability of the myocardium to do work, but this effect was not seen with HI training.

Social determinants of physical exercise in older men in Jamaica

Background:

Background: Physical activity interventions have been demonstrated to improve health-related quality of life and to be of special benefit to older adults with specific chronic conditions including arthritis, hypertension, diabetes mellitus, and heart disease.

Aim:

This study examined the extent and social determinants of physical exercise in elderly men in Jamaica.

Materials and Methods:

A sample of 2,000 men 55 years of age and older was extracted from a total of 33,674 males in the parish of St. Catherine. A 132-item questionnaire was used to collect the data. A stratified random sampling technique was used to draw the sample. Descriptive statistics were used to provide background information on the sub-sample, and logistic regressions were utilized to model physical exercise.

Results:

Of the respondents, 55.4% indicated good health status, 51.0% lived in rural areas; 10.4% had moderate to high functional dependence and 67.3% reported that they did some form of physical exercise. Of those who indicated involvement in physical exercise (n = 1,345), 77.2% jogged, ran, and/or walked; 13.3% did aerobics; 4.7% swam; 2.0% cycled and 0.6% did push-ups or sit-ups. The variables that predicted being engaged in physical exercise were education; age of respondents; current good health status; household head; health plan; employment status, and social support.

Conclusion:

Most of the elderly men were engaged in some form of physical activity and had good health. Age and good health status were the most influential social determinants of physical exercise. However, effective interventions to promote physical activity in older men in Caribbean countries such as Jamaica deserve wide implementation.

Effects of short-term treadmill exercise training or growth hormone supplementation on diastolic function and exercise tolerance in old rats

Whether the lusitropic potential of short-term exercise in aged rats is linked to an augmentation in the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis and an alteration in the cardiac renin angiotensin system (RAS) is unknown. Old (28-month-old) male, Fischer 344xBrown Norway rats were randomized to 4 weeks of GH supplementation (300 microg subcutaneous, twice daily) or 4 weeks of treadmill running, or were used as sedentary controls. Six-month-old rats, sedentary or exercised, were used as young controls. Training improved exercise capacity in old animals. Exercise and GH attenuated age-related declines in myocardial relaxation despite an exercise-induced suppression of IGF-1. The regulatory protein, sarcoplasmic Ca2+ adenosine triphosphatase (SERCA2), increased with exercise but not GH. Among aged rats, the cardiac RAS was not altered by training or GH. Thus, the signaling pathway underlying the lusitropic benefit of short-term habitual exercise in the aged rat may be distinct from GH-mediated benefits and independent of the cardiac RAS.

Swimming exercise in infancy has beneficial effect on the hearts in cardiomyopathic Syrian hamsters

The phenotypic expression of cardiomyopathy is greatly influenced by extrinsic factors other than intrinsic genetic defects, such as environmental stress. Exercise is assumed to be an important extrinsic factor, since sudden death is sometimes seen during exercise in young patients with hypertrophic cardiomyopathy (HCM). However, the long-term effects of mild exercise on phenotypic expression in cardiomyopathy remain unclear. To evaluate the effects of exercise performed during infancy or adolescence in cardiomyopathic patients, cardiomyopathic Syrian hamsters (BIO14.6) were subjected to swimming. BIO14.6 and age-matched congenic normal hamsters (CN) as controls were divided into three groups: sedentary (Sed), and trained during infancy (Inf) and during adolescence (Ado). Histological and biochemical analysis of 41-week-old hamsters revealed that (1) the relative level of beta-myosin heavy chain mRNA was significantly lower in the Inf group than in the Sed and Ado groups of BIO14.6. The level in the Inf group of BIO14.6 was compatible with that in the age-matched Sed group of the CN strain; (2) in BIO14.6, degenerative mitochondrial change in the cardiomyocytes was not seen in the Inf group while it was common in the Sed and Ado groups; (3) calcineurin phosphatase activity in the swimming group in 10-week-old CN was significantly higher than that of the age-matched sedentary group, and was as much as that of the swimming and sedentary groups in 10- and 41-week-old BIO14.6.

Exercise training improves cardiac function-related gene levels through thyroid hormone receptor signaling in aged rats

Exercise training improves the aging-induced downregulation of myosin heavy chain (MHC) and sarcoplasmic reticulum (SR) Ca(2+)-ATPase, which participate in the regulation of cardiac contraction and relaxation. Thyroid hormone receptor (TR), a transcriptional activator, affected the regulation of gene expression of MHC and SR Ca(2+)-ATPase. We hypothesized that myocardial TR signaling contributes to a molecular mechanism of exercise training-induced improvement of MHC and SR Ca(2+)-ATPase genes with cardiac function in old age. We investigated whether TR signaling and gene expression of MHC and SR Ca(2+)-ATPase in the aged heart are affected by exercise training, using the hearts of sedentary young rats (4 mo old), sedentary aged rats (23 mo old), and trained aged rats (23 mo old, swimming training for 8 wk). Trained aged rats showed improvement in cardiac function. Expression of TR-alpha1 and TR-beta1 proteins in the heart were significantly lower in sedentary aged rats than in sedentary young rats and were significantly higher in trained aged rats than in sedentary aged rats. The activity of TR DNA binding to the transcriptional regulatory region in the alpha-MHC and SR Ca(2+)-ATPase genes and the mRNA and protein expression of alpha-MHC and SR Ca(2+)-ATPase in the heart and plasma 3,3'-triiodothyronine and thyroxine levels were altered in association with changes in the myocardial TR protein levels. These findings suggest that exercise training improves the aging-induced downregulation of myocardial TR signaling-mediated transcription of MHC and SR Ca(2+)-ATPase genes, thereby contributing to the improvement of cardiac function in trained aged hearts.

Influence of age and run training on cardiac Na+/Ca2+ exchange

Effects of age and training on myocardial Na+/Ca2+ exchange were examined in young sedentary (YS; 14-15 mo), aged sedentary (AS; 27-31 mo), and aged trained (AT; 8- to 11-wk treadmill run training) male Fischer Brown Norway rats. Whole heart performance and isolated cardiocyte Na+/Ca2+ exchange characteristics were measured. At the whole heart level, a small but significant slowing of late isovolumic left ventricular (LV) relaxation, which may be indicative of altered Na+/Ca2+ exchange activity, was seen in hearts from AS rats. This subtle impairment in relaxation was not observed in hearts from AT rats. At the single-cardiocyte level, late action potential duration was prolonged, resting membrane potential was more positive, and overshoot potential was greater in cardiocytes from AS rats than from YS rats (P < 0.05). Training did not influence any of these age-related action potential characteristics. In electrically paced cardiocytes, neither shortening nor intracellular Ca2+ concentration ([Ca2+]i) dynamics was influenced by age or training. Similarly, neither age nor training influenced the rate of [Ca2+]i clearance via forward (Nain+ /Caout2+) Na+/Ca2+ exchange after caffeine-induced Ca2+ release from the sarcoplasmic reticulum or cardiac Na+/Ca2+ exchanger protein (NCX1) expression. However, when whole cell patch-clamp techniques combined with fluorescence microscopy were used to evaluate the ability of Na+/Ca2+ exchange to alter cytosolic [Ca2+] ([Ca2+]c) under conditions where membrane potential (Vm) and internal and external [Na+] and [Ca2+] could be controlled, we observed age-associated increases in forward Na+/Ca2+ exchange-mediated [Ca2+]c clearance (P < 0.05) that were not influenced by training. The age-related increase in forward Na+/Ca2+ exchange activity provides a hypothetical explanation for the late action potential prolongation observed in this study.

Effects of exercise training on cardiac function, gene expression, and apoptosis in rats

This study determined the effects of exercise training on cardiac function, gene expression, and apoptosis. Rats exposed to a regimen of treadmill exercise for 13 wk had a significant increase in cardiac index and stroke volume index and a concomitant decrease in systemic vascular resistance compared with both age-matched and body weight-matched sedentary controls in the conscious state at rest. In exercise-trained animals, there was no change in the expression of several marker genes known to be associated with pathological cardiac adaptation, including atrial natriuretic factor, beta-myosin heavy chain, alpha-skeletal and smooth muscle actins, and collagens I and III. Exercise training, however, produced a significant induction of alpha-myosin heavy chain, which was not observed in rats with myocardial infarction. No histological features of cardiac apoptosis were observed in the treadmill-trained rats. In contrast, apoptotic myocytes were detected in animals with myocardial infarction. In summary, exercise training improves cardiac function without evidence of cardiac apoptosis and produces a pattern of cardiac gene expression distinct from pathological cardiac adaptation.