Cardiac and skeletal muscle adaptations to voluntary wheel running in the mouse

Abstract

In this paper, we describe the effects of voluntary cage wheel exercise on mouse cardiac and skeletal muscle. Inbred male C57/Bl6 mice (age 6-8 wk; n = 12) [corrected] ran an average of 4.3 h/24 h, for an average distance of 6.8 km/24 h, and at an average speed of 26.4 m/min. A significant increase in the ratio of heart mass to body mass (mg/g) was evident after 2 wk of voluntary exercise, and cardiac atrial natriuretic factor and brain natriuretic peptide mRNA levels were significantly increased in the ventricles after 4 wk of voluntary exercise. A significant increase in the percentage of fibers expressing myosin heavy chain (MHC) IIa was observed in both the gastrocnemius and the tibialis anterior (TA) by 2 wk, and a significant decrease in the percentage of fibers expressing IIb MHC was evident in both muscles after 4 wk of voluntary exercise. The TA muscle showed a greater increase in the percentage of IIa MHC-expressing fibers than did the gastrocnemius muscle (40 and 20%, respectively, compared with 10% for nonexercised). Finally, the number of oxidative fibers as revealed by NADH-tetrazolium reductase histochemical staining was increased in the TA but not the gastrocnemius after 4 wk of voluntary exercise. All results are relative to age-matched mice housed without access to running wheels. Together these data demonstrate that voluntary exercise in mice results in cardiac and skeletal muscle adaptations consistent with endurance exercise.

Intensity-controlled treadmill running in mice: cardiac and skeletal muscle hypertrophy

“…In the present study, ventricular weights increased more than previously reported in mice and about the same as in rats exercising for 7 wk with the same regimen (42). Other studies in mice report no change (31) or an increase between 10 and 15% in cardiac mass (1,24), after 4 wk of training in C57BL/6J mice, treadmill, voluntary wheel, and swimming exercise, respectively. These studies lack a rigorous control of exercise intensity, and cardiovascular load seemed lower.…”

“…Males had larger extensor digitorum longus muscles, but soleus muscle weight was similar. Other studies report varying results: 20-24% increased (39) and unchanged (1,19) skeletal muscle mass, and increased cross-sectional area (19,33) and GATA-2 expression (hypertrophy marker), after 4-12 wk of training (19,33). Interestingly, skeletal muscle growth occurs in mice in response to endurance training, contrary to observations in humans (4).…”

“…3, allometric scaling greatly enhances comparison of V O 2 in animals with different weights. Reports of long-term running in mice have reported decreased (34,40,44) or unchanged (1,19,31,33,37,39) body mass, whereas swimming yielded an increase (24). In a survey of 100 recent transgenic mice studies at PubMed, body mass ranged between 17 and 74 g and age between 26 days and 12 mo.…”

“…Exercise capacity and adaptations have also been measured indirectly, e.g., as maximal exercise duration and total distance run (26). A 4-wk regimen led to 15% increased cardiac mass as well as increased expression of hypertrophy markers, i.e., atrial and brain natriuretic peptides, by 74 and 52%, respectively (1). Myosin heavy chain redistribution toward greater expression of type IIa and IId/x occurred, whereas skeletal muscle weights remained unchanged.…”

Rôles de PPARδ dans la physiologie du muscle squelettique

“…Ces observations ont été confirmées très récem-ment par un autre groupe qui montre, en outre, que la surexpression musculaire de PPARδ confère une protection très efficace contre les effets néfastes des régimes riches en lipides, comme l'obé-sité et la résistance à l'insuline, et augmente la résistance à la fatigue musculaire [5]. Ainsi, les animaux qui surexpriment PPARδ dans leurs muscles acquiè-rent un phénotype musculaire et méta-bolique similaire au phénotype « marathonien » induit par l'entraînement d'endurance de longue durée [6]. Cela est tout à fait inattendu, puisque ces animaux ont une activité physique qui n'est pas perturbée.…”