Lack of effect of running training at two intensities on cardiac myosin isozyme composition in rats.

Little information is available regarding the influence of the intensity of endurance training over biochemical profiles in cardiac muscle. We assessed the effect of running training at two different intensities on cardiac myosin isozyme composition in rats. Male Sprague-Dawley rats (4 weeks old) were divided into four groups: sedentary control (SC), trained at 20 m/min (T20), trained at 40 m/min (T40), and weight-matched sedentary control (WMSC) groups. The T20 and T40 group rats were trained by treadmill running for 60 min/d, 5 d/week at 20 or 40 m/min, respectively, for 11 to 12 weeks. In both groups the left ventricle was significantly heavier than in WMSC animals. The ratio of left ventricle weight to body weight was significantly greater in T40 rats than in either the untrained (SC and WMSC) or trained T20 rats. Thus the extent of exercise-induced cardiac hypertrophy appears to be influenced by the intensity of running training. However, neither of the training programs (1) induced a change in cardiac myosin isozyme composition or (2) had any effect on myocardial succinate dehydrogenase or citrate synthase activity. These results suggest that although the intensity of running training may play an important role in cardiac morphological adaptation, it does not modulate the cardiac biochemical adaptation to running training.

Spaceflight effects on beta-adrenoceptor and metabolic properties in rat plantaris.

Effects of 14 days of spaceflight on beta-adrenoceptor (beta-AR), mitochondrial enzyme activities, and fiber type composition were studied in plantaris muscles of male adult Sprague-Dawley rats. The beta-AR was analyzed in cross sections by quantitative autoradiography. The maximum binding capacity (Bmax) of beta-AR was significantly lowered (approximately 29%) after flight, but the recovery was not completed within 9 days in 1-G environment. Because the dissociation constant remained unchanged, it is suggested that the changes in the Bmax were caused by the alteration of receptor number. The activities of succinate dehydrogenase (SDH) measured in whole homogenates were subnormal (approximately -24%) in muscles sampled approximately 5 h after flight but they were normalized during 9 days of recovery. The percent composition of fiber types and beta-hydroxyacyl CoA dehydrogenase (HAD) activity did not change significantly due to spaceflight. It is suggested that the spaceflight-induced decrease of the Bmax of beta-AR in plantaris was accompanied by a lowered activity of a mitochondrial inner-membrane enzyme SDH but not a matrix enzyme HAD.

Effects of chronic iron deficiency anemia on brain metabolism.

The effects of chronic iron deficiency anemia on brain (cortex) metabolism were estimated by 31P-nuclear magnetic resonance spectroscopy and biochemical analyses in male Wistar rats. Iron deficiency anemia was induced by supplying diet containing either approximately 2 or approximately 6 ppm Fe. Control diet was supplemented with 100 ppm Fe as ferric citrate. After 8-9 weeks, blood hemoglobin levels were approximately 13, 5, and 3 g/100 ml in the 100 ppm, 6 ppm, and 2 ppm Fe group, respectively. The blood lactate levels at rest in these groups were approximately 3, 5, and 6 mM. The blood glucose concentration also tended to be elevated in iron-deficient rats. The high-energy phosphate contents in brain were not affected by iron deficiency. The activities of succinate dehydrogenase and cytochrome oxidase per unit protein in the 2 ppm Fe group were significantly less than in the 100 ppm Fe group, but those activities were not significantly affected by feeding diet with 6 ppm Fe. The activities of lactate dehydrogenase in iron-deficient group tended to be elevated but not significantly. The activities of non-iron containing mitochondrial enzymes, citrate synthase and beta-hydroxyacyl CoA dehydrogenase, were unchanged. It is suggested that the brain has a higher tolerance to iron deficiency than skeletal muscle in terms of the metabolic characteristics, although this may be associated with a lower level of neural activity.

Metabolic adaptation of skeletal muscles to gravitational unloading.

Responses of high-energy phosphates and metabolic properties to hindlimb suspension were studied in adult rats. The relative content of phosphocreatine (PCr) in the calf muscles was significantly higher in rats suspended for 10 days than in age-matched cage controls. The Pi/PCr ratio, where Pi is inorganic phosphate, in suspended muscles was less than controls. The absolute weights of soleus and medial gastrocnemius (MG) were approximately 40% less than controls. Although the % fiber distribution in MG was unchanged, the % slow fibers decreased and the % fibers which were classified as both slow and fast was increased in soleus. The activities (per unit weight or protein) of succinate dehydrogenase and lactate dehydrogenase in soleus were unchanged but those of cytochrome oxidase, beta-hydroxyacyl CoA dehydrogenase, and citrate synthase were decreased following unloading. None of these enzyme activities in MG changed. However, the total levels of all enzymes in whole muscles decreased by suspension. It is suggested that shift of slow muscle toward fast type by unloading is associated with a decrease in mitochondrial biogenesis. Further, gravitational unloading affected the levels of muscle proteins differently even in the same mitochondrial enzymes.