R.J. Barnard

Properties of immobilized hind-limb muscles of the Galago senegalensis.

Abstract Morphological, biochemical, and physiological properties of longterm (6 mo) immobilized skeletal muscles of a nonhuman primate were studied in seven Galago senegalensis which were immobilized at the ankle and knee of one hind limb with an external brace. Electromyographic activity of the ipsilateral and contralateral quadriceps and muscles of the calf were assessed after 5 and 6 mo of immobilization. The EMG was markedly reduced in the immobilized muscles compared to the contralateral control when the brace was intact and the animal moving freely. Without exception, extensor muscles atrophied more than flexors. The soleus, a slow-twitch muscle atrophied more than any other muscle of the lower leg but the same was not true of the vastus intermedius the analogous muscle of the thigh. Slow-twitch oxidative fibers (SO) were atrophied more than fast-twitch oxidative glycolytic fibers (FOG), and FOG tended to atrophy more than fast-twitch glycolytic fibers (FG). The immobilized soleus and vastus intermedius had a smaller percentage of SO fibers than their controls, suggesting that they had faster contraction times. With respect to alterations in reduced nicotinamide adenine dinucleotide diaphorase activity, no consistent pattern was observed except for a greater coarseness of staining granules and more homogeneous dispersion of the granules throughout the cross-section of the fibers. No changes were found in phosphorylase, lactate dehydrogenase, or succinate dehydrogenase specific activity or in myoglobin concentration in homogenates of ankle flexors or the vastus lateralis. Myosin ATPase, but not actomyosin ATPase activity was significantly less in the immobilized gastrocnemius-plantaris muscles. No change in contractile properties related to speed were observed in the plantaris. This muscle did exert more twitch and tetanic tension per gram of muscle in the immobilized leg.

Work capacity, heart rate and blood lactate responses to iron treatment.

Summary. Changes in haemoglobin (Hb), work performance, heart rate and postexercise blood lactate were studied in iron deficient, anaemic subjects for 16 d following total dosage infusion of iron dextran, i.v. (30–50 ml). Six adult men and 14 women were subjects with initial Hb levels of 6.6±0.6 g/dl (mean±SEM) for the iron treatment group (n=10) and 8.0±0.7 for the placebo group (saline infusion, n=10). Serum iron levels were 0.51±0.15 and 0.67±0.12 mg/l for the two groups, respectively. Haemoglobin and maximal work time increased significantly within 4 d after iron treatment and continued to increase up to 16 d. No changes were found in the placebo subjects. Heart rates at a given exercise intensity were lower in the iron treatment group than in control subjects who had the same Hb levels but had not been treated with iron. Post‐exercise venous blood lactate was similar on succeeding days after iron treatement even though the subjects reached higher work loads.

Overloaded skeletal muscles of a nonhuman primate (Galago senegalensis)

Abstract Selected morphological, biochemical, and physiological properties of skeletal muscles from five control and six trained adult nonhuman primates, Galago senegalensis , were studied. After a 6-month treadmill endurance-training program, fewer glycogen-depleted fibers were found in the plantaris of trained than in controls after 15 min of electrical stimulation. There was an increase in the proportion of fast-twitch oxidative-glycolytic fibers at the expense of fast-twitch glycolytic fibers, enhanced cytochrome a and c concentrations, and elevated SDH activity. No changes in glycolytic enzymes or contraction time of the normally fast-twitch plantaris muscle were found. Maximal twitch and tetanic muscle tension and overall fiber size were not significantly different in the controls and trained Galagos. However, fast-twitch oxidative-glycolytic fibers in the plantaris were significantly larger in the trained Galagos. These adaptations were muscle specific, demonstrating that muscles vary in response to treadmill exercise depending on anatomical location or action (or both) in the exercise as well as fiber-type composition.

Lactate dehydrogenase isoenzymes: Distribution in fast-twitch red, fast-twitch white, and slow-twitch intermediate fibers of guinea pig skeletal muscle

Abstract Lactate dehydrogenase activity and LDH isoenzyme distribution were determined in supernatants of skeletal muscles consisting predominately of fast-twitch red, fast-twitch white, or slow-twitch intermediate fibers. The LDH activity was highest in the fast-twitch white. The activity in the fast-twitch red was significantly lower than in the fast-twitch white but significantly greater than in slow-twitch intermediate muscle or the heart. LDH5 was found to be the predominant isoenzyme in both the fast-twitch white and fast-twitch red fibers whereas LDH1 predominated in both the slow-twitch intermediate fibers and the heart.

The neuromuscular junction in response to endurance training

Endplate and nonendplate cholinesterase and choline acetyltransferase activities were measured in muscles of untrained and endurance-trained rats to determine the relationship of these enzymes to known physiologic and morphologic properties of specific types of muscle fibers, and to determine the responsiveness of these presynaptic and postsynaptic enzymes to chronic muscular activity. In the trained soleus and red and white vastus lateralis, endplate cholinesterase activity was significantly (P < 0.05) higher in the trained than in the nontrained endplate region of the white vastus lateralis muscle only. Endplate cholinesterase activities were greater than nonendplate values in both trained and untrained muscles. Choline acetyltransferase activity in soleus and red and white vastus lateralis was not affected significantly by endurance training. The selective training effect on the cholinesterase activity of the fast-twitch glycolytic fibers contrasts with the small change in oxidative metabolism in fast-twitch glycolytic fibers previously reported in endurance-trained rats.

Distribution of acid hydrolases in guinea pig skeletal muscle.

Abstract The activity of five acid hydrolases was determined in the homogenates of skeletal muscle consisting of predominantly fast-twitch red, fast-twitch white or slow-twitch intermediate fibers in normal guinea pigs. The specific activities of arylsulfatase A, β-acetylglucosaminidase, β-galactosidase, acid cathepsin and acid phosphatase were found to be highest in the slow-twitch intermediate, medium in the fast-twitch red and lowest in the fast-twitch white fibers. These data provide additional biochemical characteristics of the various types of fibers which constitute guinea pig skeletal muscle.