Comparison of the Effects of Physical Exercise, Cold Acclimation and Repeated Injections of Isoprenaline on Rat Muscle Enzymes

Abstract

The metabolic effects on rat cardiac and skeletal muscle of a strenous program of swimming, of cold acclimation and of isoprenaline treatment (0.3 mg/kg daily for 5 five-day weeks) were compared. Exercised and cold-exposed rats gained less body weight than did controls or isoprenaline-treated rats. In all treated groups the heart and the intercapular brown adipose tissue hypertrophied. The size of the adrenals increased only in isoprenaline-treated animals. Cold-acclimation and physical training increased and isoprenaline treatment reduced or did not affect the activities of succinate dehydrogenase, malate dehydrogenase and citrate synthase of cardiac muscle. In the skeletal muscle all treatments resulted in increased activities of these enzymes. Of the anaerobic enzymes analysed, only the activity of hexokinase increased in response to the treatements used. This increase was the same in cardiac as in skeletal muscle, but it was significantly greater with isoprenaline-treatment than with training or with cold-acclimation. The activities of lactate dehydrogenase and phosphofructokinase did not differ significantly. All treatments improved cold resistance, but only swimming exercise and cold acclimation significantly increased tolerance to exercise. It is concluded that prolonged stimulation of adrenergic beta-receptors by catecholamines is responsible for the metabolic changes observed.

Effects of selective and nonselective beta-adrenergic blockade on mechanisms of exercise conditioning.

“…Heart rate decreased during several levels of submaximal exercise after training in both drug groups (p < .05, figure 3), and there were no significant differences between the atenolol and nadolol groups. The decreases in heart rate during submaximal workloads were significantly greater in the placebo group than in either of the drug groups (p < .05, figure 3); for example, at 60% VO2max (stage 4) the placebo group had a 17 beats/min reduction in heart rate, whereas both drug groups had an 8 reduction. Perceived exertion score and heart rateblood pressure product decreased significantly during submaximal exercise in both drug groups (p < .05), whereas oxygen pulse and respiratory exchange ratio did not change (table 4).…”

Effects of exposure to cold on metabolic characteristics in gastrocnemius muscle of frog (Rana pipiens).

“…Oxidative enzyme activities of skeletal muscles increased in winter and by cold acclimation (Harri & Valtora, 1975;Matoba & Murakami, 1981;Wickler, 1981, Marsh & Dawson, 1982, although citrate synthase activity did not change in one study (Marsh & Dawson, 1982). Yahata & Kuroshima (1977) found enlargement of muscle mitochondria and development of cristae in cold-acclimated rats.…”

Enzymatic adaptation to physical training under beta-blockade in the rat. Evidence of a beta 2-adrenergic mechanism in skeletal muscle.

“…Based upon the observation that chronic activation of the sympathoadrenergic system alone, as produced by cold acclimation, repeated heat exposure, or long-term injection of the ,B-adrenergic stimulant isoprenaline, could induce the activities of oxidative enzymes in skeletal muscle (2,3), some physiologists believe that functional adrenoceptors are necessary for a metabolic adaptation of physical training. This hypothesis has received support from the observations that morphologic and enzymatic adaptation in heart and skeletal muscle did not take place either in sympathectomized rats (4), or in rats receiving a ,B-adrenoceptor antagonist, propranolol (5).…”