Summary
After 10 weeks of treadmill training, female Sprague-Dawley rats had developed a bradycardia at exercise on submaximal work loads. This bradycardia was also present after autonomic denervation and in isolated perfused heart preparations. The heart weight/body weight ratio was increased in these trained animals compared to untrained littermates. Sympathectomized, trained rats developed the same degree of cardiac hypertrophy, but their heart rate after denervation and in the isolated heart was the same as in Sympathectomized, untrained rats.
It is concluded that the bradycardia of trained and thereafter denervated animals seen in this and a previous investigation represents an adaptation within the heart itself, since it was present in the isolated heart. These results thus provide further evidence for a non-neural component in training-induced bradycardia. Since the trained Sympathectomized rats had a cardiac hypertrophy but no reduction of intrinsic heart rate, it seems likely that the myocardial mass is of minor importance for the level of intrinsic heart rate.
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Arcos JC, Sohal RS, Sun S-C, Argus MF, Burch GE (1968) Changes in ultrastructure and respiratory control in mitochondria of rat heart hypertrophied by exercise. Exp Mol Pathol 8: 49–65
åstrand P-O, Rodahl K (1977) Textbook of work physiology. McGraw-Hill, New York, pp 423–433
Bolter CP, Hughson RL, Critz JB (1973) Intrinsic rate and cholinergic sensitivity of isolated atria from trained and sedentary rats. Proc Soc Exp Biol Med 144: 364–367
Conolly ME, Kersting F, Dollery CT (1976) The clinical pharmacology of beta-adrenoceptor-blocking drugs. Prog Cardiovasc Dis 19: 203–234
Crews J, Aldinger EE (1967) Effect of chronic exercise on myocardial function. Am Heart J 74: 536–542
De Champlain J, van Ameringen MR (1972) Regulation of blood pressure by sympathetic nerve fibres and adrenal medulla in normotensive and hypertensive rats. Circ Res 31: 617–628
Ekblom B, Kilbom å, Malmfors T, Sigvardsson K, Svanfeldt E (1973) Sympathectomy and pharmacological blockade in trained rats. Acta Physiol Scand 89: 283–285
von Euler US (1956) Noradrenaline. Chemistry, physiology, pharmacology and clinical aspects. CC Thomas Publ, Springfield Il, pp 109–116
Finch L, Leach GDH (1970) A comparison of the effects of 6-hydroxydopamine immunosympathectomy and reserpine on the cardiovascular reactivity in the rat. J Pharm Pharmacol 22: 354–360
Frick MH, Elovainio RO, Somer T (1967) The mechanism of bradycardia evoked by physical training. Cardiologia 51: 46–54
Gauthier P, Nadeau R, De Camplain J (1972) Acute and chronic cardiovascular effects of 6-hydroxydopamine in dogs. Circ Res 31: 207–217
Gerola A, Feinberg H, Katz LN (1957) Oxygen cost of cardiac hemodynamic activity. Physiologist 1: 31
Harri MNE, Narvola I (1979) Physical training under the influence of beta blockade in rats: Effect on adrenergic responses. Eur J Appl Physiol 41: 199–210
Heroux O, Gridgeman NT (1958) The effect of cold acclimation on the size of organs and tissues of the rat, with special reference to modes of expression of results. Can J Biochem Physiol 36: 209–216
Hughson RL, Sutton JR, Fitzgerald JD, Jones NL (1977) Reduction of intrinsic sinoatrial frequency and norepinephrine response of the exercised rat. Can J Physiol Pharmacol 55: 813–820
Jaweed MM, Herbison GJ, Ditunno JF, Gordon EE (1974) Heart weight of rat in different exercises. Arch Phys Med Rehabil 55: 539–544
Jose AD (1966) Effect of combined sympathetic and parasympathetic blockade on heart rate and cardiac function in man. Am J Cardiol 18: 476–478
Krakoff LR, Ginsburg SM (1973) Effect of chemical sympathectomy on pressor responses to norepinephrine, angiotensin and tyramine. Experientia 29: 995–997
Lewis SF, Nylander E, Gad P, Areskog N-H (1980) Non-autonomic component in bradycardia of endurance trained men at rest and during exercise. Acta Physiol Scand 109: 297–305
Malmfors T, Thoenen H (eds) (1971) 6-hydroxydopamine and catecholamine neurons. North Holland Publ Co, Amsterdam London New York, pp 15–74
Mueller RA, Thoenen H, Axelrod J (1969) Adrenal tyrosine hydroxylase: compensatory increase in activity after chemical sympathectomy. Science 163: 468–469
Nylander E (1981a) Effect of beta adrenergic receptor blockade on development of training-induced bradycardia in rats. Acta Physiol Scand (in press)
Nylander E (1981b) Intrinsic heart rate. Investigations in training-induced bradycardia in rats and humans. Linköping University Medical Dissertations, no 114, p 24–28
Oscai LB, Molé PA, Brei B, Holloszy JO (1971a) Cardiac growth and respiratory enzyme levels in male rats subjected to a running program. Am J Physiol 220: 1238–1241
Oscai LB, Molé PA, Holloszy JO (1971b) Effect of exercise on cardiac weight and mitochondria in male and female rats. Am J Physiol 220: 1944–1948
östman-Smith I (1976) Prevention of exercise induced cardiac hypertrophy in rats by chemical sympathectomy (guanethidine treatment). Neuroscience 1: 497–507
östman-Smith I (1979) Adaptive changes in the sympathetic nervous system and some effector organs of the rat following long term exercise or cold acclimation and the role of cardiac sympathetic nerves in the genesis of compensatory cardiac hypertrophy. Acta Physiol Scand [Suppl] 477: 41–52
Robinson BF (1967) Relation of heart rate and systolic blood pressure to the onset of pain in angina pectoris. Circulation 35: 1073–1083
Shipley RE, Tilden JH (1947) A pithed rat preparation suitable for assaying pressor substances. Proc Soc Exp Biol Med 64: 453–455
Sigvardsson K, Svanfeldt E, Kilbom å (1977) Role of the adrenergic nervous system in development of training-induced bradycardia. Acta Physiol Scand 101: 481–488
Smith DC, Ei-Hage A (1978) Effect of exercise training on the chronotropic response of isolated rat atria to atropine. Experientia 34: 1027–1028
Sutton JR, Cole A, Gunning J, Hickie JB, Seldon WA (1967) Control of heart rate in healthy young men. Lancet 1: 1398–1400
Tipton CM, Matthes RD, Tcheng T-K, Dowell RT, Vailas AC (1977) The use of the Langendorff preparation to study the bradycardia of training. Med Sci Sports 9: 220–230
Van Liere EJ, Northup DW (1957) Cardiac hypertrophy produced by exercise in albino and hooded rats. J Appl Physiol 11: 91–92
Wennmalm å (1979) Prostacyclin-dependent coronary vasodilatation in rabbit and guinea pig hearts. Acta Physiol Scand 106: 47–52
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Nylander, E., Sigvardsson, K. & Kilbom, å. Training-induced bradycardia and intrinsic heart rate in rats. Europ. J. Appl. Physiol. 48, 189–199 (1982). https://doi.org/10.1007/BF00422980
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DOI: https://doi.org/10.1007/BF00422980