Myocardial catecholamine responsiveness of spontaneously hypertensive rats as influenced by swimming training
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Alterations of myocardial mechanical catecholamine responsiveness by swimming training (2×90 min/day, 4 weeks) were examined in 13-week-old spontaneously hypertensive male rats (SHR). The relationships between myocardial mechanical catecholamine responsiveness and ventricular β-adrenoceptors as well as myosin isoenzyme pattern were also examined. Compared with sedentary controls, trained rats showed a greater responsiveness to isoproterenol (10−6 mol/l) on isometric tension (T) and its first derivative (dT/dt) (ΔT:0.45±0.55 vs. −0.15±0.11 10−2 N/mm2, p<0.01, ΔdT/dt: 17.1±10.1 vs. 8.3±3.6 10−2 N/mm2·s, p<0.05). In sedentary SHR, dT/dtmax increased significantly, whereas developed tension decreased slightly, coupled with a decrease of time to peak tension by high dose (10−6 mol/l) isoproterenol. Therefore, it can be stated that dT/dt is a better indicator for catecholamine sensitivity than isometric tension. β-adrenoceptor density ([3H]-dihydroalprenolol binding) decreased significantly in trained rats (68.7±7.62 vs. 102.4±4.37 fmol/mg protein, p<0.01) with no significant difference in KD values (4.61±2.26 vs. 6.11±1.94 nM, ns). In addition, myosin isoenzyme pattern revealed by pyrophosphate gel electrophoresis shifted towards VM-1 after swimming training. The increased catecholamine sensitivity of fast contracting myocardium is, in principle, compatible with the assumption of cAMP-dependent regulation of myofibrillar ATPase activity (21) or cross bridge kinetics (9), although other postreceptor processes should also be taken into consideration for the increased catecholamine sensitivity.
Key wordscatecholamine responsiveness training spontaneously hypertensive rat isometric tension β-adrenoceptor myosin isoenzymes
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- 2.Ayobe MH, Tarazi RC (1983) Beta-receptors and contractile reserve in left ventricular hypertrophy. Hypertension 5 (suppl I):192–197Google Scholar
- 4.Cervoni P, Herzlinger H, Lai FM, Tanikella T (1981) A comparison of cardiac reactivity and β-adrenoceptor number and affinity between aorta-coarcted hypertensive and normotensive rats. Br J Pharmac 74:517–523Google Scholar
- 10.Jacob R, Kissling G, Ebrecht G, Holubarsch C, Medugorac I, Rupp H (1983) Adaptive and pathological alterations in experimental cardiac hypertrophy. In: Chazov E, Saks V, Rona G (eds) Advances in Myocardiology, Vol 4, pp 55–77. Plenum Publishing Corporation, New YorkGoogle Scholar
- 13.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 477:1–118PubMedGoogle Scholar
- 16.Rupp H, Bukhari AR, Jacob R (1983) Modulation of catecholamine synthesizing and degrading enzymes by swimming and emotional excitation in the rat. In: Jacob R, Gülch RW, Kissling G (eds) Cardiac adaptation to hemodynamic overload, training and stress, pp 267–273. Dr D Steinkopff Verlag. DarmstadtGoogle Scholar
- 17.Scatchard G (1949) The attractions of proteins for small molecules and ions. Ann NY Acad Sci 51:660–672Google Scholar