ISSN:
1435-1803
Keywords:
catecholamine responsiveness
;
training
;
spontaneously hypertensive rat
;
isometric tension
;
β-adrenoceptor
;
myosin isoenzymes
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01908182
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