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  • 1
    Electronic Resource
    Electronic Resource
    Myocardial catecholamine responsiveness of spontaneously hypertensive rats as influenced by swimming training (1985)
    Springer
    Basic research in cardiology 80 (1985), S. 384-391 
    Details
    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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  • 2
    Electronic Resource
    Electronic Resource
    Association of ventricular myosin heavy chains in functional states which lead to isoenzyme populations encompassing the whole range of possible distribution (1985)
    Springer
    Basic research in cardiology 80 (1985), S. 608-616 
    Details
    ISSN: 1435-1803
    Keywords: exercise ; fasting ; isoenzymes ; myosin ; SHR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A statistical model is presented which describes quantitatively the distribution of ventricular myosin (VM) isoenzymes VM-1, VM-2 and VM-3. In order to account for the actual distribution of the isoenzymes, it was assumed that the probability for formation of the heterodimer VM-2 (alpha- and beta-heavy chain) is lower than that of the homodimers VM-1 (2 alpha-heavy chains) or VM-3 (2 beta-heavy chains). The relation VM-2=0.85 (VM-1·VM-3)0.5 describes quantitatively the proportion of the 3 isoenzymes in a given population. The model was established for 252 sedentary normotensive Wistar rats and spontaneously hypertensive rats (SHR) fed ad libitum. It is demonstrated that the isoenzyme populations of rats subjected to 8 weeks experimental routines involving intermittent feeding (1 day feeding ad libitum, followed by 1 or 2 days fasting) or swimming also obey this theoretical distribution. Intermittent feeding led to an increased proportion of VM-3 in Wistar rats and SHR, whereby the latter approached the limits of the possible distribution. Intermittent swimming resulted in an increased proportion of VM-1 which was independent of the feeding schedule in SHR. In Wistar rats, however, the swimming rats fed intermittently exhibited a significantly smaller proportion of VM-1. By combining certain experimental routines, it is thus possible to induce within 8 weeks an isoenzyme population of a predefined composition, nearly within the whole range of possible distribution. The data further demonstrate that the formal correlation between the proportion of beta-heavy chains in a myosin population and ventricular mass holds only when the rats are kept under standard conditions. Following the routines involving an altered pattern of food intake or intense physical activity, the isoenzyme population can be altered in a manner unrelated to ventricular mass. Thus, swimming induced a redistribution in favour of VM-1 irrespective of the feeding pattern, although ventricular mass differed greatly in both the intermittently or ad libitum fed swimming rats. It is concluded that, besides ventricular mass, neuro-endocrine status is decisive for the isoenzyme population of myosin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01907859
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The influence of endurance training on mechanical catecholamine responsiveness, β-adrenoceptor density and myosin isoenzyme pattern of rat ventricular myocardium (1985)
    Springer
    Basic research in cardiology 80 (1985), S. 88-99 
    Details
    ISSN: 1435-1803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An investigation was carried out on the effects of 4 weeks' swimming training (2×90 min/day) on myocardial isometric tension development and rate of tension rise, and also on the changes induced therein by in vitro application of isoproterenol. This was done in 9 isolated papillary muscles of 9-weekold male Wistar rats and the results were compared with the data of age-matched sedentary controls. Ventricular β-adrenoceptors ([3H]-dihydroalprenolol binding) and the isoenzyme pattern of myosin (pyrophosphate gel electrophoresis) were examined in the same individuals. Isometric tension (T) and its first derivative (dT/dt) measured at the optimum of the length-tension diagram were moderately increased by long-term swimming training. Isoproterenol (10−5 mol/l) induced a greater absolute and relative increase of both mechanical parameters in specimens of trained animals than in age-matched controls (†T: 3.6±1.6 vs. 1.9±0.6×10−2 N/mm2, p〈0.05. †dT/dt: 43.4±14.0 vs. 30.4±9.5×10−2 N/mm2·s, p〈0.05). K d decreased significantly (4.23±1.0 vs. 2.44±0.3 nM, p〈0.02), indicating an increase in receptor affinity, whereas receptor density revealed a tendency to decrease (98.8±22.6 vs. 67.1±18.0 fmol/mg protein, p〈0.1). In addition, there was a shift in the isoenzyme pattern of myosin towards VM-1 after swimming training. Thus, under the conditions of the present experiments, the mechanical response to isoproterenol does not correlate to β-adrenoceptor density. It is probable that, apart from the altered sensitivity of the receptors, other membrane or post-membrane processes, are responsible for the increased mechanical responsiveness to catecholamines. Although a relationship between myosin isoenzyme pattern and mechanical responsiveness to catecholamines is apparent taking into account our results and the findings on hypertensive rats as reported in the literature, it cannot be accounted for simply by altered β-adrenoceptor density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01906747
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    Paper (German National Licenses)
    Fulltext
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