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  • 1980-1984  (3)
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  • 1
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effects of chronic thyroxine treatment on cat soleus muscle contractions were studied.2. Maximum twitch tension, contraction time, half relaxation time and tensiontime integral of maximal twitches of the soleus muscles of thyroxine treated cats were significantly decreased. Consequently, there was a decrease in tension and degree of fusion of incomplete tetanic contractions of the soleus muscle. The maximum tetanic tension was not statistically significantly changed, suggesting that the effects may be due to a decrease in the duration of the active state of the muscle.3. Isoprenaline given intravenously during incomplete tetanic contractions of the soleus muscle caused a statistically significant depression of tension in the control group but not in the thyroxine treated group. This further suggests reduction in the duration of the active state of soleus muscles of thyroxine treated cats.4. Propranolol injected chronically with thyroxine reversed or prevented the depression of tension caused by thyroxine treatment, suggesting the involvement of β-adrenoceptors in these effects.5. The decrease in tension and degree of fusion during incomplete tetanic contractions of the thyroxine treated soleus could be responsible, at least partly, for the muscle weakness and tremor of thyrotoxicosis. Cyclic AMP may possibly be the mediator of these effects.
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  • 2
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Cyclic AMP levels have been determined in the soleus muscles of anaesthetized cats in the absence of drugs, and during depression of incomplete tetanic contractions produced by (-)-isoprenaline, ICI 63,197 (a phosphodiesterase inhibitor) or levodopa.2. Cyclic AMP levels were elevated at the peak of tension depression produced by isoprenaline. Effects of isoprenaline on cyclic AMP and on contractions were dose dependent and statistically significantly related one to the other. Both effects were blocked by propranolol.3. ICI 63,197 and levodopa produced isoprenaline-like effects on contractions but times to peak effect and recovery were longer. Cyclic AMP levels estimated during the depressant action were elevated.4. The results support the involvement of cyclic AMP in the depressant effect of β-adrenoreceptor agonists on slow-contracting mammalian skeletal muscle.
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  • 3
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Cyclic AMP and cyclic GMP levels were determined in bovine splenic nerve segments in the absence and presence of (±) - isoprenaline, (-)-phenylephrine, clonidine and ICI 63 197 (a phosphodiesterase inhibitor). The chosen concentrations of adrenoceptor agonists were those which are known to affect stimulation-induced overflow of noradrenaline from nerve terminals.2. The mean levels of cyclic AMP ranged from 229 to 555 pmol/g of microwave irradiated tissue. Mean cyclic GMP levels ranged from 27.9 to 42.2 pmol/g.3.Isoprenaline enhanced cyclic AMP levels but did not affect cyclic GMP levels. The effect was blocked with (±)-propranolol. ICI 63 197 increased cyclic AMP levels but did not change cyclic GMP. Phenylephrine and clonidine caused no consistent changes in cyclic AMP or cyclic GMP levels or in the concentration ratio between these two nucleotides.4.The results support the involvement of cyclic AMP in the enhancing effect of β-adrenoceptor agonists and phosphodiesterase inhibitors on stimulation-induced release of noradrenaline from sympathetic nerves.
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