Influence of thyroid hormone on the positive inotropic effects mediated by α- and β-adrenoceptors in isolated guinea pig atria and rabbit papillary muscles
There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
Effects of thyroxine treatment for 7--11 days on the positive inotropic effects mediated
by alpha- and beta-adrenoceptors were studied in isolated guinea pig atria and rabbit
papillary muscles. In guinea pig atria, the thyroxine treatment inhibited the positive
inotropic effect of lower concentrations of phenylephrine (PHE), and attenuated the
inhibitory effect of phentolamine on the PHE response. The effect of isoproterenol
(ISO) was potentiated by the thyroxine treatment. In rabbit papillary muscles, the
thyroxine treatment shifted the dose--response curve for PHE to the right and attenuated
the inhibitory effect of phentolamine on the PHE response. Propranolol, in both guinea
pig atria and rabbit papillary muscles, inhibited the PHE response more effectively
in preparations from thyroxine-treated animals than in controls. In guinea peg atria,
the attenuation of the PHE response mediated by alpha-adrenoceptors was observed after
the thyroxine treatment for only 2 days, whereas the potentiation of the ISO response
required the thyroxine treatment for a longer period. It was concluded that the thyroxine
treatment attenuated the positive inotropic effect mediated by alpha-adrenoceptors
and potentiated that mediated by beta-adrenoceptor-mediated positive inotropic effects
due to the thyroxine treatment may be independent of each other.