The effect of thyroid dysfunction on the chronotropic response to noradrenaline.
Dose-response curves to noradrenaline in the presence and absence of beta-receptor antagonists were established with isolated atria from euthyroid, hypothyroid and hyperthyroid rats. Baseline atrial rate and Emax were significantly lower than normal in the hypothyroid group and significantly higher than normal in the hyperthyroid group. Differences between the groups were minimal for pD2 and range of response to noradrenaline. The response to beta-receptor antagonists was the same in all 3 groups with the exception of the hypothyroid group which showed an attenuated increase in baseline atrial rate with compounds possessing partial agonist activity. This was particularly marked for practolol. These results do not provide evidence for an altered responsiveness to catecholamines due to altered thyroid status but suggest that thyroid hormones have a direct action on cardiac tissue.
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D013959:Thyroid Diseases / Q000503:physiopathology*; D013974:Thyroxine / Q000097:blood
D000319:Adrenergic beta-Antagonists; D013974:Thyroxine; D009638:Norepinephrine