Abstract
Summary
Beat rate determinations were made of the hearts of euthyroid, thyroxinized and triiodothyroninized rats in vivo and of atrial preparations of correspondingly treated (except for thyroxine) animals in vitro. A close parallelism was found between in vivo and in vitro experiments. Durations of the effects of thyroxine and triiodothyronine were equal. In radiothyroidectomized animals the rate of beat in isolated atria was less than 60% of that of euthyroid atria although no significant differences were observed in the heart rates of intact hypo- and euthyroid animals.
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