Mechanogram Observations on the Isolated Auricle of Hypothyroid Rat

Abstract

Summary. The mechanogram of isolated spontaneously beating auricle of hypothyroid (treated with I 131 ), normal and thyroxinized rats was recorded at 4° C intervals over a temperature range of 25° to 41° C. The rate of beat in various preparations showed no qualitative differences as a function of temperature. The ability of heart muscle to increase the contraction force with falling temperature seems to presuppose the presence of thyroid action. Therefore the mechanical output of hypothyroid auricles was powerfully depressed by lowering the temperature. The weaker the thyroid activity, the longer the duration of the contraction period at a certain temperature. As a function of rate, the duration of contraction was independent of thyroid action.