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Negative chronotropic effects of thyroxine on the isolated bullfrog heart
Abstract:
An acute application of L-thyroxine (T4) to everted sinus-atrium preparations of bullfrog showed negative chronotropic effects consisting of two processes: an initial peak at 2-5 min and a delayed plateau at 40-60 min. The initial effect was blocked by Cd2+ and tetraethyl-ammonium (TEA). The delayed effect was suppressed by Cd2+ and NaCN.