Negative chronotropic effects of thyroxine on the isolated bullfrog heart.
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.
D000818:Animals; D016275:Atrial Function; D002104:Cadmium / Q000494:pharmacology; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D011892:Rana catesbeiana; D012966:Sodium Cyanide / Q000494:pharmacology; D013974:Thyroxine / Q000494:pharmacology*
D002104:Cadmium; D012966:Sodium Cyanide; D013974:Thyroxine