 This further indicates (see previous section) that the balance between the TXA2-TP and PGI2-IP axes contribute to regulating platelet function, blood clotting, and bleeding.Animal model studies indicate that TP receptor activation contracts vascular smooth muscle cells and acts on cardiac tissues to increase heart rate, trigger Cardiac arrhythmias, and produce myocardial ischemia.These effects may underlie, at least in part, the protective effects of TP gene knockout in mice.