Influence of endothelin 1 receptor inhibition on functional, structural and molecular changes in the rat heart after irradiation.

Radiation-induced heart disease is a severe side effect of thoracic radiotherapy. Studies suggest that mast cells play a protective role in radiation-induced heart disease and that the endothelin (ET) system mediates protective effects of mast cells in other disorders. This study examined whether mast cells modulate the cardiac ET system and examined the effects of ET receptor inhibition in a rat model of radiation-induced heart disease. Mast cell-deficient (Ws/Ws), mast cell-competent (+/+) and Sprague-Dawley rats received 18 Gy irradiation to the heart. Left ventricular mRNA of ET1 and its receptors (ETA and ETB) was measured in Ws/Ws and +/+ rats at 1 week and 3 months. Sprague-Dawley rats were treated with the ETA/ETB antagonist bosentan, and at 6 months cardiac changes were assessed using the Langendorff perfused rat heart preparation, immunohistochemistry and real-time PCR. Ws/Ws and +/+ rat hearts did not differ in baseline mRNA. In contrast, +/+ rats hearts exhibited up-regulation of ET1 after irradiation, whereas Ws/Ws rats hearts did not, suggesting the possibility of interactions between mast cells and the cardiac ET system. Bosentan induced reductions in left ventricular systolic pressure, developed pressure and +dP/dtmax but did not affect fibrosis. Because of the known opposing effects of ETA and ETB, studies with selective antagonists may clarify the role of each receptor.