Reactivity of rat abdominal aorta to U46619 following whole-body gamma irradiation.

Rats exposed to 20 Gy whole-body irradiation demonstrated a depressed aortic responsiveness to the thromboxane mimic, U46619, 48 h postirradiation. The mechanism for this observed response was investigated. Shielding the abdominal aorta attenuated this altered vascular reactivity. Since this suggests that radiation exposure induces local changes in the aorta, vascular smooth muscle function was assessed with cumulative concentrations of KCl. Radiation-induced smooth muscle damage was insufficient to account for the decreased reactivity to U46619. Next, calcium availability for vascular smooth muscle function was evaluated and found not to be responsible for the radiation-induced depression in aortic responsiveness. Finally, the role that cyclooxygenase products play in the depressed contractile response was investigated. Indomethacin treatment prior to and for 48 h after irradiation attenuated the altered vascular reactivity to U46619. These data suggest that a radiation-induced increase in cyclooxygenase products may play a role in the decreased aortic reactivity to the thromboxane mimic.