The effect of ionizing irradiation on vasomotor reactivity in the rat thoracic aorta in vitro

Ionizing irradiation inhibits restenosis in animal models and human. Vasomotor tone preservation during and after radiation therapy is of clinical importance. We therefore investigated vascular reactivity following radiation therapy.

Wistar Sabra rats were treated with a single dose of 1000 cGy external X-ray irradiation. Vascular reactivity of 192 segments of rat thoracic aorta was studied in vitro in four groups (12 rats in each group, four segments from each aorta). Immediately after in vivo irradiation, immediately after ex vivo irradiation, 1 month after irradiation, and no irradiation (control).

Vasoconstriction to phenylephrine (PE) 10(-9)-10(-5) M or KCl 118.0 mM in all the irradiated groups was similar to controls. Endothelium-dependent vasorelaxation to acetylcholine (ACh) 10(-9)-10(-5) M in segments studied immediately after in vivo irradiation was increased compared to controls at all concentrations (109.7+/-35. and 90.0+/-40.0%, respectively, at 10(-5) M, P=.006). Endothelium-independent relaxation to nitroglycerin 10(-9)-10(-5) M in all irradiated groups was similar to controls.

External-ionizing irradiation with 1000 cGy in the rat aortic model induces acute and transient increase in endothelium-dependent relaxation to ACh, and does not alter vasoconstriction and endothelium-independent relaxation.