Ultra-low dose beta-irradiation induces constriction of rabbit carotid arteries via the endothelium

PURPOSE: To investigate the action of ultra-low dose beta-radiation (ULDBR) on isolated segments of blood vessels. MATERIALS AND METHODS: We used the pharmacological model of isolated rabbit carotid arteries with intact or mechanically removed endothelium. Specific vascular responses to beta-irradiation were registered after addition of (90)Sr in the concentration range between 12 and 96 microCi l(-1) to the organ bath containing physiological salt solution (PSS). RESULTS: Intact vascular rings, preconstricted with 20 mM K(+)-PSS, developed an additional constriction upon the addition of (90)Sr depending on the absorbed radiation dose (21.5, 42.9, 85.8, and 171.6 microGy) and the dose rate (51.5, 103.0, 206.0 and 412.0 microGy h(-1)). The vasoconstriction due to (90)Sr was absent in the endothelium-denuded vascular segments indicating the endothelium dependent action of ULDBR. Irradiation did not alter the endothelium dependent relaxation of rabbit carotid arteries induced by acetylcholine. The endothelium dependent responses to ULDBR were abolished after increasing the extra-cellular K(+) to 40 mM. CONCLUSIONS: ULDBR acts on rabbit carotid arteries as a pharmacological signalling agent because ULDBR effects were completely reversible. ULDBR-mediated contractile responses of the vessels are endothelium dependent. The resistance of acetylcholine endothelium-dependent relaxation of rabbit carotid arteries to ULDBR indicates that the polyphosphoinositide-nitric oxide (NO) signalling cascade is not impaired by ULDBR in endothelial cells.