The effects of a lethal gamma irradiation were investigated on cerebral NO-ergic system by using a voltammetric method in freely moving rats. It is reported that the cortical NO concentration increases right from the end of the radiation exposure (15 Gy) and reaches a maximal magnitude (+120%) 24 h later. A dose-effect relationship from 2 to 15 Gy for gamma-ray exposure has also been observed. The effects, obtained with either an NO synthase inhibitor nonselective for the different NO synthase isoforms or an NO synthase inhibitor selective for the constitutive isoform, suggest that the radiation-induced increase in NO is likely to be dependent on the inducible NO synthase isoform. Moreover, experiments performed under ex vivo conditions showed that the cortical mRNA level for Ca++-independent NO synthase, the brain NOS activity, and urinary nitrites/nitrates increased significantly 24 h after gamma-ray exposure. These results demonstrate that a supralethal wholebody irradiation alters the NO-ergic pathways. The increase in NO obtained under such conditions might constitute a good index of central nervous system radiosensitivity during the acute phase of the radiation syndrome. (C) 2003 by Radiation Research Society.

Purpose: To investigate the effect of blood nitric oxide (NO) as a mediator of the neurovascular syndrome in rats following gamma-irradiation.Material and methods: Using a voltametric method together. with a carbon fibre based sensor, NO measurements were carried out in sham-irradiated and irradiated animals either in blood from the: abdominal aorta or in blood samples from the heart.Results: In in vitro conditions, properties of the probe were not altered by the ionizing radiation. Significant increases of +17% and + 25.6% were observed in the voltametric signal height at 90 min and 24 h respectively after a 15 Gy gamma-ray exposure. These effects were followed on days 3 and 4 by a progressive decrease in the signal height of 7% and 18% respectively. Dose-effect relationships were observed at 90 min and 24-h after exposure to gamma-rays in the. range of 3-15 Gy. Finally, the NO dependence on the measured voltametric signal was controlled by using inhibitors of the NO synthase (NOS) and by performing nitrate assays.Conclusions: Specific blood NO voltametric measurements are possible. Functional changes associated with NO after gamma-ray exposure are discussed.