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Effects of X-ray irradiation on the hearing with CM and ABR to both air- and bone-conduction stimuli were studied continuously from immediately after the irradiation to a few weeks later. At 2, 4, and 6 krad, only slight conductive hearing impairment was found, but at 8 krad or more, CM and ABR disappeared abruptly, after having increased briefly. Advanced sensorineural hearing loss appeared at about 10 hours after irradiation ended at 8 krad, at about 6 hours at 10 krad, and at about 3 hours at 12 krad. More severe hearing impairment was observed at higher frequencies and the endocochlear d.c. potential (EP) decreased at about 7 hours after 10 krad irradiation. Histologically, no discernible changes in the hair cells or sensory hairs were found with a scanning electron microscope at about 6 hours after 10 krad irradiation, while with a transmission electron microscope, the outer hair cells in the basal coil of the cochlea were found to be mostly destroyed. However, no changes could be found in the inner hair cells or other supporting cells.

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By using the ESR spin trapping technique with the N-methyl-D-glucamine dithiocarbamate (MGD)2-Fe(II) complex, the generation of nitric oxide (NO), a gaseous free radical, was observed in NO spin trapping solution bubbled with the filtered main-stream of cigarette smoke. The ESR signal with a three-line spectrum characteristic of an NO radical, which was not observed immediately after bubbling of smoke, started rapidly increasing with time up to around 25 min after the last addition of ferrous ions Fe(II), and then slowly approached a peak value dependent on the burned cigarette mass and on the smoking speed. The production of NO was, however, much affected by air oxidation and enhanced by the addition of ascorbic acid. A certain concentration of sodium nitrite (NaNO2) solution, in which nitrite NO2- is assumed as the main origin of the NO, mimicked closely the time course of NO generation resulting from the smoke of one cigarette. The cigarette smoke that was passed through alkaline pyrogallol solution as a deoxidizer; however, it exhibited an unchanged intensity of NO signal throughout the measurement. These results strongly suggest that NO would be gradually reproduced from NO2- in the reductive aqueous solution containing excess Fe(II) through NO2, which is initially formed and is concomitantly oxidized from NO in cigarette smoke.