IN-VIVO EPR STUDIES OF THE METABOLIC-FATE OF NITROSOBENZENE IN THE MOUSE

We report the first demonstration of EPR spectroscopy to study free ra dical reactions in live mice and excised muscle tissue resulting from the metabolism of nitrosobenzene. A broad three-line EPR spectrum (a(N ) = 11.6 G) appeared in the buttocks region of a mouse place in an L-b and loop gap resonator after intramuscular or intraperitoneal injectio n of 0.2 mmol/kg nitrosobenzene. The signal intensity reached a maximu m at 20 to 30 min and remained constant well beyond 2 h. If muscle tis sue was dosed with nitrosobenzene and excised within 5 min, a similar three-line X-band EPR spectrum was obtained which was preceded by the rapid growth and subsequent decay of an EPR spectrum identical with th at of the phenylhydronitroxide radical, which was presumably generated from reactions between nitrosobenzene and reducing agents in the bloo d or tissue such as NADH or ascorbic acid. A model system containing n itrosobenzene and unsaturated fatty acids (olive oil or animal fat) yi elded an identical three-line spectrum resulting from radical adducts of nitrosobenzone across the double bond. Overall, these results sugge st that the most probable mechanism in vivo was nitrosobenzene covalen tly adding (''binding'') to polyunsaturated fatty acid clusters in fat or membranes.