Free radicals in surviving tissues

The leaves of plants and germinating seeds contain unpaired electrons, or free radicals, which can be detected from their interaction with a magnetic field in an electron spin resonance (ESR) spectrometer. The ESR spectrometer applies an external magnetic field to the sample, and the "ESR signal" is a measurement of the absorption of microwave energy by these unpaired electrons, as the magnetic field is varied. In 1961, Commoner and Ternberg used the ESR technique to detect free radicals in mammalian tissues.

The ESR signal from the surviving tissue of the body remains for up to 100 minutes after death. In the research described below, rats, mice, and guinea pigs were sacrificed, and the surviving tissue was quickly removed and placed into an ESR spectrometer. The signals obtained from surviving samples of guinea pig tissue are shown (below). Liver, intestine, and kidneys had the largest amount of free radicals, whereas skeletal muscle had an undetectable ESR signal.

From ESR free radical signals

Liver tissue from guinea pig, rat, and mouse had a high ESR signal, as shown in the bar graphs (below).

From ESR free radical signals

The authors reasoned that the ESR signal observed in mammalian tissues might be due to the enzymatic redox activity of mitochondria. Liver and kidney organs are relatively rich in mitochondria, and gave the most robust ESR signal, whereas skeletal muscle has almost no signal and is known to contain relatively few mitochondria.


Reference

COMMONER B. and J. L. TERNBERG. (1961). Free radicals in surviving tissues. Proc. Natl. Acad. Sci. U. S. A. 47, 1374-1384. DOI:10.1073/pnas.47.9.1374