Oxidation-reduction potentials in the cecal contents of rats and mice.

The oxidation-reduction potential (ORP) in the cecal contents of conventional rats, germ-free mice, and mice with a Colonization Resistance Factor flora (CRF-mice) was investigated. By using animals that were anaesthetized for a longer period of time, we attempted to eliminate the disturbing influence of oxygen. In addition, measurements were made under anaerobic conditions. For the rats, the ORP values reached a more or less constant level after about 30 min following the insertion of the electrodes. The mean ORP at that time was -458 mV (SD = 45 mV). The mean ORP values for the mice showed a more gradual reduction than was found in the rats. The curves leveled off at about 100 min following the insertion of the electrodes. The mean ORP values 100 min after electrode insertion were: germ-free mice, + 3 mV (SD = 39 mV); CRF-mice, -554 mV (SD = 29 mV). In rats, the ORP value decreased after death; no decrease was observed in mice. No difference was found in the values obtained when measuring under anaerobic or aerobic conditions after death.