Monitoring guinea pig core temperature by telemetry during inhalation exposures

A temperature telemetry system was incorporated into an existing animal model for inhalation toxicology. This system facilitated continuous monitoring of guinea pig temperature during inhalation exposures. Components of the system included Mini-Mitter temperature-controlled oscillators, AM receivers, and an IBM microcomputer. Software was developed to perform signal processing and filtering. Transmitters were calibrated and then sterilized and surgically implanted in the guinea pig peritoneum. Monitoring the baseline temperature of nine animals indicated a mean temperature of 38.6 +/- 0.3 degrees C. Guinea pigs were treated with agents to induce transient hypo- or hyperthermia. For the former, exposure for 3 hr to 7.8 ppm diphenylmethane-4,4'-diisocyanate resulted in a 3 degrees C temperature decrease. The temperature was determined from 230 readings per animal per hour. Inhalation of 9 or 44 micrograms/m3 endotoxin for 6 hr induced hyperthermia with a 1.5 degrees C maximum increase in core temperature at 4.8 hr. With endotoxin, an increase in respiratory rate was also noted and followed the same pattern as temperature with a maximal increase of 52% occurring at 4.2 hr. The temperature telemetry system enabled continuous long-term monitoring of toxicant-induced hypothermia and pyrexia without interruption of inhalation exposure or measurements of respiratory parameters.