Abstract
Summary
Thirteen, male and female sheep were electrically anesthesized (using a variable voltage-frequency, bitemporal electrode technique) during whole body exposure to 1 of 3 ambient temperature ranges, —10 to 5°C (“cold stressing”), 18 to 23°C (“thermoneutral”) and 27 to 29°C (“heat stressing”). Thermoregulatory mechanisms were examined at each temperature range, without drug treatment, during mild tranquilization (1.1 mg Propiopromazine HCl, i.v.), during 2 hours of electro-anesthesia and for a subsequent 3-hour recovery period. Except during “cold stressing” exposures, rectal temperature rose as hyperthermic polypneic reflexes were inhibited (15 breaths/°C change in rectal temperature) during electro-anesthesia but near-normal respiratory responses were reinstated after transcranial current flow ceased (120 breaths/°C change in rectal temperature) with rectal temperature returning to a normal range. Internal temperatures did not increase with electro-anesthesia during “cold stress.” A concept is proposed wherein it is suggested that the effect of electro-anesthesia is to inhibit partially normal thermoregulatory reflexes, resulting in transient heterothermia (similar to but more profound than chemical tranquilizer effects) with an additional shifting of a “thermoneutral zone” to a lower environmental temperature range due to increased somatic muscle tone.