Thermoregulatory effects of (D-ala2)-methionine-enkephalinamide in the cat. Evidence for multiple naloxone-sensitive opioid receptors.

(D-ala2)-methionine-enkephalinamide (DAME) was injected into the third cerebral ventricle of unrestrained cats. At ambient temperature (Ta) = 22 degrees C, 3.1-50 micrograms caused dose-related hyperthermias. As dosage was increased, the hyperthermias diminished and in some cats hypothermia developed. Hyperthermia was not due to pyrogenic contamination or prostaglandin synthesis since it was not altered by pretreatment with a large IV dose of indomethacin. However, pretreatment with naloxone did cause a dose-related reduction in the hyperthermia. A low dose of DAME (12.5 micrograms) also caused hyperthermia at Ta = 4 and 32 degrees C, indicative of an increase in the level about which body temperature was regulated. On the other hand, a dose of 200 micrograms, which caused hyperthermia Ta = 22 and 32 degrees C, usually caused hypothermia at Ta = 4 degrees C, perhaps due to impairment of thermoregulatory control mechanisms. The response to DAME in the cold was reduced by naloxone pretreatment or reversed by subsequent injection of naloxone. Differences in hyperthermic patterns over a range of TaS and the lack of hypothermogenic action of morphine indicate that DAME alters thermoregulation in the cat by acting on morphine-insensitive, but naloxone-sensitive receptors. Central injection of beta-endorphin (5-50 micrograms) caused a dose-related hyperthermia. (Des-tyr1)-leucine-enkephalin (10-250 micrograms) was weakly hyperthermogenic, and kyotorphin (500 micrograms) did not consistently alter body temperature.