HYPOTHERMIC EFFECT OF D-ALA-DELTORPHIN-II, A SELECTIVE DELTA-OPIOID RECEPTOR AGONIST

The natural heptapeptide D-Ala-deltorphin II, the most selective agonist for delta-receptors currently available, was used to study the role of brain delta-opioid receptors in the control of body temperature. In rats placed in a cold ambient temperature (4-degrees-C), intracerebroventricular injections of D-Ala-deltorphin II produced a significant hypothermia. In animals at an ambient temperature of 22-degrees-C, only the highest dose employed induced a slight fall in body temperature. At a warm temperature (34-degrees-C), D-Ala-deltorphin II induced no significant changes in body temperature. D-Ala-deltorphin II-induced hypothermia, unaffected by naloxone, was significantly reduced by the selective delta-receptor antagonist naltrindole. These findings indicate that D-Ala-deltorphin II produces its hypothermic effects at a supraspinal delta-receptor, and support the involvement of delta-receptors in central control of body temperature.