Effect of μ-, κ-, and δ-selective opioid agonists on thermoregulation in the rat

Abstract

The effect of selective μ-, κ-, and δ-agonists on brain surface temperature ( T b ), oxygen consumption ( V o 2 ), and heat exchange ( Q) was studied in unrestrained, male Sprague-Dawley rats using whole-body calorimetry. Hyperthermia, produced by PL-017 (1.86 nM) given ICV, resulted from increased V o 2 and reduced Q during the first 15–45 min postinjection. T b returned to control levels due to a combination of increased Q and reduced V o 2 . PL-017-induced hyperthermia was abolished by the μ-selective antagonist CTAP (0.75 nM). Dynorphin A 1–17 (4.65 nM), a κ-selective agonist, reduced both V o 2 and Q, resulting in hypothermia that was blocked by the κ-selective antagonist nor-binaltorphimine (25 nM). The δ-selective agonist DPDPE (4.64 nM) caused no significant changes in T b , V o 2 , or Q. The data indicate that central stimulation of the μ- and κ-opioid receptors affects both oxidative metabolism and heat exchange, which result in a change in T b . These alterations can be prevented with selective opioid antagonist pretreatment.