Glucose modulation of skin temperature responses during morphine withdrawal in the rat

Studies were undertaken to determine the effects of acute alterations in plasma glucose levels on the tail skin temperature (TST) response of morphine-dependent rats to naloxone-precipitated withdrawal. In morphine-dependent rats, treatment with dextrose at doses of 0.5 or 2.5 g/kg did not alter the normal 6.0 +/- 0.3 degrees C TST response to naloxone. However, treatment with 5, 10 or 20 g dextrose/kg, which increased plasma glucose to 250 mg/dl or greater, blocked the TST response during morphine withdrawal. In contrast, an IV injection of 2.5 IU insulin (Na-porcine)/kg, which reduced plasma glucose for 2 h, caused a delayed TST response of 4.7 +/- 0.4 degrees C in control rats and exaggerated the TST response normally observed in morphine-dependent rats treated with naloxone. Collectively, these data indicate that acute hyperglycemia can attenuate and hypoglycemia can enhance the skin vasodilation which accompanies precipitated morphine withdrawal. In view of our observation that naloxone-precipitated morphine withdrawal caused a marked increase in blood glucose, the sympathetic activation associated with opiate withdrawal may be intended to elevate blood glucose and thereby limit the manifestation of the withdrawal response.