The effects of acute and chronic morphine administration on the levels of 3-methoxy-4-hydroxphenylglycol sulfate in rat brain.
The acute and chronic effects of morphine on the turnover of norepinephrine (NE) were determined by measuring the changes in the levels of the sulfate conjugate of 3-methoxy-4-hydroxyphenylglycol (MHPG-SO4) in rat brain. Two hours after administration, morphine produced a dose-related increase in the levels of MHPG-SO4 suggesting an increase in NE turnover. The effect of morphine was evident by one hour after drug administration and was maintained for at least four hours but disappeared by eight hours. Chronic treatment with morphine resulted in lower baseline levels of MHPG-SO4 and the development of tolerance to its acute effect on NE turnover. These findings suggest that after chronic administration of morphine, the maintenance of a normal rate of norepinephrine turnover in brain is dependent upon the continued administration of maintenance doses of morphine.
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D004361:Drug Tolerance; D005470:Fluorometry; D006018:Glycols / Q000032:analysis / Q000378:metabolism*; D008297:Male; D008734:Methoxyhydroxyphenylglycol / Q000378:metabolism*; D009020:Morphine / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D013997:Time Factors
D006018:Glycols; D008734:Methoxyhydroxyphenylglycol; D009020:Morphine; D009638:Norepinephrine