Effects of morphine and other centrally acting drugs on 3,4-dihydroxyphenylethylene glycol sulfate (DOPEG-SO4) in rat brain

Brain concentrations of DOPEG-SO4 were measured fluorometrically 0, 0.5, 1, 2, 4 and 8 hr after i.p. injections of morphine sulfate (20 mg/kg), d-amphetamine sulfate (5 mg/kg), desmethylimipramine HCl (25 mg/kg), or reserpine (5 mg/kg) in order to observe the effects of these drugs on intraneuronal norepinephrine degradation. No change in brain levels of DOPEG-SO4 was found until 8 hr after morphine, at which time the metabolite was significantly (p<.01) decreased. d-Amphetamine and desmethylimipramine significantly (p<.01) decreased the metabolite at all observed timepoints after 0 hr. Brain DOPEG-SO4 after reserpine was significantly (p<.01) increased at 0.5 and 1 hr, and significantly (p<.01) decreased at 4 and 8 hr. DOPEG-SO4 remained unchanged 0–8 hr after saline injections. These results, together with previous measurements of brain 3-methoxy-4-hydroxyphenylethylene glycol sulfate (MOPEG-SO4), indicate that the mechanism of morphine action on noradrenergic neurons differs from those of the other drugs examined and that morphine may cause central norepinephrine release.