Cyclazocine and norepinephrine uptake, metabolism, and turnover in the rat brain

The effects of cyclazocine, a narcotic agonist/antagonist, on the uptake, metabolism, and turnover of norepinephrine in rat brains were studied. Cyclazocine significantly depressed the accumulation of intracisternally administered [3H]norepinephrine and the formation of 3,4-[3H]dihydroxymandelic acid but did not alter the formation of [3H]-normetanephrine. Comparatively, imipramine reduced the uptake of [3H]norepinephrine, decreased the formation of 3,4-[3H]dihydroxymandelic acid, and increased the formation of [3H]normetanephrine. Moreover, cyclazocine increased the formation of endogenous 3-methoxy-4-hydroxyphenylethylene glycol and produced a fall in endogenous norepinephrine. It is suggested that cyclazocine reduces the accumulation of [3H]norepinephrine, decreases endogenous norepinephrine levels, and increases the formation of 3-methoxy-4-hydroxyphenylethylene glycol by interacting with brain adrenergic nerves, presumably by inhibiting neuronal uptake and facilitating norepinephrine turnover.