Myo-inositol turnover in the intact rat brain: increased production after d-amphetamine.

Apparent turnover of myo-inositol in the brain of urethane-anesthetized rats was estimated in vivo from the rate of appearance of endogenous myo-inositol in the cerebroventricular compartment. Ventricular-cisternal perfusion technique combined with isotope dilution of [14C]myo-inositol was used to determine the rate of appearance of brain-produced myo-inositol and its modification by d-amphetamine. A mean value of 0.75 nmol/min was obtained for the rate of appearance in the cerebroventricular system. A dose-dependent increase in this rate was seen after the administration of d-amphetamine. The endogenous removal of myo-inositol from the perfusate was also studied and found to be mediated in part by a saturable transport system that was not influenced by d-amphetamine. The rate of entry of myo-inositol from blood to the cerebroventricular system was very low and accounted for only 2% of the total rate of appearance, indicating that the majority of myo-inositol in the rat cerebroventricular fluid originates in the brain.