Apparent turnover of norepinephrine in the intact rat brain estimated from its rate of appearance in the cerebroventricular compartment

Abstract

The apparent turnover of norepinephrine (NE) in the intact brain of urethane‐anesthetized rats was estimated in vivo from the rate of appearance of endogenous NE in the cerebroventricular compartment. Ventriculocibternal perfusion, a radioenzymatic assay for endogenous NE and isotope dilution of ³H‐NE were used to determine the rate of appearance (R_a) of NE. The effect of tranylcypromine, a monoainine oxidase (MAO) inhibitor and releasing agent on R_a of NE, was also studied. In control animals, the mean R_a value was 0.40 pmol/min. Pretreatment with tranylcypromine resulted in a threefold increase in the mean value for R_a, which was due to increased secretion of NE into the CSF. The results indicate that 90% of the NE entering the cerehroventricular compartment was removed. Pretreatment with tranylcypromine did not modify removal, thus suggesting that tranylcypromine has no effect on the physiological processes which regulate the removal of NE from the CSF.