RT Journal Article SR Electronic T1 ESTIMATION OF IN VIVO DOPAMINE-β-HYDROXYLASE ACTIVITY IN RAT BRAIN JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 230 OP 240 VO 186 IS 2 A1 JON M. STOLK YR 1973 UL http://jpet.aspetjournals.org/content/186/2/230.abstract AB A technique for estimating in vivo dopamine-β-hydroxylase activity in rat brain is described. The procedure involves the intracisternal injection of known amounts of radioactive dopamine and measurement of the amount of norepinephrine formed and remaining in brain at timed intervals thereafter. Investigation of product (norepinephrine) formation over a wide range of injection dopamine doses revealed a highly reproducible relationship. Subcellular distribution of the formed product was identical with that of endogenous norepinephrine. Pretreatment with 6-hydroxydopamine or U-14,624, a known dopamine-β-hydroxylase inhibitor, caused a marked reduction in norepinephrine formation that paralleled the extent of endogenous norepinephrine depletion. Regional distribution studies revealed that the cerebellum, medulla-pons, diencephalon and telencephalon, in decreasing order, all contributed to measured product formation. With the exception of tile cerebellum, the distribution of dopamine-β-hydroxylase activity measured in vivo reflected that observed with in vitro assay procedures. It is concluded that injected doses of labeled dopamine below 8 mµg are valid for assessing in situ dopamine-β-hydroxylase activity. Although higher doses of intracisternally injected precursor may be useful in estimating levels of enzyme, as opposed to enzyme activity. the presence of potential complicating variables precluded further definition. © 1973 by The Williams & Wilkins Co.