BRAIN UPTAKE OF ALPHA-[C-14]METHYL-PARA-TYROSINE IN THE RAT

The blood-brain permeabilities of L-[H-3]tyrosine and the tyrosine hyd roxylase (TH) inhibitor alpha-[C-14]methyl-para-tyrosine ([C-14]AMPT) were determined in rat striatum, a brain region rich in TH activity, a nd in other brain regions containing relatively little TH activity. In striatum, the unidirectional clearance rate (K-1) for L-[H-3]tyrosine (6.2 ml hg(-1) min(-1)) was significantly greater than the rates for L-[C-14]AMPT (2.8 ml hg(-) min(-1)) and D-[C-14]AMPT (0.8 ml hg(-1) mi n(-1)). The apparent volume of distribution (Vf) for L-[C-14]AMPT in s triatum (72.5 +/- 4.0 ml hg(-1)) did not differ from the Vf in other b rain regions. The homogeneous distribution of L-[C-14]AMPT in rat brai n indicates that labeled AMPT is unsuitable for the study of TH in viv o by quantitative autoradiography. (C) 1994 Wiley-Liss, Inc.