Brain uptake of α‐[ 14 C]methyl‐ para ‐tyrosine in the rat

The blood‐brain permeabilities of L‐[ 3 H]tyrosine and the tyrosine hydroxylase (TH) inhibitor β‐[ 14 C]methyl‐ para ‐tyrosine ([ 14 C]AMPT) were determined in rat striatum, a brain region rich in TH activity, and in other brain regions containing relatively little TH activity. In striatum, the unidirectional clearance rate (K 1 ) for L‐[ 3 H]tyrosine (6.2 ml hg‐ −1 min −1 ) was significantly greater than the rates for L‐[ 14 C]AMPT (2.8 ml hg −1 min −1 ) and D‐[ 14 C]AMPT (0.8 ml hg −1 min −1 ). The apparent volume of distribution (V f ) for L‐[ 14 C]AMPT in striatum (72.5 ± 4.0 ml hg‐ 1 ) did not differ from the V f in other brain regions. The homogeneous distribution of L‐[ 14 C]AMPT in rat brain indicates that labeled AMPT is unsuitable for the study of TH in vivo by quantitative autoradiography. © 1994 Wiley‐Liss, Inc.