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

The blood‐brain permeabilities of L‐[³H]tyrosine and the tyrosine hydroxylase (TH) inhibitor β‐[¹⁴C]methyl‐para‐tyrosine ([¹⁴C]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 (K₁) for L‐[³H]tyrosine (6.2 ml hg‐ ⁻¹ min⁻¹) was significantly greater than the rates for L‐[¹⁴C]AMPT (2.8 ml hg⁻¹ min⁻¹) and D‐[¹⁴C]AMPT (0.8 ml hg⁻¹ min⁻¹). The apparent volume of distribution (V_f) for L‐[¹⁴C]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‐[¹⁴C]AMPT in rat brain indicates that labeled AMPT is unsuitable for the study of TH in vivo by quantitative autoradiography. © 1994 Wiley‐Liss, Inc.