Intrauterine growth restriction induces up-regulation of cerebral aromatic amino acid decarboxylase activity in newborn piglets: [¹⁸F]fluorodopa positron-emission-tomographic study

There is evidence that intrauterine growth restriction (IUGR) is associated with altered dopaminergic function in the immature brain. However, the relevant enzyme activities have not been measured in the living neonatal brain together with brain oxidative metabolism. Therefore ¹⁸F-labelled 6-fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) was used together with positron-emission-tomography to estimate the activity of the aromatic amino acid decarboxylase in the brain of 10 newborn IUGR piglets (2 to 5 days old; body weight 908±109g) and in 10 normal-weight (3 to 5 d old; body weight 2142±373g) newborn piglets. The regional transport of FDOPA to the brain and the clearance rate of labeled metabolites from brain tissue were broadly similar in the two groups. However, the regional rate constant for back flux from the brain was markedly increased in IUGR piglets for striatum (72%) and frontal cortex (83%) (p < 0.05). Furthermore, the rate constant for conversion of FDOPA to fluordopamine was markedly increased (between 48 % in cerebellum and 91 % in mesencephalon, p < 0.05) in all brain regions of IUGR piglets studied.
Thus, it is suggested that IUGR induces an up-regulation of amino acid decarboxylase activity that is not related to alterations in brain oxidative metabolism.