DOSE-EFFECT RELATIONSHIP OF BILIRUBIN ON STRIATAL SYNAPTOSOMES IN RATS

The uptake of tyrosine as precursor of dopamine in striatal nerve endi ngs was studied in rat striatal synaptosomes to evaluate the role of d ifferent bilirubin concentrations on this mechanism of synaptic neurot ransmission. Freshly prepared striatal synaptosomes obtained from adul t male Sprague-Dawley rats (200-300 g) were homogenized in about 25 vo l of 0.32 M sucrose and 5 nM Hepes at pH 7.4 and centrifugated at 12,0 00-16,000 rpm for 20 min. C-14 tyrosine was evaporated under N-2 and r esuspended in tyrosine 100 mu l/ml. Different concentrations of crysta lline bilirubin ranging from 70 to 140 mu M at 10-min intervals were p repared. Eighty microliters of synaptosomes were added to 5 mu l of th e different bilirubin concentrations and 20 mu l of C-14 tyrosine. The results of this study show a statistically significant correlation be tween bilirubin levels and tyrosine uptake in rat synaptosomes (p < 0. 05) supporting the hypothesis that the effect of bilirubin on neuronal excitability is dose-dependent.