Differences in amine storage in rat heart and brain

1 The characteristics of storage of amphetamine-releasable amine in rat heart and brain were studied in vitro with labelled and unlabelled metaraminol ([(3)H]-MA and MA).2 In one series of experiments, heart and brain slices were incubated with [(3)H]-MA prior or subsequent to incubation with the same concentration of MA.3 When brain slices, thus treated, were subjected successively to field stimulation and to amphetamine, it was found that the ratio of [(3)H]-MA release by field stimulation to release by amphetamine was dependent upon the order in which brain tissue was exposed to [(3)H]-MA and MA.4 With heart slices, on the other hand, the field stimulation/amphetamine ratio of [(3)H]-MA release remained the same whether the tissue was exposed to [(3)H]-MA before or after MA.5 The (+)-isomer of amphetamine released three to four times more [(3)H]-MA from brain slices than did the (-)-isomer, while the isomers were equipotent with regard to [(3)H]-MA release from heart slices.6 Amphetamine-induced [(3)H]-MA release from heart slices was unaffected by the presence of alpha-methyl-p-tyrosine, while release from brain slices was inhibited.7 On the basis of the foregoing results it appears that amine storage differs in brain and heart, with brain exhibiting more than one functional amine pool.