Studies on the synthesis and subcellular distribution of dopamine in the rat adrenal medulla

Rats received intravenous injections of 3H-tyrosine and were killed at various time intervals thereafter. 3H-dopamine (DA) in the adrenals reached a maximum within 1.5 min after the administration of 3h=tyrosine. From the 15th min it disappeared with an apparent half life of 90 min. 3H-Adrenaline (A) plus 3H-noradrenaline(NA) increased much more slowly and reached a plateau 120-240 min after the injection. The approximate synthesis rate of adrenal A plus NA, calculated from the specific activity curves, ranged from 0.3 to 2.2 nmoles/h per kg b.w. The highest value was noted the first few minutes, the lowest 1-2 hrs after the administration of 3H-tyrosine. In some experiments subcellular fractionation of the adrenals was performed. In untreated animals the amount of DA and A plus NA recovered from the supernatant fraction was about 10 and 8 per cent, respectively, of the total amount recovered from the supernatant and particulate fractions. In the adrenals of animals receiving 3H-tyrosine 3.75 or 60 min beforehand these figures were significantly elevated whereas the DA and A plus NA of the particulate fraction did not deviate significantly from control values. The specific activities of 3H-DA were the same in the supernatant and particulate fractions within 3.75 min after the injection of 3H-tyrosine.