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

Rats received intravenous injections ofH-tyrosine and were killed at various time intervals thereafter.H-dopamine (DA) in the adrenals reached a maximum within 1.5 min after the administration ofH-tyrosine. From the 15th min it disappeared with an apparent half life of 90 min.H-Adrenaline (A) +H-noradrenaline(NA) increased much more slowly and reached a plateau 120-240 min after the injection. The approximate synthesis rate of adrenal A+NA, calculated from the specific activity curves, ranged from 9.3 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 ofH-tyrosine. In some experiments subcellular fractionation of the adrenals was performed. In untreated animals the amount of DA and A+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 receivingH-tyrosine 3.75 or 60 min beforehand these figures were significantly elevated whereas the DA and A+NA of the particulate fraction did not deviate significantly from control values. The specific activities ofH-DA were the same in the supernatant and particulate fractions within 3.75 min after the injection ofH-tyrosine. [ABSTRACT FROM AUTHOR]