Fate of3H‐Noradrenaline in Canine Subcutaneous Adipose Tissue1

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Abstract
Canine subcutaneous adipose tissue was isolated and perfused with defibrinated blood at a constant rate. Infused3H‐noradrenaline was taken up by the tissue and released spontaneously into blood. Following a washout period of 40 min or more, plasma samples were withdrawn. Radioactive compounds in venous plasma were separated by chromatography on alumina and Dowex. About 30 per cent of the venous radioactivity was identified as unchanged noradrenaline, about 7 per cent as normetanephrine and 14 per cent as deaminated catechols: deaminated O‐methylated metabolites accounted for about 45 per cent. This indicates the presence in adipose tissue of both monoamineoxidase and catechol‐O‐methyl‐transferase. Upon stimulation of sympathetic nerves to adipose tissue peripheral resistance increased, the3H‐presence in adipose tissue of both monoamine oxidase and catechol‐O‐methyl‐transferase. Upon cessation of the stimulation the peripheral resistance decreased and the outflow of noradrenaline metabolites increased above control values. After dihydroergotamine, nerve stimulation induced a decreased peripheral resistance, an increase of3H‐noradrenaline outflow and no change or an increase in the outflow of noradrenaline metabolites. Totally more radioactivity was released upon nerve stimulation after dihydroergotamine. The changes seen are interpreted to be associated with vascular reactions in adipose tissue.