Inhibitory effects of desmethylimipramine, metanephrine and normetanephrine on the neuronal and extraneuronal accumulation of catecholamines in fish spleen.

The effect of desmethylimipramine, metanephrine and normetanephrine on the neuronal and extraneuronal accumulation of radiolabelled adrenaline and noradrenaline were studied in the perfused spleen of the teleost fish, Atlantic cod, Gadus morhua. Desmethylimipramine was found to be a potent inhibitor for the neuronal accumulation of both adrenaline and noradrenaline in the cod spleen, suggesting similarities with the neuronal uptake mechanism in mammals. Metanephrine was found to inhibit the extraneuronal accumulation of noradrenaline, though not that of adrenaline, while normetanephrine did not change the extraneuronal accumulation of any of the catecholamines. Both metanephrine and normetanephrine were more potent neuronal uptake blockers than extraneuronal. Metanephrine inhibited only the neuronal accumulation of adrenaline, while normetanephrine inhibited neuronal accumulation of both catecholamines. It is concluded that adrenaline and noradrenaline accumulate differently in the adrenergic neurons of the cod spleen as was suggested earlier for noradrenaline and tyramine (Nilsson & Holmgren 1976). It is also evident from the study that the uptake mechanisms or accumulation of catecholamines in lower vertebrates such as fish may be different from corresponding mechanisms in mammals.