Plasma clearance, metabolism, and tissue accumulation of 3H-labeled catecholamines in trout

Abstract

Plasma clearance, metabolism, and tissue accumulation of [3H]norepinephrine (NE) and [3H]epinephrine (E) were measured after injection into the dorsal aorta of chronically catheterized trout, Salmo gairdneri. Sucrose, an inert volume marker, was injected with the catecholamines (CAs). Ion-exchange chromatography was used to separate unmetabolized CAs from deaminated and O-methylated metabolites in plasma. Both CAs are cleared from plasma at an exponential two-component rate. By 10 min postinjection, CA-specific extraction lowered plasma [3H]NE by 65% and [3H]E by 50%. Over 80% of the 3H remaining in plasma 10 min after injection was metabolized to O-methylated and deaminated products. Thus trout are able to quickly and efficiently lower circulating CA levels through tissue accumulation and metabolism. Kidney, liver, spleen, and atrium accumulate more CA than other tissues, although most tissues bind CA to some extent. Gills preferentially accumulate CAs over sucrose. Skeletal muscle has a low affinity for CAs but by virtue of its large mass may be an important organ in CA metabolism. NE is removed from the circulation faster, and more NE is bound to tissues than E. A blood-brain barrier for E but not NE was observed.