AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 3 526-R531, Copyright © 1986 by American Physiological Society
Extraction and metabolism of circulating catecholamines by the trout gill
N. P. Nekvasil and K. R. Olson
Extraction and metabolism of [3H]-norepinephrine (NE) and [3H]epinephrine
(E) by the respiratory (efferent branchial) and filamental (venous)
vasculature of the trout gill were examined using an isolated perfused arch
technique in which outflow from the two circulations was separated.
Deaminated and O-methylated metabolites in the effluent were identified by
ion-exchange chromatography. Metabolism by tissue homogenates was also
measured. Gill homogenates deaminate catecholamines (CAs) faster than
homogenates of liver, kidney, and skeletal muscle; branchial O-methylation
was comparable to that of liver and kidney. The perfused gill extracted 60%
of a NE pulse and 47% of an E pulse. During continuous CA perfusion the
gill removed greater than 30% of the NE from the circulation through
extraction and metabolism; only 7% of the E was removed. The gill venous
system extracts and metabolizes more CAs than the efferent. NE is the
preferred substrate for extraction and metabolism. A mechanism is proposed
whereby high circulating CA levels, common during stress, are maintained
through CA-induced reduction in venous blood flow. After the stress is
alleviated, CA levels begin to fall, flow to the venous pathway increases,
and the rate of inactivation of circulating CAs increases.
