The trout gill has the capacity to influence general adrenergic activity through extraction and metabolism of circulating catecholamines (CA); (Nekvasil and Olson, Am. J. Physiol., 1986, 250:R526–R531). To further examine the metabolic process, isolated gills were perfused with 10−8 M and 10−6 M norepinephrine (NEPI) or epinephrine (EPI) and effluent from the arterioarterial (AA) and arteriovenous (AV) pathways analyzed by high pressure liquid chromatography with electrochemical detection (HPLC‐EC). After 20 minutes of continuous 10−6 M NEPI perfusion, metabolites accounted for 70% and 96% of the total amines recovered in the AA and AV effluents, respectively. After 20 minutes of 10−6 M EPI perfusion, 60% and 94% of the amines in the AA and AV effluents, respectively, were metabolites. Similar results were seen during perfusion with 10−8 M CAs. Dihydroxymandelic acid (DHMA) and vanillylamandelic acid (VMA) were the major metabolites identified in gill effluent. Gills perfused with a bolus of 3H‐NEPI extracted 47% of the radiolabel. Continuous perfusion with 10−5 M cocaine or 10−5 M tyramine 30 minutes after the 3H‐NEPI pulse released 3H‐labeled and ‐unlabeled NEPI and metabolites into the AA effluent. Cocaine released more unmetabolized 3H‐NEPI than tyramine, whereas tyramine released more 3H‐labeled metabolites than cocaine. These studies indicate that the gill efficiently inactivates CAs through metabolism and that the major products formed are deaminated (DHMA) and deaminated:O‐methylated (VMA) metabolites. The gill is also able to remove NEPI from the perfusate and store it intact for up to 50 minutes. Branchial uptake of CAs in fish and pulmonary uptake of CAs in mammals appear to have basic similarities.
ASJC Scopus subject areas
- Animal Science and Zoology