Catecholamine metabolism by the perfused rainbow trout gill

Abstract

The trout gill has the capacity to influence general adrenergic activity through extraction and metabolism of circulating catecholamines (CAI; (Nekvasil and Olson, Am. J. Physiol., 1986,250:R526-R531). To further examine the metabolic process, isolated gills were perfused with M and lo-" 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 lo-' 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 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" M CAs. Dihydroxymandelic acid (DHMA) and vanillylmandelic 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" M cocaine or 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.

The adrenergic stress response in fish: control of catecholamine storage and release

“…It is evident from the studies compiled in the aforementioned review that there are marked differences in the levels of plasma catecholamines observed in different species in response to different types of stress. The dominance of either adrenaline or noradrenaline in the circulation during a stressful period is not only dependent upon storage levels [25,28,41,42,66,220] but also on the rate of metabolic degradation [56,191,192], accumulation of catecholamines into tissues [40,190,191,271,272] and the 'ability' of chromaffin cells to secrete catecholamines [239].…”

Vasculature of the fish gill: Anatomical correlates of physiological functions

“…The anatomical similarities of the mammalian pulmonary vasculature and the gill, i.e., both receive the entire cardiac output and have extensive endothelial (or pillar) cell surface area, has prompted an investigation into the ability of gill vessels to also "condition" plasma prior to systemic perfusion. Recent studies have indicated that the gill vasculature has attributes similar to the lung; i.e., it activates angiotensin I1 and extracts andlor metabolizes adenosine, catecholamines, serotonin, and bradykinin, and products of the arachidonic acid cascade (Colin and Leray, 1979;Colletti and Olson, 1988;Galardy et al, 1984;Hemker, 1987;Kullman and Olson, 1989;Lipke and Olson, 1988;Nekvasil and Olson, 1986;Olson et al, 198613;. However, unlike the pulmonary circulation, which is a single pass perfusion, blood perfusing the gill may pass through one (arterioarterial) or two (arterioarterial plus arteriovenous) microvascular networks.…”