EFFECT OF ACUTE AND CHRONIC EPINEPHRINE ADMINISTRATION ON CLEARANCE AND METABOLISM OF [H-3] EPINEPHRINE IN TROUT (ONCORHYNCHUS-MYKISS)

Several studies have measured the rate of catecholamine clearance, met abolism, and tissue accumulation in fish. However, no information is a vailable on the effect of repeated stress or high circulating catechol amine levels on catecholamine clearance and metabolism. We measured th e clearance and metabolism of [H-3]- epinephrine (approximately 0.1 mu g.kg(-1)) in SW-acclimated rainbow trout subjected to acute (five inj ections in 1 day) and chronic (4 days; five injections per day) admini stration of 4.0 mu g.kg(-1) epinephrine or saline. In addition, a satu ration experiment, where 4.0 mu g.kg(-1) of unlabelled epinephrine was injected concurrently with [H-3]-epinephrine, investigated whether ca techolamine clearance and metabolism are affected by high circulatin l evels. Neither the rate constants for catecholamine clearance, nor the post-injection proportions of unmetabolised [H-3]-epinephrine, deamin ated [H-3]-epinephrine and O-methylated [H-3]-epinephrine were affecte d by the acute or chronic injection protocols. The concurrent injectio n of [H-3]-epinephrine and 4.0 mu g.kg(-1) of unlabelled epinephrine r esulted in an elevated postinjection H-3:C-14 ratio, but increased pro portions of O-methylated [H-3]-epinephrine and reduced proportions of unmetabolised [H-3]-epinephrine. We conclude that in fish (1) catechol amine clearance and metabolism are unlikely to be compromised by repea ted exposure to acute stressors; (2) catecholamine extraction and/or m etabolism is enhanced when circulating levels are high; and (3) there is a marked capacity to rapidly (minutes) clear and inactivate catecho lamines that are released in response to stressful stimuli.