The effects of prolonged epinephrine infusion on the physiology of the rainbow trout, Salmo gairdneri. II. Branchial solute fluxes.

Rainbow trout were infused continuously for 24 h with epinephrine in order to elevate circulating levels to those measured during periods of acute extracellular acidosis (about 5 X 10(-8) mol l-1). Concomitant effects on branchial solute fluxes were evaluated. Epinephrine infusion caused complex and differential adjustments of Na+ and Cl- unidirectional fluxes (influx and efflux) resulting in a significant elevation of the arithmetic difference between Na+ and Cl- net fluxes (JnetNa+-JnetCl-). A significant correlation existed between JnetNa+-JnetCl- and net branchial acid excretion (JnetH+), thereby suggesting a role for epinephrine in piscine acid-base regulation. The stimulation of JnetH+ by epinephrine was due primarily to a reduction in the excretion of titratable acid (JTA) accompanied by non-significant changes in ammonia excretion (JAmm). The results are discussed with respect to a role for epinephrine in regulating acid-base disturbances by interacting with branchial ionic exchange mechanisms.