Epinephrine effects on branchial water and urea flux in rainbow trout

In isolated trout heads, perfused at constant pressure, epinephrine (10(-6) M) was found to double water and urea efflux but increased Ringer perfusion rate by only 33%. Drastic changes in perfusion rate (by clamping) produced smaller changes of both efflux rates. Epinephrine-stimulated increase in water and urea efflux, and perfusion rate, was blocked by propranolol (beta-blocker) but not by phentolamine (alpha-blocker). Both blockers together canceled out all epinephrine effects. Epinephrine increased water influx across isolated unperfused gill arches, the effect again being blocked by propranolol but not by phentolamine. Both blockers together canceled any epinephrine effect. We conclude that epinephrine alters branchial vascular flow and functional surface area via alpha- and beta-adrenergic receptors, but also increases branchial permeability to water and probably urea, via beta-adrenergic receptors. To test the validity of the perfused head technique, water and urea efflux rates were compared with in vivo values.