The effects of vasoactive agents on the functional surface area of isolated-perfused gills of rainbow trout

1.The relative functional surface area of isolated-perfused gills was evaluated by measuring the influx of¹⁴C-urea, a passively diffusing molecule.2.The catecholamines, norepinephrine and epinephrine, increase functional gill surface area and decrease overall branchial vascular resistance.3.Surface area and resistance effects of adrenergic agonists and blocking agents demonstrated the presence of both a and ß adrenergic receptors in rainbow trout gills.4.Stimulation of a adrenergic receptors increased both functional surface area and branchial vascular resistance, while ß adrenergic receptor stimulation increased functional surface area but decreased branchial vascular resistance.5.Acetylcholine decreased functional gill surface area and increased overall branchial vascular resistance.6.The data presented strongly indicate that the functional surface area of rainbow trout gills can be regulated by changing perfusion pathway with adjustments in the relative vascular resistance across the different pathways.