An isolated, saline-perfused trout head preparation, irrigated with hyperoxic water (PWoλ = 250 Torr), was used to assess diffusion/perfusion limitations to gill oxygen transfer. In the absence of catecholamines, increasing the perfusion flow rate caused a reduction of the partial pressure of oxygen in the dorsal aortic perfusate, indicating diffusion limitations to oxygen uptake. Physiological concentrations of epinephrine stimulated oxygen uptake in a dose-dependent fashion. Moreover, epinephrine elicited a greater effect during increased perfusion flow rate as a result of larger initial diffusion limitations, caused by the increased flow. By using a variety of adrenergic agonists and antagonists, it was demonstrated that beta-receptor stimulation enhanced oxygen uptake whereas alpha-receptor stimulation had no effect. These results are discussed with reference to changes in gill epithelial permeability to oxygen and/or surface area changes.

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