Abstract
A technique of perfusing the isolated head of trout with a constant-fluid flow was used to study adrenergic factors controlling the vasomotricity of the gill. The use of adrenergic blockers (phentolamine 10(-4) M and propranolol 10(-4) M) enabled the vascular effect of epinephrine to be split into two components: an alpha-vasoconstrictor effect superimposed upon the dominant beta-vasodilator effect. Effect alpha appears more rapidly than effect beta and causes an initial vasoconstriction. Under constant-flow perfusion the effect of epinephrine on the efferent arterial and venous flows is a diminution of the venous flow and an increase of the arterial. This is the result of closure of the anastomoses between the efferent artery and the central compartment of the filament. It was shown that only alpha-vasoconstrictor adrenoreceptors occur in this region.
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