Branchial Responses to Adrenaline and to Pitressin in the Eel

Perfusion experiments are described in which the effects of adrenaline and of pitressin on the gills of eels were studied. It is shown that adrenaline has a marked vasodilator effect on the gills whereas the same concentration of adrenaline has a powerful constrictor effect on the systemic vessels. Adrenaline was found to decrease or abolish completely the branchial secretion of chloride; this effect is interpreted as being due to increased permeability of the gills associated with vasodilatation. Pitressin did not appear to have any large or consistent effect either on chloride secretion or on the effective calibre of the branchial vessels. The evolutionary and physiological relations between the gills and the coronary vessels are discussed. It is suggested that the adrenaline vasodilatation of the coronary arteries may represent a phylogenetic inheritance of a specialized vascular response originally developed in the gills.