Vascular resistance and vasoactivity of gills and pulmonary artery of the salamander,Ambystoma tigrinum

Abstract

In order to understand the blood flow patterns and their regulation in the gills and pulmonary artery ofAmbystoma tigrinum, the vascular resistance and vasoactivity of the two major branchial perfusion pathways and a vascular plexus in the pulmonary artery were investigated using an isolated-tissue perfusion method. Acetylcholine and epinephrine were both pressor agents in all three vascular segments. Angiotensin II also constricted the branchial respiratory vasculature. Norephinephrine was primarily a vasodilator in the branchial respiratory vasculature, however, it had no effect on the shunt vessels of the gill or the pulmonary arterial plexus. Both gill circulations were insensitive to alterations in CO2 and pH. Anoxia produced a slight vasodilation of the branchial respiratory vessels but had no effect on the shunt vasculature. Mild hypoxia had no effect on either branchial circulations. The results suggest that: (1) blood flow through the respiratory section of the gill may vary between 8 and 47% of total gill flow, (2) the major perfusion pathway to the lung is probably from the efferent artery of the third gill through the ductus arteriosus and then into the pulmonary artery, (3) O2, CO2 and pH exert no local control of branchial perfusion, (4) both cholinergic and adrenergic regulation of branchial and proximal pulmonary arterial vascular resistance is possible, (5) a rise in circulating norepinephrine should increase blood flow to the respiratory section of the gill.