Blood Flow Patterns in the Salamander, Ambystoma Tigrinum, Before, During and After Metamorphosis

The patterns of blood flow through the complex circulation of the tiger salamander, Ambystoma tigrinum, were investigated during aquatic normoxia and hypoxia by application of the microsphere technique. The distribution of differently labelled microspheres injected into the bloodstream towards the left and right atria, respectively, was used to evaluate the role of the ductus arteriosus in lung perfusion before, during and after metamorphosis, as well as the general contribution of right and left atrial outputs to the blood flow in gills and lungs in neotenic and postmetamorphic animals. The distribution patterns of radioactive microspheres among pulmonary, branchial and systemic tissues indicated that the ductus arteriosus is the major pulmonary perfusion pathway in neotenic and metamorphosing animals, whereas after metamorphosis the main perfusion pathway is down the entire length of the pulmonary artery. In neotenes, the ductus arteriosus becomes even more important during aquatic hypoxia. The anterior branchial arches receive blood richer in pulmonary venous blood than the posterior arches. Approximately 26% of left atrial output and 36% of right atrial output perfuses the brachial respiratory lamellae during normoxia in neotenes. Severe aquatic hypoxia appears to increase the fraction of cardiac output flowing to the lung and decrease the fraction flowing into the first branchial arch in neotenes. This decrease into the first arch may facilitate lung perfusion and also reduce branchial O2 loss. In postmetamorphic animals, approximately 55% of right atrial output and 32% of left atrial output is directed to the lungs. The flow patterns in postmetamorphic animals remain unaffected by aquatic hypoxia.