The Interaction of Cardiac Shunting and Metabolic Rate: Triggering Hypometabolism During Diving

University Of California-Irvine, Irvine CA

Investigators

Abstract

Comparative biologists have known for more than 150 years that the anatomy of the reptilian heart results in the potential for cardiac shunts (mixing of oxygen poor and oxygen rich blood). Cardiac shunts can be defined as right-to-left (R-L oxygen poor blood bypasses the lung) or left-to-right (L-R oxygen rich blood recirculates through the lung). In several reptiles an R-L cardiac shunt can develop during diving resulting in a rapid reduction of the blood oxygen levels. The physiological benefits of this type of cardiovascular regulation have remained elusive and speculative. The proposed research by Dr. Hicks will investigate the hypothesis that reductions in blood oxygen levels, resulting from the development of a R-L cardiac shunt, triggers a reduction in metabolism. The reduction in metabolism is referred to as a "hypometabolic state" and can have several physiological benefits, particularly during prolonged diving. The proposed research will test the generality of the hypothesis by investigating the effects of cardiac shunting on metabolism in the freshwater turtle, Trachemys scripta, American Alligator, Alligator mississippiensis and green iguana, Iguana iguana. These species possess several characters that make them good experimental models that include; 1) all exhibit diving behavior, either voluntarily or during escape behavior, 2) all species are readily available and 3) they are large enough to support the required physiological instrumentation. The proposed research will experimentally test a potential physiological function that results from the unique cardiovascular "design" of reptiles and will provide insights into the functional consequences of retaining the capacity for cardiac shunting.