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First published online October 16, 2009
Journal of Experimental Biology 212, 3553-3563 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.034595

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Surgical removal of right-to-left cardiac shunt in the American alligator (Alligator mississippiensis) causes ventricular enlargement but does not alter apnoea or metabolism during diving

John Eme^1,*, June Gwalthney¹, Jason M. Blank², Tomasz Owerkowicz¹, Gildardo Barron¹ and James W. Hicks¹

¹ Ecology and Evolutionary Biology, University of California, Irvine, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA
² Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA

^* Author for correspondence (jeme{at}uci.edu)

Accepted 28 July 2009

Crocodilians have complete anatomical separation between the ventricles, similar to birds and mammals, but retain the dual aortic arch system found in all non-avian reptiles. This cardiac anatomy allows surgical modification that prevents right-to-left (R–L) cardiac shunt. A R–L shunt is a bypass of the pulmonary circulation and recirculation of oxygen-poor blood back to the systemic circulation and has often been observed during the frequent apnoeic periods of non-avian reptiles, particularly during diving in aquatic species. We eliminated R–L shunt in American alligators (Alligator mississippiensis) by surgically occluding the left aorta (LAo; arising from right ventricle) upstream and downstream of the foramen of Panizza (FoP), and we tested the hypotheses that this removal of R–L shunt would cause afterload-induced cardiac remodelling and adversely affect diving performance. Occlusion of the LAo both upstream and downstream of the FoP for 21 months caused a doubling of RV pressure and significant ventricular enlargement (average 65%) compared with age-matched, sham-operated animals. In a separate group of recovered, surgically altered alligators allowed to dive freely in a dive chamber at 23°C, occlusion of the LAo did not alter oxygen consumption or voluntary apnoeic periods relative to sham animals. While surgical removal of R–L shunt causes considerable changes in cardiac morphology similar to aortic banding in mammals, its removal does not affect the respiratory pattern or metabolism of alligators. It appears probable that the low metabolic rate of reptiles, rather than pulmonary circulatory bypass, allows for normal aerobic dives.

Key words: alligator, diving, hypertrophy, hypometabolism, left aorta, ventricle

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