Ring around the heart: an unusual feature of the crocodilian central circulatory system.

We have characterized the right (RAo) and left aortae (LAo) and their interconnections through the Foramen of Panizza (FP) and anastomosis (AN) as forming a circulatory `ring around the heart'. We look at a couple of situations where postulated blood flow through the FP, both R→L and L→R could equally well be served by flow around the ring. Closure of the LAo not only prevents the pulmonary by-pass shunt but also the possibility of oxygenated blood reaching the gut through the FR Section of the RAo, below the origin of the carotid artery, will severely restrict flow of oxygenated blood to the hind part of the body. LAo section in alligators had no effect on growth or energy conversion compared with sham operated animals indicating little selective advantage for retention of bulk flow of venous blood to the body. RAo section in caimans revealed marked effects on growth and energy conversion but too few animals were available to claim statistical significance. Nevertheless, caimans with the RAo sectioned grew much slower compared with animals with the LAo cut. The effect was generalized with no differences in the proportionate relations between head and body measurements. We speculate that the ring around the heart will function just as well as flow through the FP in effecting R→L or L→R blood transfer in the central circulation of crocodilians. [ABSTRACT FROM AUTHOR]