Key result
Physical vascular characteristics primarily drive cane toad net cardiac shunts rather than physiological regulation.
Why the study?
The contribution of passive physical characteristics versus autonomic regulation to net cardiac shunts in anuran amphibians was not well understood.
The net cardiac shunt in the cane toad is predicted primarily by the passive physical characteristics of the parallel pulmonary and systemic vascular circuits rather than physiological autonomic regulation.
Highlights physical vascular properties over regulation in amphibian shunts; leaves open relevance to human cardiac physiology.
Amphibians have a single ventricle and common conus arteriosus that produces an equal pressure to the parallel pulmocutaneous and systemic vascular circuits. The distribution of blood flows between the pulmocutaneous (Qpul) and systemic (Qsys) circuits (net cardiac shunt) varies with a number of environmental conditions and behaviours; although autonomic regulation of pulmonary vascular resistance conductance has been emphasized, little attention has been paid to the possible contribution of the passive physical characteristics of the two circuits to pressure changes associated with variation in cardiac output. In this study, we re-analysed three recent studies that recorded net cardiac shunts in the cane toad (Rhinella marina) under a variety of conditions and treatments. In all three studies, Qpul and Qsys were linearly related to cardiac output (Qtot), but the slope was threefold higher for Qpul compared with Qsys as predicted by relative conductance increases associated with increases in pressure from perfused preparations where autonomic regulation and humoral control were eliminated. Our analysis indicates that the net cardiac shunt in the cane toad is predicted primarily by the physical, rather than physiological, characteristics of the parallel pulmonary and systemic vascular circuits.
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Hillman et al. (2014) studied Net cardiac shunts in cane toads (Rhinella marina). Physical characteristics of parallel pulmonary and systemic vascular circuits vs. Physiological (autonomic) regulation was evaluated on Relationship between Qpul/Qsys and cardiac output (Qtot). In the cane toad, the net cardiac shunt is predicted primarily by the physical characteristics of the parallel pulmonary and systemic vascular circuits rather than physiological regulation.
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