Vagal tone regulates cardiac shunts during activity and at low temperatures in the South American rattlesnake, Crotalus durissus.
The undivided ventricle of non-crocodilian reptiles allows for intracardiac admixture of oxygen-poor and oxygen-rich blood returning via the atria from the systemic circuit and the lungs. The distribution of blood flow between the systemic and pulmonary circuits may vary, based on differences between systemic and pulmonary vascular conductances. The South American rattlesnake, Crotalus durissus, has a single pulmonary artery, innervated by the left vagus. Activity in this nerve controls pulmonary conductance so that left vagotomy abolishes this control. Experimental left vagotomy to abolish cardiac shunting had no effect on long-term survival and failed to identify a functional role in determining metabolic rate, growth or resistance to food deprivation. Accordingly, the present investigation sought to evaluate the extent to which cardiac shunt patterns are actively controlled during changes in body temperature and activity levels. We compared hemodynamic parameters between intact and left-vagotomized rattlesnakes held at different temperatures and subjected to enforced physical activity. Increased temperature and enforced activity raised heart rate, cardiac output, pulmonary and systemic blood flow in both groups, but net cardiac shunt was reversed in the vagotomized group at lower temperatures. We conclude that vagal control of pulmonary conductance is an active mechanism regulating cardiac shunts in C. durissus.
Department of Zoology, State University of São Paulo (UNESP), Rio Claro, SP, Brazil. renatofilogonio@gmail.com.|Zoophysiology, Department of Bioscience, Aarhus University, 8000, Aarhus C, Denmark. renatofilogonio@gmail.com.
Renato
http://orcid.org/0000-0002-5436-7102
R
Filogonio
Zoophysiology, Department of Bioscience, Aarhus University, 8000, Aarhus C, Denmark.
Tobias
T
Wang
Department of Zoology, State University of São Paulo (UNESP), Rio Claro, SP, Brazil.|School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK.
Edwin W
EW
Taylor
Department of Zoology, State University of São Paulo (UNESP), Rio Claro, SP, Brazil.
Augusto S
AS
Abe
Department of Physiological Sciences, Federal University of São Carlos (UFSCar), São Carlos, SP, Brazil.
Cléo A C
CA
Leite
D000818:Animals; D002302:Cardiac Output; D003326:Coronary Circulation / Q000502:physiology*; D017839:Crotalus / Q000502:physiology*; D006339:Heart Rate; D013696:Temperature; D014628:Vagotomy; D014630:Vagus Nerve / Q000502:physiology* / Q000601:surgery
Arterial pressure; Blood flow; Cardiac shunt; Reptiles; Snakes; Vagus nerve; Vascular regulation