ABSTRACT
The presence of cardiac shunts in ectothermic tetrapods is thought to be consistent with active vascular modulations for proper hemodynamic support. Local control of blood flow modulates tissue perfusion and thus systemic conductance (Gsys) is assumed to increase with body temperature (Tb) to accommodate higher aerobic demand. However, the general increase of Gsys presses for a higher right-to-left (R–L) shunt, which reduces arterial oxygen concentration. In contrast, Tb reduction leads to a Gsys decrease and a left-to-right shunt, which purportedly increases pulmonary perfusion and plasma filtration in the respiratory area. This investigation addressed the role of compensatory vascular adjustments in the face of the metabolic alterations caused by Tb change in the South American rattlesnake (Crotalus durissus). Cardiovascular recordings were performed in decerebrated rattlesnake preparations at 10, 20 and 30°C. The rise in Tb increased metabolic demand, and correlated with an augmentation in heart rate. Although cardiac output increased, systemic stroke volume reduced while pulmonary stroke volume remained stable. Although that resulted in a proportionally higher increase in pulmonary blood flow, the R–L shunt was maintained. While the systemic compliance of large arteries was the most relevant factor in regulating arterial systemic blood pressure, peripheral conductance of pulmonary circulation was the major factor influencing the final cardiac shunt. Such dynamic adjustment of systemic compliance and pulmonary resistance for shunt modulation has not been demonstrated before and contrasts with previous knowledge on shunt control.
Footnotes
Author contributions
Conceptualization: S.A.C., C.A.C.L.; Methodology: S.A.C., C.A.C.L.; Validation: S.A.C., C.A.C.L.; Formal analysis: S.A.C., J.V.P.; Investigation: S.A.C.; Resources: C.A.C.L.; Data curation: S.A.C., C.A.C.L.; Writing - original draft: S.A.C., J.V.P.; Writing - review & editing: T.W., C.A.C.L.; Visualization: S.A.C., T.W., C.A.C.L.; Supervision: C.A.C.L.; Project administration: C.A.C.L.; Funding acquisition: C.A.C.L.
Funding
S.A.C. received a PhD grant from the National Council for Scientific and Technological Development (Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq 142386/2020-0). T.W. is supported by the NOVO Nordisk Foundation (Novo Nordisk Fonden).
Data availability
All relevant data can be found within the article and its supplementary information.