To accommodate the pronounced metabolic response to digestion, pythons increase heart rate and elevate stroke volume, where the latter has been ascribed to a massive and fast cardiac hypertrophy. However, numerous recent studies show that heart mass rarely increases, even upon ingestion of large meals, and we therefore explored the possibility that a rise in mean circulatory filling pressure (MCFP) serves to elevate venous pressure and cardiac filling during digestion. To this end, we measured blood flows and pressures in anaesthetized Python regius. The anaesthetized snakes exhibited the archetypal tachycardia as well as a rise in both venous pressure and MCFP that fully account for the approximate doubling of stroke volume. There was no rise in blood volume and the elevated MCFP must therefore stem from increased vascular tone, possibly by means of increased sympathetic tone on the veins. Furthermore, although both venous pressure and MCFP increased during volume loading, there was no evidence that postprandial hearts were endowed with an additional capacity to elevate stroke volume. In vitro measurements of force development of paced ventricular strips also failed to reveal signs of increased contractility, but the postprandial hearts had higher activities of cytochrome oxidase and pyruvate kinase, which probably serves to sustain the rise in cardiac work during digestion.
The authors declare no competing or financial interests.
All authors were involved in conceiving and designing the study and partook in the experiments and the data analysis. S.E. collated the information and wrote the manuscript, with input from the other authors, who also approved its final version.
This study was supported by the Danish Natural Science Research Council, the CNPq and FAPESP through the INCT of Comparative Physiology.
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.142729.supplemental
- Received May 12, 2016.
- Accepted July 18, 2016.
- © 2016. Published by The Company of Biologists Ltd