Improved cardiac filling facilitates the postprandial elevation of stroke volume inPython regius

Abstract

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.

Analysis of vascular mechanical properties from the yellow anaconda indicates increased elasticity and distensibility of the pulmonary artery during digestion

“…It has been suggested that specific arterial composition and microstructure confer the mechanical properties that enable arteries of different vertebrates to perform similarly at their normal in vivo pressures (Gibbons and Shadwick, 1989;Shadwick, 1999). The snake vascular system experiences further mechanical stress during the postprandial period as a result of the concomitant rise in both heart rate and stroke volume (Secor et al, 2000;Secor and White, 2010;Zerbe et al, 2011;Enok et al, 2016). These adjustments are necessary to match the severalfold increase in metabolism over the course of numerous days following ingestion of large meals (Andrade et al, 1997;Andersen et al, 2005;Gavira and Andrade, 2013) along with the concomitant tissue growth (Secor and Diamond, 1998).…”

Embryonic hypoxia programmes postprandial cardiovascular function in adult common snapping turtles (Chelydra serpentina)

“…For reptiles, feeding elicits marked elevations in oxygen consumption rate ( _ V O 2 ) that last for several hours (Secor and Diamond, 1999;Hicks et al, 2000;Wang et al, 2001a;Overgaard et al, 2002a;Hicks and Bennett, 2004;Enok et al, 2013;Wearing et al, 2016). This postprandial increase in oxygen demand necessitates increased _ Q to sufficiently supply tissues with oxygen Secor et al, 2000;Wang et al, 2001a;Hicks and Bennett, 2004;Andersen et al, 2005;Secor and White, 2010;Enok et al, 2012Enok et al, , 2013Enok et al, , 2016Wearing et al, 2016). In terrestrial vertebrates, _ Q can be modulated by changes in heart rate ( f H ) and/or V S .…”

Autoregulation of cardiac output is overcome by adrenergic stimulation in the anaconda heart

“…Sandblom et al, 2005;Skals et al, 2005Skals et al, , 2006Enok et al, 2016). By mobilizing blood from the veins, preload pressure may be maintained, or even increased, despite the increased heart rate during activity (Sandblom et al, 2005;Skals et al, 2006).…”