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Abstract
To protect the gill capillaries from high systolic pulse pressure, the fish heart contains a compliant non-contractile chamber called the bulbus arteriosus which is part of the outflow tract (OFT) which extends from the ventricle to the ventral aorta. Thermal acclimation alters the form and function of the fish atria and ventricle to ensure appropriate cardiac output at different temperatures, but its impact on the OFT is unknown. Here we used ex vivo pressure–volume curves to demonstrate remodelling of passive stiffness in the rainbow trout (Oncorhynchus mykiss) bulbus arteriosus following more than eight weeks of thermal acclimation to 5, 10 and 18°C. We then combined novel, non-biased Fourier transform infrared spectroscopy with classic histological staining to show that changes in compliance were achieved by changes in tissue collagen-to-elastin ratio. In situ gelatin zymography and SDS-PAGE zymography revealed that collagen remodelling was underpinned, at least in part, by changes in activity and abundance of collagen degrading matrix metalloproteinases. Collectively, we provide the first indication of bulbus arteriosus thermal remodelling in a fish and suggest this remodelling ensures optimal blood flow and blood pressure in the OFT during temperature change.
Highlights
The fish circulatory system is a single circuit
To assess whether the increased cardiac load translates to functional differences in the passive properties of the fish outflow tract (OFT) we investigated the effects of cold acclimation and warm acclimation on the compliance and connective tissue structure of the rainbow trout OFT
We have previously shown that cold acclimation increases the stiffness of the contractile chambers of the trout royalsocietypublishing.org/journal/rsif J
Summary
Blood passes through an outflow tract (OFT) leading to the ventral aorta which takes blood to the gill where it is oxygenated before continuing around the body perfusing the tissues before returning to the heart [1]. To prevent damage of the delicate gill capillary network, the OFT of teleost fish is highly specialized and is composed of a chamber called the bulbus arteriosus and bulbo-ventricular valves [2]. The bulbus arteriosus acts like a windkessel absorbing the energy of systolic blood through elastic expansion and recoil smoothing and steadying pulsatile blood flow across gill capillary networks and throughout the body [3,4,5]. The terms ‘OFT’ and ‘bulbus arteriosus’ are often used interchangeably, for clarity here we define the bulbus arteriosus as the chamber and the OFT as the whole outflow section between the ventricle and the ventral aorta
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