What Role Does Central Venous Pressure Play in Supporting Cardiac Function in Nile Tilapia (Oreochromis niloticus) Exposed to Environmental Challenges?
This work examined the role of central venous pressure (CVP), an understudied component of cardiac regulation in fishes, in tilapia faced with a number of environmental challenges. First, we measured the heart rate (fH), cardiac output (Q), stroke volume (SV) and CVP of 30℃-acclimated fish, and those acutely exposed to 24℃, following titrations of zatebradine hydrocholoride (i.e., a pharmacological agent that decreases intrinsic fH). As predicted, fH and Q were ~40% lower in the acutely cooled fish (Q10 ~ 2.3) and both groups had very comparable (i.e., within 10%) values for SV (i.e., SV was temperature insensitive). Interestingly, the CVP of fish at 24℃ was higher than that in 30℃-acclimated fish across all concentrations of zatebradine (i.e., CVP increased from 0.04–0.11 kPa vs. -0.09–0.07 kPa, respectively, as fH was reduced), and this was reflected in a right-shifted relationship between CVP and SV for the 24℃ fish. These data suggest that the acutely cooled tilapia required a higher CVP to attain a similar SV as compared to 30℃ conspecifics. Ongoing experiments are now being performed on 25℃-acclimated tilapia to measure the same cardiovascular parameters (with the addition of oxygen consumption and tissue-oxygen extraction) when: i) exposed to critical thermal maximum (CTMax) and minimum (CTMin) tests at normoxia (100% air sat.); and ii) when exposed to acute/severe hypoxia (30% air sat.) followed by a CTMax test.