The effects of chronic hypoxia and nitric oxide on myocardial contractility in steelhead trout (Onchorhynchus mykiss)

Carnevale, Christian (2019) The effects of chronic hypoxia and nitric oxide on myocardial contractility in steelhead trout (Onchorhynchus mykiss). Masters thesis, Memorial University of Newfoundland.

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Abstract

Environmental hypoxia has been intensifying and spreading in recent years due to climate change, and there is accumulating evidence that the cardiac function of hypoxia-intolerant fish is negatively affected by long-term exposure to low oxygen conditions. However, the cause of this reduced heart performance has not been conclusively identified, and it is unknown whether nitric oxide (NO)-mediated effects are involved. This thesis examined how chronic hypoxia (> 8 weeks at ~8 kPa O₂) influenced the contractility (i.e., work and power) of steelhead trout (Oncorhynchus mykiss) spongy myocardial strips upon exposure to graded hypoxia (21 – 1.5 kPa), and influenced NO-mediated performance. Hypoxic-acclimated strips produced less shortening power (by ~35%) as compared to those from normoxic-acclimated conspecifics, but experienced similar reductions in contractility during acute hypoxia and did not recover as well upon re-oxygenation. The effects of NO on myocardial function were not greatly affected by hypoxic-acclimation, but were found to be highly dependent on contraction frequency and strain.

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