Vascular parameters continue to decrease post-exposure with simultaneous, but not individual exposure to BPA and hypoxia in zebrafish larvae

How fish respond to hypoxia, a common stressor, can be altered by simultaneous exposure to pollutants like bisphenol A (BPA), a plasticizer. BPA is cardiotoxic and interferes with the hypoxia inducible factor pathway (HIF-1α), therefore disrupting the hypoxic response. Co-exposure to hypoxia and BPA also causes severe bradycardia and reduced cardiac output in zebrafish larvae. The purpose of this work was to determine how the cardiovascular effects of co-exposure vary with BPA concentration and persist beyond exposure. Zebrafish embryos were exposed to 0, 0.01, 0.1, 1, and 100 μg/L of BPA during normoxia (>6.0 mg/L O₂) and hypoxia (2.0 ± 0.5 mg/L O₂) between 1 h post fertilization (hpf) and late hatching (72-96 hpf). Heart rate, cardiac output, and red blood cell (RBC) velocity were determined through video microscopy and digital motion analysis at late hatching and 10 days post fertilization (dpf), several days post exposure. In comparison to the hypoxic control, RBC velocity was 25% lower with 0.01 μg/L BPA and hypoxia at late hatching. At 10 dpf, the difference in RBC velocity between these treatments doubled, despite several days of recovery. This coincided with a 24% thinner outer diameter for caudal vein but no effect on cardiac or developmental parameters. Statistical interactions between BPA and oxygen concentration were found for arterial RBC velocity at both ages. Because the co-occurrence of both stressors is extremely common, it would be beneficial to understand how BPA and hypoxia interact to affect cardiovascular function during and after exposure.

Hypoxia exacerbates the cardiotoxic effect of the polycyclic aromatic hydrocarbon, phenanthrene in Danio rerio

The Deepwater Horizon oil spill of 2010 released a mixture of polycyclic aromatic hydrocarbons (PAHs) into the Gulf of Mexico presenting a complex exposure regime for native species. Concurrently, the Gulf has experienced an increase in hypoxic events due to agricultural runoff from the Mississippi River outflow. This combination presents a unique physiological challenge to native species and a challenge for researchers. The purpose of this study was to determine how the cardiotoxic PAH, phenanthrene interacts with hypoxia to affect the cardiovascular system of larval zebrafish (Danio rerio). We exposed zebrafish larvae to 0, 1, 100, and 1000 μg/L of phenanthrene in combination with normoxia and hypoxia. At late hatching, video of hearts and vessels were used to measure heart rate (ƒH), stroke volume (S_V), cardiac output (Q), red blood cell velocity, and caudal vessel diameter. We found that the highest concentration of phenanthrene caused a 58, 80, and 84% decrease in ƒH, Q, and arterial red blood cell velocity in normoxia and an 88, 98, and 99% decrease in hypoxia, respectively. Co-exposed larvae also experienced higher rates of edema and lordosis in addition to a 33% increase in mortality rate with co-exposure to hypoxia at the 1000 μg/L concentration of phenanthrene. At 12 dpf, baseline swimming behavior was similar between treatments indicating partial recovery from embryonic exposure. This study shows that phenanthrene decreases cardiac parameters, most significantly heart rate and that this effect is exacerbated by simultaneous exposure to hypoxia.

Bisphenol A alters the cardiovascular response to hypoxia in Danio rerio embryos

The purpose of this study was to determine if the cardiovascular response to hypoxia was altered by the presence of bisphenol A (BPA) in Danio rerio embryos. It was expected that BPA exposure would affect cardiovascular parameters during hypoxia more than normoxia due to an interaction between BPA and the hypoxia-inducible factor (HIF-1α) pathway. We demonstrate that BPA exposure has a minimal effect during normoxia but can severely affect the cardiovascular system during a hypoxic event. Cardiovascular response was measured in vivo using video microscopy and digital motion analysis. RBC density increased 35% in hypoxia alone but decreased 48% with addition of 0.25mg/L BPA. Tissue vascularization (% coverage) was unaffected by hypoxia alone but decreased 37% with addition of 0.25mg/L BPA. The diameter and RBC velocity of arteries were more sensitive than veins to BPA exposure during both normoxia and hypoxia. Arterial RBC velocity decreased 42% during normoxia and 52% during hypoxia with 1mg/L BPA. This decrease in velocity may in part be due to the 86% decrease in heart rate (ƒH) observed during co-exposure to hypoxia and 5mg/L BPA. While stroke volume (SV) was unaffected by treatment, cardiac output (Q) decreased by 69% with co-exposure. ƒH and Q were not affected by BPA exposure during normoxia. Development ultimately slowed by 146% and mortality rates were 95% during hypoxia when exposed to 5mg/L BPA. Our results show for the first time that BPA exposure alters the cardiovascular system during hypoxia more so than normoxia.