Distribution of carbon monoxide (CO) in several tissues from Atlantic bottlenose dolphins (Tursiops truncatus)

Carbon monoxide (CO) is known as "The Silent Killer" due to its toxic effect at high concentrations, leading to an impairment in oxygen storage, delivery, and use. The cytotoxicity of CO is due to its high affinity for transition metals, such as iron, where CO outcompetes oxygen for the heme binding sites on hemoproteins in the body. CO is made in vivo in most organisms as a byproduct of heme degradation via heme oxygenase enzymes. Certain species of deep-diving marine mammals with high quantities of hemoproteins in blood and skeletal muscle have naturally elevated concentrations of CO in these tissues. To date, there exist few data on extravascular tissue CO content in wild animals. This study aims to characterize CO concentrations in nine different tissues from stranded Atlantic bottlenose dolphins (Tursiops truncatus). We found three tissues (liver, skeletal muscle, and spleen) have higher CO concentrations than other tissues. In a subset of samples from animals that tested positive for dolphin morbillivirus, the CO content in their kidney and liver was lower when compared to animals that tested negative. The mean CO concentration found in every tissue from dolphins was higher than those previously reported in healthy rodents. However, the skeletal muscle CO concentrations in dolphins from this study were much lower than those of deep-diving elephant seals. These results highlight the diversity and pattern of CO found in different tissues from bottlenose dolphins and continues to show that the heme oxygenase/carbon monoxide pathway appears to be critical for air-breathing divers.