| Summary: | Counter to the typical idea that carbon monoxide (CO) is strictly toxic, low doses of CO 1) are naturally produced in the body through the regular turnover of heme in heme‐proteins (e.g. hemoglobin (Hb) and myoglobin), and 2) can elicit cytoprotective effects (e.g. anti‐inflammation, anti‐apoptosis). We hypothesized species with high Hb stores would have increased potential for elevated endogenous CO production. To address this, we measured levels of endogenous CO in the blood and end‐tidal breath samples of four species of marine mammals (beluga whales (n = 5), bottlenose dolphins (n = 7), elephant seals (n = 8) and killer whales (n = 9)) with a wide range of heme‐protein stores. In addition, we measured end‐tidal CO in non‐smokers from the Peruvian highlands who typically exhibit elevated Hb at high altitude (n = 48) as well as sea‐level residents (n = 18). Between the humans and marine mammals sampled in this study, there was a low Hb and low‐hypoxia group (i.e. low‐altitude humans, bottlenose dolphins and killer whales) and high‐Hb and chronic hypoxia group (i.e. high‐altitude humans, beluga whales and elephant seals). CO was measured in end‐tidal breath samples from all groups, and also in the blood from marine mammals to obtain carboxyhemoglobin (COHb) measurements. Here we show that Peruvian natives at high‐altitude exhibited significantly higher mean end‐tidal CO compared to their low‐altitude counterparts (4.8 ± 0.4 ppm vs 1.9 ± 0.7 ppm, respectively). The marine mammal species with high Hb concentrations (beluga whales and elephant seals) contained significantly higher CO in blood (1.8 ± 0.06 and 9.7 ± 1.9% COHb) and breath (7.4 ± 2.6 and 21.6 ± 2.6 ppm, respectively) than the other species which had almost undetectable levels. However, the elephant seals were unique in that they contained significantly higher mean blood and breath CO than all other groups (9.7% carboxyhemoglobin and 21.6ppm, respectively), which resembles values seen in chronic cigarette smokers (>6% carboxyhemoglobin, and >10 ...
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