We tend to think of carbon monoxide (CO) only in terms of being a poisonous gas. The reason for its toxicity is due to its ability to bind really tightly to our hemoglobin molecules, which prevents oxygen from being able to bind. In mammals, CO also decrease breathing rate. As you can imagine, it is a pretty terrible gas to breath in when you are a species dependent on hemoglobin for delivery of oxygen to tissues.
Did you know that CO is also produced in our bodies when heme molecules are broken down by enzymes called heme oxygenases? In a new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, researchers from the University of Ottawa wanted to know if CO produced by the body could impact breathing in zebrafish (Danio rerio) as well. The researchers found that exposure to hypoxic conditions (i.e. low oxygen) increased the activity of the hypoxia-sensitive heme oxygenase enzyme in whole larvae as well as the gills of adult fish. Like a mammal, when they exposed the fish to CO, the animals responded by decreasing breathing rate.
A bit of additional trivia: Some processors expose meat to carbon monoxide to keep it red longer, which is controversial as they can use it to mask visual detection of spoiled meats. It works by binding to the oxygen carrying molecule myoglobin in muscles and preventing its oxidation (like it does with hemoglobin). (see story from ABC news and defense of the practice from the Meat Institute).
Sources:Tzaneva V, Perry SF. Role of endogenous carbon monoxide in the control of breathing in zebrafish (Danio rerio). American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. 311(6), R1262-R1270, 2016. DOI: 10.1152/ajpregu.00094.2016
Concollato A, Bjorlykke GA, Kyamme BO, Sorheim O, Slinde E, Olsen RE. Chapter 51 – The effect of carbon monoxide on slaughter and processing of fish. Processing and Impact on Active Components in Food (ed: V Preedy). Pages 427-431, 2015.