Impact of hibernation on endogenous carbon monoxide concentrations and heme oxygenase activity in thirteen lined ground squirrels ( <i>Ictidomys tridecemlineatus</i> )

The thirteen-lined ground squirrel ( Ictidomys tridecemlineatus ) experiences periods of torpor in winter months that are associated with reduced body temperature, metabolism, and a significant decrease in heart rate that leads to blood flow reduction [ischemia (I)] to certain tissues. Between torpor events, brief arousals are shown by increased body temperature, metabolic rate, and reperfusion (R) to tissues. These I/R events cause damage in most mammalian tissues, but low to moderate levels of carbon monoxide (CO) have been shown to alleviate injuries in tissues exposed to frequent I/R events. High concentrations of endogenously produced CO have also been reported in the blood and tissues of deep-diving mammals that routinely experience I/R in their tissues. Heme oxygenase (HO) enzymes break down heme, producing CO as a byproduct. We examined CO concentrations and HO activity in tissues from 15 squirrels experiencing consecutive torpor for 1, 3, 4, or 10 days. Lung CO concentrations after 1 day of torpor (8.2 ± 2.3 pmol/mg) increased after 10 days in torpor (14.9 ± 5.2 pmol/mg). Conversely, HO activity in the lung on day 1 of torpor (10.2 ± 2.6 nmol/hr/g) decreased after 10 days in torpor (3.6 ± 1.2 nmol/hr/g). The spleen, an organ involved in erythrocyte turnover, had the highest average CO content among tissues (29.9 ± 7.0 pmol/mg), though values decreased with increased time in torpor (16.9 ± 8.2 pmol/mg). Similarly, HO activity in the spleen was highest in day 1 of torpor (13.5 ± 4.4 nmol/hr/g) and decreased with increased time spent in torpor (11.6 ± 3.7 nmol/hr/g). These findings are the first to report variations in CO and corresponding HO activity in hibernating mammals, providing insight into the physiological significance of this cytoprotective gas during hibernation. 1. NSF Grant (#1927616) 2. Hozier Undergraduate Research Fellowship 2024-2025 3. UNCW Bio and Marine Bio Travel Grant 4. UNCW CSURF Supplies Grant Summer 2023 and Fall 2024 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.