The relationship between hypoxia exposure and circulating cortisol levels in social and solitary African mole-rats: An initial report
Hart, Daniel W.; Bennett, Nigel C.; Best, Carol; van Jaarsveld, Barry; Cheng, Hang; Ivy, Catherine M.; Kirby, Alexia M.; Munro, Daniel; Sprenger, Ryan J.; Storey, Kenneth B.; Milsom, William K.; Pamenter, Matthew E.
(2023) General and Comparative Endocrinology, volume 339
(Article)
Abstract
Hypoxemia from exposure to intermittent and/or acute environmental hypoxia (lower oxygen concentration) is a severe stressor for many animal species. The response to hypoxia of the hypothalamic-pituitary-adrenal axis (HPA-axis), which culminates in the release of glucocorticoids, has been well-studied in hypoxia-intolerant surface-dwelling mammals. Several group-living (social) subterranean species, including most
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African mole -rats, are hypoxia-tolerant, likely due to regular exposure to intermittent hypoxia in their underground bur-rows. Conversely, solitary mole-rat species, lack many adaptive mechanisms, making them less hypoxia-tolerant than the social genera. To date, the release of glucocorticoids in response to hypoxia has not been measured in hypoxia-tolerant mammalian species. Consequently, this study exposed three social African mole-rat species and two solitary mole-rat species to normoxia, or acute hypoxia and then measured their respective plasma gluco-corticoid (cortisol) concentrations. Social mole-rats had lower plasma cortisol concentrations under normoxia than the solitary genera. Furthermore, individuals of all three of the social mole-rat species exhibited signifi-cantly increased plasma cortisol concentrations after hypoxia, similar to those of hypoxia-intolerant surface -dwelling species. By contrast, individuals of the two solitary species had a reduced plasma cortisol response to acute hypoxia, possibly due to increased plasma cortisol under normoxia. If placed in perspective with other closely related surface-dwelling species, the regular exposure of the social African mole-rats to hypoxia may have reduced the basal levels of the components for the adaptive mechanisms associated with hypoxia exposure, including circulating cortisol levels. Similarly, the influence of body mass on plasma cortisol levels cannot be ignored. This study demonstrates that both hypoxia-tolerant rodents and hypoxia-intolerant terrestrial laboratory-bred rodents may possess similar HPA-axis responses from exposure to hypoxia. Further research is required to confirm the results from this pilot study and to further confirm how the cortisol concentrations may influence responses to hypoxia in African mole-rats.
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Keywords: Glucocorticoids, Hypoxia-tolerance, Naked mole-rats, Stress, Subterranean, Endocrinology, Animal Science and Zoology
ISSN: 0016-6480
Publisher: Academic Press Inc.
Note: Funding Information: This study was funded by SARCHI Chair of Mammal Behavioural Ecology and physiology to N.C.B. (64756) and a National Geographic Society Explorers Grant to M.E.P (WW-060R-17), Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants (04229-2015 to M.E.P., 22R87150 to W.K.M., and 04733-2020 to K.B.S.), and Canada Research Chairs (950-230954) to M.E.P and K.B.S. Funding Information: We thank Nature Conservation authorities for the collection of wild specimens and Mr. John Duckitt, Waylands. In addition, we want to thank Dr Phoebe Edwards and the anonymous reviewer of this study for their helpful and constructive comments. This study was funded by SARCHI Chair of Mammal Behavioural Ecology and physiology to N.C.B. (64756) and a National Geographic Society Explorers Grant to M.E.P (WW-060R-17), Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants (04229-2015 to M.E.P. 22R87150 to W.K.M. and 04733-2020 to K.B.S.), and Canada Research Chairs (950-230954) to M.E.P and K.B.S. All experimental procedures conducted in Canada were approved by the University of Ottawa Animal Care Committee (protocol #2535), in accordance with the Animals for Research Act and by the Canadian Council on Animal Care. Trapping and experiments done in South Africa were conducted under appropriate permits issued by Cape Nature Conservation and the Department of Nature Conservation in the Western Cape, Republic of South Africa (CN44-31–2285) and with experimental procedures approved by the animal ethics committee of the University of Pretoria (EC069-17). Publisher Copyright: © 2023 The Authors
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