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Introduction: To objectify the oxygen debt in dogs with brachycephalic upper respiratory syndrome, eight mesocephalic dogs were subjected to a short running test on four test days and eight brachycephalic dogs on one test day. Blood samples were taken before and immediately after exercise and after 2 and 4 hours to assess cellular oxygenation. For this purpose, two available hypoxia markers, vascular endothelial growth factor (VEGF) and erythropoietin (EPO), were measured. The repeatability of the measurements was checked in the mesocephalic dogs. While VEGF measurement was repeatable over the 4 days of measurement, the EPO measurement was not. The VEGF basal values of the mesocephalic and brachycephalic dogs did not differ (7.6 ± 4.4 pg/ml and 6.9 ± 4.0 pg/ml, respectively). The measurement 4 hours after the running test showed significant differences. The VEGF value in the mesocephalic dogs increased by 42 % to 10.8 ± 4.7 pg/ml, while in the brachycephalic dogs it increased by 220 % to 22.1 ± 15.3 pg/ml. The EPO measurements showed a significant difference between the mesocephalic and brachycephalic dogs at all blood collection times; The basal value in mesocephalic dogs was approx. three times higher than in brachycephalic dogs (30.1 ± 22.6 mU/ml or 11.4 ± 3.5 mU/ml). However, the difference was not significant due to the large scatter in the mesocephalic dogs (p > 0.05). In contrast to the VEGF value, the EPO value did not change over the measurement period. The study shows that the presented method can be used together with the VEGF value for scientific and breeding purposes.

Mauremys mutica is a widely cultured pond turtle in China that can hold its breath underwater for up to 7 h. However, the adaptive mechanism of this hypoxia-resistant phenotype remains unknown. In the present study, no M. mutica died until 6 h of hypoxic stress. Inflammation was observed in the lungs of dead individuals along with a lung cell apoptosis rate of 12.3% in the death group, which was about six times that of the survival group. Transcriptome sequencing produced 379,659,748 clean reads, and 38,981 genes were obtained. A total of 1566, 1555 and 756 differentially expressed genes (DEGs) were detected between the survival group and the death group, the survival group and the control group, and the death group and the control group, respectively. And the DEGs were enriched in the inflammation, apoptosis, sugar transport, antioxidant, fructose, and mannose metabolism, arginine and proline metabolism, glycosaminoglycan biosynthesis, P53, and MAPK signaling pathways. This study offers new insight into the molecular mechanisms occurring in the lungs of M. mutica during acute hypoxia, which may facilitate genetic selection for hypoxia-resistant lines inM. mutica., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

The acclimation response of fish gills to chronic intermittent hypoxia (CIH) is an important aspect to understand, as anthropogenically induced hypoxia in water bodies has been a stressor for fish for many years and is expected to persist in the future. In order to investigate the acclimation response of fish gills to CIH stress, we conducted a study using largemouth bass (Micropterus salmoides) exposed to intermittent hypoxia (dissolved oxygen level, 2.0 mg·L -1 ) for either 1 or 3 h per day, over a period of 8 weeks. Our findings indicate that exposure to CIH induced remodeling of the gills and an increase in gill surface area. This remodeling of the gills may be attributed to changes in cell growth and proliferation, which are influenced by the activation of the MAPK signaling pathway. We also observed significant upregulation of genes related to glycolysis (fba, pgam1, pepck, atp-pfk, pfk-2, g6pi, gapd-1, and pk), while genes associated with cholesterol synthesis (3β-hsd, cyp51, dsdr- × 1, dsdr, and dhcr7) were downregulated following CIH exposure. Furthermore, we observed the presence of elongated megamitochondria in mitochondria-rich cells within the gills of fish exposed to hypoxia. Additionally, numerous genes involved in calcium signaling pathways were upregulated in the gills of largemouth bass, suggesting an enhanced sensitivity of gills to environmental cues in hypoxia conditions. However, the expression levels of certain genes related to innate and adaptive immune responses were inhibited following CIH exposure. Moreover, the number of mucous cells decreased after CIH exposure. This may have made the gills more susceptible to infection by pathogens, although it facilitated oxygen uptake. These findings highlight the potential vulnerability of gills to pathogenic organisms in the presence of CIH. Overall, our study contributes to a better understanding of how fish acclimate to CIH., Competing Interests: Declarations. Ethics approval: All experimental procedures and sample collection were approved by the Institutional Animal Care and Use Committee (IACUC) of the College of Animal Science and Technology of Sichuan Agricultural University, Sichuan, China, under permit No.2020302168. Competing interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)