Oxygenating blubber: a challenge for fat animals

Large fat depots are associated comorbidities in humans. Biomedical studies show that tissue expansion leads to structural tissue modifications and potential hypoxia as result of low vascularity or impaired diffusion due to large adipocyte size. How blubber maintains adequate oxygenation and readjust tissue structure is unknown. Here, we examine blubber depth and fatness effects on tissue oxygenation and blubber characteristics. Blubber dissolved oxygen levels (pO₂) were measured in dorsal flank blubber on juvenile grey seals (n=10) under appropriate sedation and anaesthesia. Measurements were taken at different blubber depths, with an optical, non-consuming oxygen probe. Oxygen supply was investigated recording systemic blood saturation (SpO₂), breathing rate and oxy-haemoglobin and deoxygenated haemoglobin. The later was measured using a novel non-invasive technique: Near Infrared Spectroscopy (NIRS). Body composition and heart rate were also recorded. To examine vascularity and tissue structure changes throughout depth and fatness, full blubber depth biopsies of mother and pup pairs were taken at early and late lactation (n = 6). Biopsies were fixed in formalin, processed and stained with Masson’s Trichrome. Each biopsy was divided into three sections, and five images of each section were analysed by Image J. In vivo oxygen measurements ranged between 11 mmHg and 59 mmHg (mean = 32 mmHg), consistent with levels on other species. Linear mixed effect analysis (LMM) showed that tissue oxygenation had a significant positive relation with SpO₂ (p-value = 0.04) and a negative relationship with depth section (p-value Inner vs Outer = 0.02; p-value Inner vs Middle = 0.17; p-value Outer vs Middle = 0.46) and fatness (p-value = 0.04), independently of the individual (R²_marginal = 0.59, R²_conditional = 0.59). Results show that tissue expansion is also a challenge for seals. NIRS and histology data analysis are underway to explore oxygen supply, vascularity and tissue structure role on oxygenation.