Meeting Abstract
During dives, marine tetrapods experience physical changes in their surrounding environments, such as decreased temperature and increased pressure, which can introduce significant physiological challenges. Adipose tissue is of particular concern for diving physiology, because nitrogen gas is 5 times more soluble in fat than water/blood. Therefore, at any blood/tissue interface, gas will diffuse from blood into tissue, potentially forming gas bubbles upon decompression and increase the risk of decompression sickness. Exposure of tissues to N2 gas is a function of pressure, blood flow, and the number of blood vessels for exchange present. Interestingly, the degree of microvascularity (capillaries, microarterioles and microvenules) in the adipose tissue of diving tetrapods has not been studied. Percent microvascularity was determined by incubating frozen sections from four terrestrial mammals (Sus scrofa, Ovis aries, Capra aegagrus hircus, Bos taurus) and three diving tetrapods (Hippopotamus amphibius, Dermochelys coriacea, Somateria mollissima) in a solution of NBT/BCIP to stain for endogenous alkaline phosphatase. There is considerable variability in microvascular density across species. The percent microvascularity of terrestrial mammals was 0.81% (cow), 1.59% (pig), 5.38% (sheep), and 5.40% (goat). Comparatively, diving tetrapods had values of 2.03% (hippopotamus), 5.10% (eider duck) and 6.53% (leatherback turtle). The degree of microvascularity in diving tetrapods suggests the potential for gas exchange between blood and adipose at the microvessel level may be quite large.
