Assessment of the hemorheological profile of koala and echidna
Baskurt, OK, Marshall-Gradisnik, S, Pyne, M, Simmonds, M, Brenu, E, Christy, R & Meiselman, J 2010, Zoology, vol. 113, no. 2, pp. 110-117.
Blood samples from six echidnas and six koalas were analysed and compared to human blood for the following parameters: red blood cell (RBC) deformability, RBC aggregation, surface charge and aggregability, blood viscosity (62.5-1250 s -1) and hematological characteristics. The koalas had the highest average RBC volume (107.7 ± 2.6 fl) out of humans (88.4 ± 1.2 fl) and echidnas (81.3 ± 2.6 fl). RBC deformability of the koala was significantly greater than that of both human and echidna. RBCs of the echidna had less aggregability than human or koala RBCs, whilst aggregation was comparable for all three species in autologous plasma. RBC surface charge was similar between echidnas and humans, but 40% less in koalas by comparison.
Blood samples were withdrawn from the cephalic vein of six male koalas (Phascolarctos cinereus) and from two female and four male short-beaked echidnas (Tachyglossus aculeatus) through the beak sinus. All animals were determined to be healthy during sampling of blood. Blood samples from humans were taken from six male volunteers of healthy status. Measurements were performed by four hours post sampling. Platelet count, total hemoglobin and hematocrit did not vary significantly between groups. Koala RBCs presented significantly higher mean corpuscular hemoglobin and mean cell volume than both humans and echidnas, but mean corpuscular hemoglobin concentration in RBCs of koalas was less than in humans and greater than in echidnas. All species had RBCs that showed comparable sizes and shapes (roughly 8 mm and biconcave). Viscosity of koala blood was more similar to humans than echidnas in native hematocrit samples. Interestingly, koala RBCs presented the smallest electrophoretic mobility, being 50% less than values for humans and echidnas.
This study aimed to compare the hematological properties of monotremes, marsupials and mammals as they have not been extensively detailed in previous literature. These differences are a direct result of the diversification and adaptations of the three species to distinct environments. Echidnas’ have metabolic rates and body temperatures that are low and thus have a smaller cardiac output compared to mammals of the same size. Previous studies have indicated that koalas have respiratory and circulatory systems that are more similar to placental mammals than the echidna. In this study, viscosity measurements could only be taken at 37°C, but echidnas have body temperatures of 32°C, which likely affected blood viscosity readings. Higher viscosity is expected at lower temperatures, making measurements more similar to the other species. Using female echidnas may have also affected values. Low cytoplasmic viscosity and hemoglobin concentrations of the koalas may possibly explain differences in RBC deformability, but the mechanical behavior of cells must also be considered. Aggregability of RBCs may differ in species due to different surface charges and protein concentrations.
In conclusion, the findings from this paper show that hemorheological features between the species examined are similar even though they are evolutionarily distant. Such a narrow range in values is typically seen in species nearer in taxonomy, indicating that blood characteristics are a fundamental evolutionary feature. Future studies should analyse any present sex differences in hemorheological profiles.
Summarised by Alexander Murdoch
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