Assessment of the hemorheological profile of koala and echidna

Abstract

Koala, a marsupial, and echidna, a monotreme, are mammals native to Australia. Blood viscosity (62.5-1250s(-1)), red blood cell (RBC) deformability, RBC aggregation, aggregability and surface charge, and hematological parameters were measured in blood samples from six koalas and six echidnas and compared to adult human blood. Koala had the largest RBC mean cell volume (107.7+/-2.6fl) compared to echidna (81.3+/-2.6fl) and humans (88.4+/-1.2fl). Echidna blood exhibited the highest viscosity over the entire range of shear rates. Echidna RBC were significantly less deformable than koala RBC but more deformable than human RBC. Echidna RBC had significantly lower aggregability (i.e., aggregation in standardized dextran medium) than koala or human RBC, while aggregation in autologous plasma was similar for the three species. Erythrocyte surface charge as indexed by RBC electrophoretic mobility was similar for human and echidna cells but was 40% lower for koala RBC. Data obtained during this preliminary study indicate that koala and echidna have distinct hemorheological characteristics; investigation of these properties may reveal patterns relevant to specific behavioral and physiological features of these animals.

Fig. 1

Scanning electron micrographs of (A) koala, (B) echidna, and (C) human red blood cells. Original magnification of 3500 for each panel; horizontal white bar equal to 10 μm.

Fig. 2

Blood viscosity at (A) native hematocrit and (B) with hematocrit adjusted to 0.4 l/l for koala, echidna and human blood. N = 6 for each species. Data are mean ± standard error. Difference of human and echidna from koala: ** p < 0.01.

Fig. 3

Plasma viscosity for koala, echidna and human samples. N = 6 for each species. Data are mean ± standard error. Difference from echidna: ^† p < 0.05.

Fig. 4

Red blood cell elongation indexes measured at shear stresses between 0.5 and 20 Pa for koala, echidna and human RBC. N = 6 for each species. For clarity, elongation indexes measured at only seven representative shear stresses are presented. Data are mean ± standard error. Difference of human from echidna: ^† p < 0.05; ^†† p < 0.01. Difference of human from koala: ^** p < 0.01; ^*** p < 0.001. Difference of echidna from koala: ^‡‡ p < 0.01; ^‡‡‡ p < 0.001.

Fig. 5

(A) Shear stress for half-maximal deformation (SS_1/2) and (B) maximum EI at infinite shear stress (EI_max) for koala, echidna and human red blood cells. N = 6 for each species. Data are mean ± standard error. Difference from koala: ^** p < 0.01; ^*** p < 0.001. Difference from echidna: ^†† p < 0.01.

Fig. 6

Red blood cell aggregation indexes (M and M1) for koala, echidna and human measured in plasma (hematocrit = 0.4 l/l). N = 6 for each species. Data are mean ± standard error.

Fig. 7

Red blood cell aggregation indexes (M and M1) for (A) koala, (B) echidna and (C) human RBC suspended in plasma and three dextran solutions (hematocrit = 0.4 l/l). N = 6 for each species. Data are mean ± standard error. Difference from aggregation in plasma: * p < 0.05; ** p < 0.01; *** p < 0.001.

Fig. 8

Electrophoretic mobility of koala, echidna and human red blood cells. N = 6 for each species. Data are mean ± standard error. Difference from koala: ^*** p < 0.001. Difference from echidna: ^†† p < 0.01.