Comparative studies of the respiratory functions of mammalian blood. II. Marsupialia: great grey kangaroo and Tasmanian devil

Comparison of various approaches to calculating the optimal hematocrit in vertebrates

An interesting problem in hemorheology is to calculate that volume fraction of erythrocytes (hematocrit) that is optimal for transporting a maximum amount of oxygen. If the hematocrit is too low, too few erythrocytes are present to transport oxygen. If it is too high, the blood is very viscous and cannot flow quickly, so that oxygen supply to the tissues is again reduced. These considerations are very important, since oxygen transport is an important factor for physical performance. Here, we derive theoretical optimal values of hematocrit in vertebrates and collect, from the literature, experimentally observed values for 57 animal species. It is an interesting question whether optimal hematocrit theory allows one to calculate hematocrit values that are in agreement with the observed values in various vertebrate species. For this, we first briefly review previous approaches in that theory. Then we check which empirical or theoretically derived formulas describing the dependence of viscosity on concentration in a suspension lead to the best agreement between the theoretical and observed values. We consider both spatially homogeneous and heterogeneous distributions of erythrocytes in the blood and also possible extensions, like the influence of defective erythrocytes and cases where some substances are transported in the plasma. By discussing the results, we critically assess the power and limitations of optimal hematocrit theory. One of our goals is to provide a systematic overview of different approaches in optimal hematocrit theory.

Haemorheology of the eastern grey kangaroo and the Tasmanian devil

The blood of two Australian marsupials, the eastern grey kangaroo (Macropus giganteus) and the Tasmanian devil (Sarcophilus harrisii), has been reported to have greater oxygen-carrying capacity (i.e. haemoglobin content) when compared with that of placental mammals. We investigated whether alterations of blood rheological properties are associated with the increased oxygen-carrying capacity of these marsupials. Eastern grey kangaroos (n = 6) and Tasmanian devils (n = 4) were anaesthetised for blood sampling; human blood (n = 6) was also sampled for comparison. Laboratory measurements included blood and plasma viscosity, red blood cell (RBC) deformability, RBC aggregation and the intrinsic tendency of RBC to aggregate, RBC surface charge and haematological parameters. Scanning electron micrographs of RBC from each species provided morphological information. High-shear blood viscosity at native haematocrit was highest for the Tasmanian devil. When haematocrit was adjusted to 0.4 L L–1, lower-shear blood viscosity was highest for the eastern grey kangaroo. RBC deformability was greatly reduced for the Tasmanian devil. Eastern grey kangaroo blood had the highest RBC aggregation, whereas Tasmanian devil RBC did not aggregate. The surface charge of RBC for marsupials was ~15% lower than that of humans. The dependence of oxygen-delivery effectiveness on haemoglobin concentration (i.e. oxygen content) and blood viscosity was quantitated by calculating the haematocrit to blood viscosity ratio and was 15–25% lower for marsupials compared with humans. Our results suggest that environmental pressures since the marsupial–monotreme divergence have influenced the development of vastly different strategies to maintain a match between oxygen demand and delivery.

Oxygen affinity and 2,3-diphosphoglycerate in blood of Australian marsupials of differing body size

Oxygen carriage and 2,3-diphosphoglycerate (2,3-DPG) levels have been measured in the blood of seven species of Australian marsupials ranging in size from 35 to 0.03 kg. They were Red and Grey Kangaroos, Wallaroo, Tammar Wallaby, Brush-tailed possum, Potoroo, and Brown Marsupial Mouse. Oxygen affinity decreased with decrease in adult body size, standard P50 (at 36 C) varying from 24.6 torr in the largest (Red Kangaroo) to 41.9 torr in the smallest (Brown Marsupial Mouse). The relationship between P50 and body size is similar to the relationship which has been described previously for eutherian mammals. The Bohr factor (--deltalog P50/deltapH) and value for Hill n were generally in the range found for other land-dwelling mammals. All species had 2,3-DPG in their erythrocytes acting as a regulator of oxygen affinity. The polymorphism at position beta 2 in hemoglobin of the Grey Kangaroo was shown to affect the respiratory properties of the molecule. When beta 2 = histidine, which has a positively charged side chain, erythrocyte 2,3-DPG was higher, and P50 was higher, than when beta 2 = glutamine which has a neutral side chain.

Haematology and blood chemistry of the red kangaroo Megaleia rufa in captivity

Haematology and biochemistry was performed to establish base line values on not less than 30 samples of blood and serum from 10 red kangaroos Megaleia rufa held in captivity. The kangaroos were apparently healthy. Ranges for results were: Haemoglobin 16-18 gm/100 ml, PCV 46-51%, erythrocytes 4.9 - 5.7 times 10(6)/mm3. MCV 86-98 mum3, MCH 30-34 pg, MCHC 34-36%, leucocytes 3.8 - 7.1 times 10(3)/mm3, neutrophils 2.0 - 4.7 times 10(3)/mm3, lymphocytes 1.2 - 2.4 times 10(3)/mm3, monocytes 0.1 - 0.3 times 10(3)/mm3, eosinophils 0.06 - 0.013 times 10(3)/mm3, SGOT 36-43 u/l, SGPT 30-41 u/l, LDH 30-85 u/l, protein 6.0-6.8 g/100 ml, albumin 2.8 - 3.4 g/100 ml, alpha globulin 0.3 - 0.7 g/100 ml, beta globulin 0.7 - 0.9 g/100 ml, gamma globulin 1.7 - 2.3 g/100 ml, albumin/globulin 0.8 - 1.1, Na+ 146-152 mEq/l, K+ 4.6 - 5.6 mEq/l. Rectal temperature was 36.8 +/- 0.3. High haemoglobin may be characteristic of wild animals and of animals which have a high level of muscular activity and large erythrocytes may be representative of marsupials. Haematology as a tool of ecological investigation and its role in future research is briefly discussed. A modified staining technique for performing differential blood cell counts is described.