Blood oxygen transport and organ weights of two shrew species (S. etruscus and C. russula)

Abstract

Blood parameters concerning oxygen transport and relative organ weights of 11 Suncus etruscus and 13 Crocidura russula under light halothane anesthesia were investigated. Mean body weight of S. etruscus was 2.5 g and for C. russula was 9 g, hemoglobin concentration was 17.4 and 15.6 g/100 ml blood, hematocrit was 50 and 44%, red blood cells were 18 and 11 X 10(6)/microliter, respectively. Mean corpuscular volume was calculated to be 26 and 41 micron3, mean diameter 5.5 and 7 micron, and mean thickness 1.2 and 1.1 micron, respectively. Mean corpuscular hemoglobin concentration was in the normal range of mammalian red blood cells. A blood oxygen half-saturation pressure of 35 and 34 Torr at pH 7.4, 37 degrees C and a Bohr factor deltalog P50/deltapH of -0.61 and -0.66 was measured. Experiments with stripped hemoglobin showed that 2,3-diphosphoglycerate is the main oxygen affinity reducing allosteric factor. Relative weights of heart, kidney, and liver are remarkably high in S. etruscus. The maximal oxygen transport of 400 ml . kg-1 . min-1 of S. etruscus is feasible by an enormous heart rate, a large relative stroke volume, a high hemoglobin concentration combined with a low oxygen affinity, and a large Bohr effect.

Molecular and physicochemical characterization of hemoglobin from the high-altitude Taiwanese brown-toothed shrew (Episoriculus fumidus)

“…These authors further suggested that the high rate of proton generation at the tissues arising from this reaction, coupled with a relatively high Bohr factor, may allow the blood O 2 stores of small mammals to be more fully exploited. Consistent with these predictions, measured Bohr coefficients of shrew Hb and blood (-0.61 to -0.69) are at the upper range for mammals (Bartels et al 1979;Jürgens et al 1981; this study). However, our findings regarding the dual modulation of Episoriculus Hb by phosphate and chloride ions, together with its low thermal sensitivity and predicted low proton buffering capacity, suggest that the functional control of O 2 uptake and delivery in these diminutive insectivores may be more complex than previously suspected.…”

“…Under presumed intracellular conditions (pH 7.2 and 37°C) the P 50 of Episoriculus Hb devoid of anions (7.7 mmHg) is *75 % higher than that recorded for human HbA (4.4 mmHg; Perutz and Imai 1980) under the same conditions, and only half of that reported for 'stripped' hemolysates of S. etruscus and C. russula (13.1 and 17.4 mmHg respectively; Bartels et al 1979). Notably, however, these latter samples were eluted in 0.16 M Cl -Tris buffer (Jür-gens et al 1981) and thus are likely more comparable to values obtained from E. fumidus Hb in the presence of 0.1 M Cl -(14.8 mmHg; Table 1).…”

“…Hence, small homeothermic mammals must employ a suite of morphological and physiological adjustments to continually supply tissue mitochondria with sufficient O 2 to fuel oxidative metabolism. These include reduced diffusion distances, high circulatory and ventilatory gas transport capacities, and blood with relatively low affinity for O 2 (Bartels et al 1979;Gehr et al 1980;Morrison et al 1959). Moreover, the level of carbonic anhydrase (which catalyzes the hydration of CO 2 to HCO 3 -and H ? )…”

“…In this light, it is surprising that-apart from a single O 2 affinity measurement (oxygen half-saturation pressure or P 50 = 32.8 mmHg at 37°C, pH 6.8) of a dilute hemolysate solution from a short-tailed shrew, Blarina brevicauda (Foreman 1954)-no information appears to be available on the functional properties of the hemoglobin (Hb) of any red-toothed shrew. In fact, oxygen binding data are only currently available for hemolysates of two lowland species of crocidurine shrews (Etruscian shrew, Suncus etruscus and greater whitetoothed shrew, Crocidura russula) at pH 7.2 (Bartels et al 1979;Jürgens et al 1981). These studies suggest that a high Bohr factor (DLog P 50 /DpH = -0.61 to -0.66) coupled with a relatively low blood O 2 affinity (P 50 = *34-35 mmHg) integrally complements high ventilatory diffusion and circulatory transport capabilities to fuel the high aerobic metabolic rates of shrews.…”

“…cardiac output, respiration rate, blood oxygen carrying capacity) and morphological traits (i.e. mitochondrial capacity, diffusion distance, surface area for gas exchange) are presumably already operating at or near their upper limits (Bartels et al 1979;Gehr et al 1980;Morrison et al 1959), how (if at all) do the functional properties of the blood contribute to the adaptation of these species to high elevation?…”