Comparative studies of the respiratory function of mammalian blood. V. Insectivora: shrew, mole and nonhibernating and hibernating hedgehog

The variable heartbeat of Japanese moles (Mogera spp.)

This report demonstrates the variable cardiac rhythm in two species of subterranean mole, the large Japanese mole (Mogera wogura) and the lesser Japanese mole (Mogera imaizumii). The phenomenon was revealed using X-ray videos of M. wogura and investigated in detail using electrocardiogram (ECG) traces recorded with implanted electrodes in this species and M. imaizumii. Cessation of heartbeat and extended R-R intervals were observed in the ECGs from both species during short bouts of rest in wakeful specimens of both species under normoxic conditions at room temperature. The mean durations of R-R intervals were 288.8 ± 3.3 ms for M. wogura and 191.9 ± 2.4 ms for M. imaizumii. The cardiac rhythm in both species became more unstable and R-R interval was prolonged by 153.5% ± 17.7 after injection of a sympathetic blocker (propranolol), whereas the application of a parasympathetic blocker (atropine) resulted in increasing stability and a reduced interval between R wave peaks (R-R) 64.2% ± 4.8. ECGs of two related soricomorphs, the fossorial Japanese shrew-mole (Urotrichus talpoides) and surface-dwelling Japanese white-toothed shrew (Crocidura dsinezumi) were also recorded and compared for comparison. The heartbeats of these species were relatively stable compared with those of the subterranean moles. Our results indicated clear differences in the physiological cardiac features between the examined members of the Soricomorpha.

Hibernation and gas exchange

Hibernation in endotherms and ectotherms is characterized by an energy-conserving metabolic depression due to low body temperatures and poorly understood temperature-independent mechanisms. Rates of gas exchange are correspondly reduced. In hibernating mammals, ventilation falls even more than metabolic rate leading to a relative respiratory acidosis that may contribute to metabolic depression. Breathing in some mammals becomes episodic and in some small mammals significant apneic gas exchange may occur by passive diffusion via airways or skin. In ectothermic vertebrates, extrapulmonary gas exchange predominates and in reptiles and amphibians hibernating underwater accounts for all gas exchange. In aerated water diffusive exchange permits amphibians and many species of turtles to remain fully aerobic, but hypoxic conditions can challenge many of these animals. Oxygen uptake into blood in both endotherms and ectotherms is enhanced by increased affinity of hemoglobin for O₂ at low temperature. Regulation of gas exchange in hibernating mammals is predominately linked to CO₂/pH, and in episodic breathers, control is principally directed at the duration of the apneic period. Control in submerged hibernating ectotherms is poorly understood, although skin-diffusing capacity may increase under hypoxic conditions. In aerated water blood pH of frogs and turtles either adheres to alphastat regulation (pH ∼8.0) or may even exhibit respiratory alkalosis. Arousal in hibernating mammals leads to restoration of euthermic temperature, metabolic rate, and gas exchange and occurs periodically even as ambient temperatures remain low, whereas body temperature, metabolic rate, and gas exchange of hibernating ectotherms are tightly linked to ambient temperature.

Decrease in the red cell cofactor 2,3-diphosphoglycerate increases hemoglobin oxygen affinity in the hibernating brown bear Ursus arctos

During winter hibernation, brown bears (Ursus arctos) reduce basal O(2) consumption rate to ∼25% compared with the active state, while body temperature decreases moderately (to ∼30°C), suggesting a temperature-independent component in their metabolic depression. To establish whether changes in O(2) consumption during hibernation correlate with changes in blood O(2) affinity, we took blood samples from the same six individuals of hibernating and nonhibernating free-ranging brown bears during winter and summer, respectively. A single hemoglobin (Hb) component was detected in all samples, indicating no switch in Hb synthesis. O(2) binding curves measured on red blood cell lysates at 30°C and 37°C showed a less temperature-sensitive O(2) affinity than in other vertebrates. Furthermore, hemolysates from hibernating bears consistently showed lower cooperativity and higher O(2) affinity than their summer counterparts, regardless of the temperature. We found that this increase in O(2) affinity was associated with a significant decrease in the red cell Hb-cofactor 2,3-diphosphoglycerate (DPG) during hibernation to approximately half of the summer value. Experiments performed on purified Hb, to which DPG had been added to match summer and winter levels, confirmed that the low DPG content was the cause of the left shift in the Hb-O(2) equilibrium curve during hibernation. Levels of plasma lactate indicated that glycolysis is not upregulated during hibernation and that metabolism is essentially aerobic. Calculations show that the increase in Hb-O(2) affinity and decrease in cooperativity resulting from decreased red cell DPG may be crucial in maintaining a fairly constant tissue oxygen tension during hibernation in vivo.

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.

Origin and mechanism of thermal insensitivity in mole hemoglobins: a test of the 'additional' chloride binding site hypothesis

The structural and evolutionary origins underlying the effect of temperature on the O(2) binding properties of mammalian hemoglobins (Hbs) are poorly understood, despite their potential physiological importance. Previous work has shown that the O(2) affinities of the blood of the coast mole (Scapanus orarius) and the eastern mole (Scalopus aquaticus) are significantly less sensitive to temperature changes than that of the star-nosed mole (Condylura cristata). It was suggested that this difference may arise from the binding of 'additional' chloride ions within a cationic pocket between residues 8His, 76Lys and 77Asn on the β-like δ-globin chains of coast and eastern mole Hbs. To test this hypothesis, we deduced the primary sequences of star-nosed mole and American shrew mole (Neurotrichus gibbsii) Hb, measured the sensitivity of these respiratory proteins to allosteric effector molecules and temperature, and calculated their overall oxygenation enthalpies (ΔH'). Here we show that the variability in ΔH' seen among mole Hbs cannot be attributed to differential Cl(-) binding at δ8, δ76 and δ77, as the Cl(-) sensitivity of mole Hbs is unaffected by amino acid changes at this site (i.e. the proposed 'additional' Cl- binding site is not operational in mole Hbs). Rather, we demonstrate that the numerically low ΔH' of coast and eastern mole Hbs results from heightened proton binding relative to other mole Hbs. Comparative sequence analysis and molecular modelling moreover suggest that this attribute evolved in a common ancestor of these two fossorial lineages and arises from the development of a salt bridge between a pair of amino acid residues (δ125His and α34Glu/Asp) that are not present in other mole Hbs.

Hedgehogs and sugar gliders: respiratory anatomy, physiology, and disease

This article discusses the respiratory anatomy, physiology, and disease of African pygmy hedgehogs (Atelerix albiventris) and sugar gliders (Petaurus breviceps), two species commonly seen in exotic animal practice. Where appropriate, information from closely related species is mentioned because cross-susceptibility is likely and because these additional species may also be encountered in practice. Other body systems and processes are discussed insofar as they relate to or affect respiratory function. Although some topics, such as special senses, hibernation, or vocalization, may seem out of place, in each case the information relates back to respiration in some important way.

Structure of the altitude adapted hemoglobin of guinea pig in the R2-state

BACKGROUND

Guinea pigs are considered to be genetically adapted to a high altitude environment based on the consistent finding of a high oxygen affinity of their blood.

METHODOLOGY/PRINCIPAL FINDINGS

The crystal structure of guinea pig hemoglobin at 1.8 A resolution suggests that the increased oxygen affinity of guinea pig hemoglobin can be explained by two factors, namely a decreased stability of the T-state and an increased stability of the R2-state. The destabilization of the T-state can be related to the substitution of a highly conserved proline (P44) to histidine (H44) in the alpha-subunit, which causes a steric hindrance with H97 of the beta-subunit in the switch region. The stabilization of the R2-state is caused by two additional salt bridges at the beta1/beta2 interface.

CONCLUSIONS/SIGNIFICANCE

Both factors together are supposed to serve to shift the equilibrium between the conformational states towards the high affinity relaxed states resulting in an increased oxygen affinity.

Molecular basis of a novel adaptation to hypoxic-hypercapnia in a strictly fossorial mole

Background

Elevated blood O₂ affinity enhances survival at low O₂ pressures, and is perhaps the best known and most broadly accepted evolutionary adjustment of terrestrial vertebrates to environmental hypoxia. This phenotype arises by increasing the intrinsic O₂ affinity of the hemoglobin (Hb) molecule, by decreasing the intracellular concentration of allosteric effectors (e.g., 2,3-diphosphoglycerate; DPG), or by suppressing the sensitivity of Hb to these physiological cofactors.

Results

Here we report that strictly fossorial eastern moles (Scalopus aquaticus) have evolved a low O₂ affinity, DPG-insensitive Hb - contrary to expectations for a mammalian species that is adapted to the chronic hypoxia and hypercapnia of subterranean burrow systems. Molecular modelling indicates that this functional shift is principally attributable to a single charge altering amino acid substitution in the β-type δ-globin chain (δ136Gly→Glu) of this species that perturbs electrostatic interactions between the dimer subunits via formation of an intra-chain salt-bridge with δ82Lys. However, this replacement also abolishes key binding sites for the red blood cell effectors Cl^-, lactate and DPG (the latter of which is virtually absent from the red cells of this species) at δ82Lys, thereby markedly reducing competition for carbamate formation (CO₂ binding) at the δ-chain N-termini.

Conclusions

We propose this Hb phenotype illustrates a novel mechanism for adaptively elevating the CO₂ carrying capacity of eastern mole blood during burst tunnelling activities associated with subterranean habitation.

In vivo blood oxygen binding in hypoxic lesser spear-nosed bats: relationship to control of breathing

The hypoxic ventilatory threshold of many mammals correlates with their hemoglobin-oxygen affinity (P50). Yet, in some small mammals ventilation actually declines, rather than increases, with exposure to decreasing PaO2; their air convection requirement (V(E)/V(O2)), however, is elevated in hypoxia. We propose that the threshold of the hypoxic V(E)/V(O2) of small mammals coincides with the inflection ('knee') of their in vivo O2 equilibrium curve (O2EC). In vivo blood gas and pH data were obtained from normoxic and hypoxic lesser-spear nosed bats, Phyllostomus discolor; in vitro blood O2EC were also generated for normoxic bats at 32 and 37 degrees C and at three P(CO2)'s. The hypoxic V(E)/V(O2) threshold of P. discolor occurs at PaO2 = 39 Torr; the corresponding in vivo O2 saturation is 0.70, approximating the inflection of the O2EC. This animal has a high blood O2 affinity (P50 = 27.5 Torr at pH 7.40 and 37 degrees C; P50 = 30.8 Torr at in vivo pH of 7.31 and TB of 37.4 degrees C). As PaO2 is reduced, a pronounced hypoxia-induced respiratory alkalosis and hypothermia help maintain SaO2 near the O2EC inflection (0.64-0.70 S(O2)).

Effects of hibernation on blood oxygen transport in the golden-mantled ground squirrel

Isocapnic O2 equilibrium curves (O2EC) were generated for winter hibernating and summer active ground squirrels (Spermophilus lateralis) at 7 degrees and 37 degrees C using thin blood film techniques. Half-saturation PO2 at 7 degrees C and pHa 7.46 were 5.8 +/- 0.1 and 6.9 +/- 0.2 Torr for hibernating and summer squirrels, respectively; P50 values at 37 degrees C and pHa 7.49 were 15.3 +/- 0.1 and 18.1 +/- 0.5 Torr, respectively. This increased blood O2 affinity in the winter animal results, in part, from reductions of RBC organic phosphates. The molar ratio ([ATP] + [DPG])/[Hb4] decreased from 1.55 in summer squirrels to 0.91 in winter hibernators. O2EC shape and CO2 Bohr effect were similar for the two animal groups, but varied with blood temperature. At 7 degrees C, Hill plots were nonlinear; Hill's n increased from values of 2.2-2.4 below 40% S to 2.7-2.9 above 60% S. At 37 degrees C, Hill plots were reasonably linear (n = 2.5). CO2 Bohr slopes (delta log P50/delta pH) for hibernating and euthermic squirrels were -0.37 +/- 0.02 and -0.40 +/- 0.03 at 7 degrees C, respectively, and -0.62 +/- 0.04 and -0.60 +/- 0.02 at 37 degrees C, respectively. Blood O2 capacity was significantly greater (P < 0.001) in the hibernator; hematocrit (55%) and [Hb] (19.1 g/dl) exceeded the summer squirrel values by 20% and 25%, respectively. Estimated PvO2 values for summer and winter animals at 7 degrees C and pH 7.46 were 7.25 and 6.94 Torr, respectively. This suggests that the effect of increased Hb-O2 affinity on PvO2 is offset by increased circulating [Hb]. We conclude that seasonal changes in the O2 transport properties of squirrel blood do not contribute to the depression of aerobic metabolism during winter hibernation.

Oxygen binding functions of blood and hemoglobin from the Chinese pangolin, Manis pentadactyla: possible implications of burrowing and low body temperature

We measured O2 equilibria of adult blood and of 'stripped' (cofactor-free) hemolysates from adult and newborn Manis pentadactyla, in order to assess the implications of the burrowing habit and the low deep-core temperature in pangolins, and to discern the mechanisms for maternal-fetal O2 transfer. At pH 7.4 and body temperature (33 degrees C) the blood O2 affinity was significantly higher than in similarly sized non-burrowing, 'normothermic' mammals (P50 = 21 and 33 mm Hg, respectively) indicating an adaptation to hypoxic burrow conditions. This difference is not attributable to a higher intrinsic O2 affinity in the pangolin Hb or to significant differences in its sensitivity to temperature and erythrocytic 2,3 diphosphoglycerate (DPG), but tallies with lower DPG/Hb ratios than generally found in mammals. Stripped adult and newborn hemolysates show similar O2 affinities and pH and DPG sensitivities, but reveal a specific adult Hb that develops after birth, in sharp contrast with the ontogenetic changes in other mammals where specific fetal Hbs are lost after birth.

Adaptation of hemoglobin function to subterranean life in the mole, Talpa europaea

In order to understand the mechanism responsible for the high oxygen affinity of mole blood, we investigated in the mole. Talpa europaea, red cell parameters that determine hemoglobin function. We have found that the oxygen half saturation pressure (P50) of mole blood is 2.85 kPa (21.4 Torr) at pCO2 4.7 kPa, pH 7.4 and 37 degree C. The concentration of 2,3-diphosphoglycerate (2,3-DPG) averaged 5.3 mmol/l in red cells. In addition, we have determined P50 in hemoglobin solutions at various concentrations of 2,3-DPG at an assumed intraerythrocytic pH of 7.2 and 37 degree C. These data were used to calculate the association constants of 2,3-DPG to mole hemoglobin. P50 was 1,89 kPa (14.2 Torr) in hemoglobin solutions without 2,3-DPG. The response to 2,3-DPG was relatively low. Noteworthy, CO2 did not affect the oxygen affinity at constant pH in the presence of 2,3-DPG. Our results suggest that the high blood oxygen affinity of the mole can be attributed to a weak interaction of its hemoglobin with 2,3-DPG.

Scaling of oxidative and glycolytic enzymes in mammals

The catalytic activities of several oxidative and glycolytic enzymes were determined in the gastrocnemius muscle of 10 mammalian species differing in body weight by nearly 6 orders of magnitude. When expressed in terms of units gm-1, the activities of enzymes functioning in oxidative metabolism (citrate synthase, beta-hydroxybutyrylCoA dehydrogenase, and malate dehydrogenase) decrease as body weight increases. Log-log plots (activity gm-1 vs body mass) yield straight lines with negative slopes that are less than the allometric exponent (-0.25) typically observed for basal metabolic rates. Since the amount of power a muscle can generate depends upon the catalytic potential of its enzyme machinery (the higher the catalytic potential the higher the maximum rate of energy generation), these data predict that the scope for aerobic activity in large mammals should be greater than in small mammals if nothing else becomes limiting, a result in fact recently obtained by Taylor et al. (Respir. Physiol., 1981). In contrast to the scaling of oxidative enzymes, the activities of enzymes functioning in anaerobic glycogenolysis (glycogen phosphorylase, pyruvate kinase, and lactate dehydrogenase) increase as body size increases. Log-log plots (activity gm-1 vs body mass) display a positive slope indicating that the larger the animal the higher the glycolytic potential of its skeletal muscles. This unexpected result may indicate higher relative power costs for burst type locomotion in larger mammals, which is in fact observed in within-species studies of man. However, the scaling of anaerobic muscle power has not been closely assessed in between-species comparisons of mammals varying greatly in body size.

Respiratory properties of whole blood and hemoglobin from the burrowing reptile, Amphisbaena alba

Respiratory properties of whole blood and hemoglobin solutions have been studied in the burrowing reptile, Amphisbaena alba. Whole blood is distinguished from that of other squamate reptiles by an extraordinary high O2 affinity (P50 = 12 mmHg at pH 7.60 and 25 degrees C). The Bohr factor, phi, was large at -0.85 and the n-value was 1.80. O2 capacity averaged 12.0 vol%. The molar concentration of erythrocyte ATP was high and twice that of hemoglobin. Stripped Amphisbaena hemoglobin shows an extremely high O2 affinity and reduced pH sensitivity compared to whole blood (P50 = 1 mmHg at pH 7.60 and 25 degrees C, phi = -0.35, n-value = 2.0). The hemoglobin O2 affinity was much more sensitive to ATP than for other poikilotherm vertebrates. Isoelectric focusing revealed a multicomponent hemoglobin with the major components showing similar O2 affinities and Bohr shifts. The data obtained are discussed in relation to the burrowing habits of Amphisbaena and found to be adaptive to a fossorial mode of life.

Metabolic, respiratory and haematological adjustments of the little pocket mouse to circadian torpor cycles

Metabolic, respiratory and haematological parameters were investigated for the Little Pocket mouse during circadian torpor cycles. The rate of O2 consumption decreased from 7.04 to 0.05 ml O2.g-1.hr-1, with a corresponding decrease in respiratory minute volume from 49.4 to 0.9 ml.min-1 during torpor at an ambient temperature of 10 C. No changes in haemoglobin concentration (19.7 g/100 ml), haematocrit (54%), red blood corpuscle count (12.4 10(6)/microliter), mean corpuscular volume (43.6 micrometer3), mean corpuscular haemoglobin content (16.2 pg), mean corpuscular haemoglobin concentration (37.4%) and [2,3-DPG] (9.6 mumol/g Hb) were observed during torpor cycles. The half saturation tension of P. longimembris haemoglobin was 41 mm Hg (37 C, pH = 7.28) and 19.7 mm Hg (10 degrees C, pH = 7.51). The effect of temperature on P50 was deltalog P50/ C = +0.0106 (pH = 7.4). Venous blood parameters were: euthermic mice (37 C); PCO2 = 36.8 mm Hg, PO2 = 49.5 mm Hg, pH = 7.28, [HCO-3] = 17.3 mmol/l; torpid mice (10 C); PCO2 = 14.6, PO2 = 35.7 pH = 7.51, [HCO-3] = 18.8. These data indicate a new, relatively acidotic acid-base status during torpor, characterised by a higher H+/ OH- ratio. The respiratory sensitivity to inspired CO2 of pocket mice was, despite their being semi-fossorial, typical of other mammals. High concentrations of CO2 did not induce, or facilitate, entry into torpor.

The phylogenetic distribution of red cell 2,3 diphosphoglycerate and its interaction with mammalian hemoglobins

In order to better understand the extent to which 2,3 diphosphoglycerate (DPG) contributes to red cell function in the mammals, we assayed DPG levels in blood from a taxonomically diverse set of 71 species representing 14 orders. In addition, for 66 species and 4 hemoglobin phenotypes of the sheep, the effect of DPG on oxygen affinity was measured by determining P 50 values for hemoglobin in the absence of DPG and at 0.2 mM and 1.0 mM concentrations. Most mammals had high levels of red cell DPG and phosphate-free hemoglobins with a relatively high oxygen affinity. In contrast, two taxonomically unrelated groups had both very low intra-erythrocytic DPG concentrations as well as hemoglobins of native low oxygen affinity that interacted weakly with DPG. This latter group includes the Feloidea (order Carnivora) and the Bovoidea (order Artiodactyla). The relationship between DPG concentration, hemoglobin oxygen affinity and the interaction of DPG with hemoglobin is treated quantitatively to provide a model of mammalian red cell function. This derived expression is compared with descriptive allometric equations for whole blood P 50 and is shown to provide statistically reasonable predictions.

Blood-gas properties and function in the fossorial mole rat under normal and hypoxic-hypercapnic atmospheric conditions

Blood and tissue gas exchange properties of mole rats in normoxic and hypoxic-hypercapnic conditions were compared to the common mammalian pattern. RBC count was 14.0 +/- 1.2-10(6)/microliter. Hb concentration was 15.0 +/- 0.4g/100 ml. P50 (at pH 7.4 and 37 degrees C) was 29.5 +/- 0.5 mm Hg. Oxygen capacity averaged 20.2 +/- 0.4 vol% and the Hill coefficient was 2.9 +/- 0.1. The Bohr effect was -0.53 +/- 0.02 (deltalog P/deltapH). The temperature coefficient was 0.0152 +/- 0.0014 (deltalog P/delta degrees C). The Haldane effect was 4.8 +/- 0.5 (deltaCCO2 vol%)at PCO2 =40 mm Hg. Steady-state partial pressures in gas pockets were PO2 = 15.1 +/- 1.4 mm Hg and PCO2 = 85.8 +/- 3.9 mm Hg in normoxia, and 11.5 +/- 3.0 and 101.8 +/- 3.5 repectively in hypoxia-hypercapnia (PIO2 congruent to 85 mm Hg). Under the same conditions 2,3-DPG dropped from 0.87 and 0.88 to 0.62 and 0.65 (mol/mol Hb) in the rat and in the white rat, respectively. Heart muscle myoglobin concentration of the mole rat (1.44 mg/g) did not differ significantly from that of the white rat (1.96 mg/g), whereas masseter myoglobin was 4.0 mg/g--significantly different from the rat (1.21 mg/g). Results indicate that the strategy used by the mole rat to maintain a normal metabolic rate under variable atmospheric conditions, besides having high oxygen affinity, is to expand the physiological range of the oxygen dissociation curve to very low oxygen tensions, at the expense of its acid-base regulation. The regulation of the shape of the oxygen dissociation curve is discussed.

Blood respiratory properties in the naked mole rat Heterocephalus glaber, a mammal of low body temperature

Respiratory properties of whole blood and Hb solutions have been studied in Heterocephalus glaber, a fossorial rodent, having a low body temperature (30.0-32.0 degrees C) and poor thermoregulatory ability. For comparison similar, measurements were made on laboratory mice, Mus musculus. Whole blood showed a distinctly higher O2 affinity for Heterocephalus at both 30 and 37 degrees C.P50 values were 23.3 mm Hg and 33.0 mm Hg at 37 degrees C for Heterocephalus and Mus, respectively, while at 30 degrees CP50's were 18.8 mm Hg and 24.9 mm Hg, all values at pH (b) 7.4. deltaH values (expressive of the effect of temperature on P50) were -5.8 kcal-mol-1 for Heterocephalus and -7.5 kcal-mol-1 for Mus. The CO2 Bohr effects (omega) were -0.43 and -0.50 for Heterocephalus at 37 and 30 degrees C. Corresponding values for Mus were -0.65 and -0.56. Both species had a Hill's n-value of 2.6. Red cell concentrations of 2,3-DGP were closely similar in the species being 7.3 mmol-L-1 rbc for Heterocephalus and 7.4 mmol-L-1 rbc for Mus. Stripped Heterocephalus Hb had a very high O2 affinity, at pH 7.25, 37 degrees C,P50 was 8.0 mm Hg whereas the corresponding value for Mus was 11.3 mm Hg. Addition of DPG to stripped Hb from the two species decreased O2 affinity to the same degree. The high O2 affinity of Heterocephalus blood is viewed as a possible adaptation to its burrowing habits. Its basis is inherent to the hemoglobin molecule itself and not dependent upon cofactor influence or the temperature sensitivity of the O2-Hb binding.

Respiratory function of blood in hibernating and non-hibernating hedgehogs

The oxygen affinity of the blood of hibernating hedgehogs has been investigated previously by Clausen and Ersland (1968) and Bartels et al. (1969). The results of these studies were conflicting in so far as Bartels et al. (1969) found an increase of the O2 affinity during hibernation resulting in a P50 of 23 mm Hg at pH 7.4 37 degrees C, while Clausen and Ersland reported a P50 of 33.6 mm Hg under the same conditions, a value which was only slightly different from the one found in nonhibernating animals (Bartels et al., 1969).