Blood Respiratory Properties Research Articles

Implications of river damming: the influence of aquatic hypoxia on the diving physiology and behaviour of the endangered Mary River turtle

AbstractRiver impoundments are characterized by low oxygen levels as a result of reduced water velocity and increased water depth. Bimodally respiring turtle species are likely to be highly sensitive to changes in aquatic PO2 with decreases in oxygen levels impacting upon their diving ability. The acute and long‐term effects of aquatic hypoxia on dive duration, oxygen consumption and blood respiratory properties were examined in hatchlings of the endangered Mary River turtle Elusor macrurus. It was hypothesized that acute exposure to aquatic hypoxia would cause a decrease in dive duration as a consequence of a decrease in reliance on aquatic respiration. With long‐term exposure to hypoxia, we predicted that Elu. macrurus would have the capacity to compensate for the acute effect of hypoxia and that dive duration would increase due to an increase in aquatic respiration, haemoglobin concentration and oxygen affinity (P50). When exposed to hypoxic conditions, aquatic respiration in Elu. macrurus was substantially reduced resulting in a 51% decrease in dive duration. Contrary to our predictions, Elu. macrurus hatchlings did not acclimate, and long‐term exposure to hypoxic conditions caused Elu. macrurus to lose significantly more oxygen to the hypoxic water than the normoxic acclimated turtles. The exacerbation of long‐term hypoxia on the respiratory physiology and diving ecology of Elu. macrurus raises concerns about the impacts of long‐term environmental change as a result of habitat alteration on the survival of freshwater turtle populations.

Diving behaviour, aquatic respiration and blood respiratory properties: a comparison of hatchling and juvenile Australian turtles

AbstractAustralia has a number of bimodally respiring freshwater turtle species that use aquatic respiration to extend their aerobic dive limit. While species variations in reliance on aquatic respiration are reflected in the diving behaviour and ecology of adults, it is unknown whether these relationships also occur in hatchling and juvenile turtles. This study compared the diving behaviour, aquatic respiration and blood respiratory properties of hatchling and juveniles from five species of Australian freshwater turtles: Rheodytes leukops, Elusor macrurus, Elseya albagula, Elseya latisternum and Emydura signata. Both diving behaviour and physiology differed significantly between species as well as age classes. Dive duration in R. leukops was 17 times longer than the other species, with two hatchlings remaining submerged for the entire 72 h recording period. The long dive duration recorded for R. leukops was supported by a high reliance on aquatic respiration (63–73%) and high blood oxygen affinity (P50=17.24 mmHg). A correlation between dive duration, aquatic respiration and blood respiratory properties was not observed in the remaining turtle species where, despite the longer dive duration of Els. albagula and Elu. macrurus compared with Em. signata and Els. latisternum, there was no difference observed in per cent aquatic respiration or blood oxygen affinity between these species. When compared with adult individuals (data from previous studies), dive duration was positively correlated with body size in Em. signata, Els. albagula and R. leukops, but a negative relationship occurred in Els. latisternum and Elu. macrurus.

Thermal effects on the blood respiratory properties of southern bluefin tuna, Thunnus maccoyii

Thermal effects on the blood respiratory properties of southern bluefin tuna ( Thunnus maccoyii) at 10, 23 and 36 °C, and at 0.5 and 1.5% CO 2 were investigated. A reversed temperature effect occurred as the oxygen partial pressure required for 50% haemoglobin saturation ( P 50) at 0.5% CO 2 decreased from 2.9 kPa at 10 °C to 1.7 kPa at 23 °C (apparent heat of oxygenation, Δ H°, = + 27 kJ mol − 1 ). However, oxygen binding was essentially independent of temperature at warmer temperatures ( P 50 = 1.7–2.0 kPa from 23–36 °C at 0.5% CO 2; Δ H° = − 6.5 kJ mol − 1 ). Hill's coefficient ( n H) ranged from 1.3 to 1.6, and there was a large effect of temperature on the Bohr factor (Δlog P 50/ΔpH = − 1.6 at 10 °C and − 0.9 at 36 °C). This is the first study of whole blood to demonstrate the thermal dependence of Δ H° itself, whereby the oxygen equilibrium curve is more sensitive to temperature in the lowest thermal range examined. We suggest that the functional basis for these observations lies in the necessity to ensure a sufficient oxygen supply to all tissues, including the heart and liver, without suffering from premature or excessive oxygen unloading around the heat exchanger prior to delivery of oxygen to organs and tissues that lie efferent to the exchanger.

Respiratory properties of blood in flatback turtles (Natator depressus)

Oxygen equilibrium curves and other respiratory-related variables were determined on blood from the flatback turtle (Natator depressus) and, for comparison, on some samples from the loggerhead turtle (Caretta caretta). The oxygen carrying capacity of the flatback turtle, 4.9-8.7 mmol l(-1) (n = 49), is at the high end of the range in diving reptiles. Oxygen affinity (P(50)) was similar in both species at 5% CO(2), ranging from 37 to 55 mmHg (43 mmHg +/- 5.3 SD, n = 24, 25 degrees C, pH 7.17) in flatbacks and 43-49 mmHg in loggerheads (46 mmHg +/- 2.0 SD, n = 7, 25 degrees C, pH 7.13), whereas at 2% CO(2), flatbacks had a higher oxygen affinity. The curves differed in sigmoidicity, with Hill n coefficients of 2.8 and 1.9 in flatbacks and loggerheads, respectively. The Bohr effect was small in both the species, consistent with results from other sea turtles. Lactate levels were high, perhaps because the samples were taken from turtles coming ashore to lay eggs. Flatbacks are rarely found in waters deeper than 45 m. It is suggested that they have a respiratory physiology particularly suited to sustain prolonged shallow dives.

Temperature and the respiratory properties of whole blood in two reptiles, Pogona barbata and Emydura signata

We investigated the capacity of two reptiles, an agamid lizard Pogona barbata and a chelid turtle Emydura signata, to compensate for the effects of temperature by making changes in their whole blood respiratory properties. This was accomplished by measuring the P 50 (at 10, 20 and 30 °C), hematocrit (Hct), haemoglobin concentration ([Hb]) and mean cell haemoglobin concentration (MCHC) in field acclimatised and laboratory acclimated individuals. The acute effect of temperature on P 50 in P. barbata, expressed as heat of oxygenation (Δ H), ranged from − 16.8 ± 1.84 to − 28.5 ± 2.73 kJ/mole. P 50 of field acclimatised P. barbata increased significantly from early spring to summer at the test temperatures of 20°C (43.1 ± 1.2 to 48.8 ± 2.1 mmHg) and 30 °C (54.7 ± 1.2 to 65.2 ± 2.3 mmHg), but showed no acclimation under laboratory conditions. For E. signata, Δ H ranged from − 31.1 ± 6.32 to − 48.2 ± 3.59 kJ/mole. Field acclimatisation and laboratory acclimation of P 50 did not occur. However, in E. signata, there was a significant increase in [Hb] and MCHC from early spring to summer in turtles collected from the wild (1.0 ± 0.1 to 1.7 ± 0.2 mmol/L and 4.0 ± 0.3 to 6.7 ± 0.7 mmol/L, respectively).

Effect of ammonia on respiratory functions of blood of Tilapia zilli

The present paper attempts an examination of different changes of blood respiratory properties when Tilapia zilli is exposed to ammonia in three sublethal concentrations (1.1, 2.2 and 3.3 mg NH 3 l −1) for 2 weeks. The results revealed that oxygen and carbon dioxide partial pressures ( P O 2 and P CO 2 ) were changed differently and irregularly both in the caudal artery and in the heart. The acid–base status (pH, HCO − 3, TCO 2 and base excess) of arterial and venous blood changed towards alkalosis during the first week. These changes were exaggerated during the second week of ammonia exposure. O 2 saturation of arterial blood was decreased, while that of venous blood was increased due to the disturbances in blood gas transport and exchange mechanisms and in the acid–base status. The oxygen equilibrium curve was shifted to the left and P 50 was decreased during most of the experimental periods.

Isolated and combined exposure to ammonia and nitrite in rainbow trout (Oncorhynchus mykiss): effects on electrolyte status, blood respiratory properties and brain glutamine/glutamate concentrations

Rainbow trout (Oncorhynchus mykiss) were exposed for up to 4 days to 100, 300 and 500 μM ammonia and 0, 300 and 600 μM nitrite. Each ammonia concentration was combined with each nitrite concentration, giving a total of nine exposure groups. High mortality was observed in trout exposed to 500 μM ammonia in combination with 600 μM nitrite. Other exposure groups only showed sporadic mortality. Interactive effects (i.e. synergism or antagonism) of ammonia and nitrite exposure were not observed on the physiological parameters measured. Ammonia and nitrite, however, both caused a significant and additive decrease in muscle potassium concentrations after 4 days of exposure. The decrease was approximately 50 μmol g−1 dry weight for both nitrite and ammonia at the highest exposure concentrations. Nitrite was accumulated in plasma to approximately twice the ambient concentration, which was associated with a small significant increase in blood [lactate]. Plasma ammonia concentration only increased significantly upon ammonia exposure. The extracellular osmolality and Cl−, Na+ and amino acid concentrations remained constant. A transient increase in haematocrit and blood haemoglobin concentration was observed in trout exposed to the highest ammonia concentration. Accumulation of nitrite induced methaemoglobin formation and thereby functional anaemia, while no changes in red cell organic phosphates occurred. Plasma glutamate oxaloacetate transaminase (GOT) activity increased after 4 days exposure to the highest ammonia concentration. No changes occurred in plasma glutamate pyruvate transaminase (GPT) activity. Brain glutamate concentrations decreased while the brain glutamine concentrations increased in trout exposed to ammonia, suggesting detoxification of ammonia by its reaction with glutamate to form glutamine. Brain [glutamate] did not decrease below a threshold of approximately 2.37 μmol g−1 wet weight.

Air-Breathing Fishes: Evolution, Diversity, and Adaptation

The Biology of Air-Breathing Fishes: Introduction. Environmental Factors Affecting Air-Breathing Fishes. What is an Air-Breathing Fish? The Types of Air-Breathing Fishes. Summary and Overview. Diversity and Natural History: Introduction. The Class Osteicthyes: Families of Air-Breathing Fishes. Summary and Overview. Respiratory Organs: Introduction. Historical. Anatomy and Morphometrics. Types of Air-Breathing Organs. Lungs and Respiratory Gas Bladders. ABOs of the Higher Teleosts. Circulatory Adaptations: Introduction. Defining the Problems. Comparative Circulatory Specialization. Pulmonary Circulation: Lungfishes and Primitive Actinoperterygians. Summary and Overview. Aerial and Aquatic Gas Exchange: Introduction. Defining the Problems. Comparative Circulatory Specialization. Pulmonary Circulation: Lungfishes and Primitve Actinoperterygians. Summary and Overview. Cardiorespiratory Control: Introduction. Physical and Chemical Aspects. Comparative Aspects of Ventilatory Control: Fishes and Mammals. Studies of Bimodal Control. Studies of Central and Peripheral Control. Studies of ABO Receptors. Cardiorespiratory Reflexes. Summary and Overview. Blood Respiratory Properties: Introduction. Hemoglobin Function in Air-Breathing Fishes. Other Aspects of Air-Breathing Fish Blood Function. Summary and Overview. Metabolic Adaptations: Introduction. Oxygen Access and Intermediary Metabolism. Nitrogen Metabolism. Summary and Overview. Synthesis: Introduction. The Natural History of Fish Air Breathing. Factors Leading to the Evolution of Air Breathing. Air-Breathing Specializations. Air Breathing and Aquaculture. Fish Air Breathing and the Evolution of Tetrapods. References. Index.

Effects of Exhausting Exercise and Catecholamines on K + Balance, Acid-base Status and Blood Respiratory Properties in Carp

The potential role of adrenergic mechanisms in the recovery of potassium balance and acid-base status following 5 min of exhausting exercise was studied in carp. The extracellular metabolic H + load after exercise matched the lactate load, suggesting similar release rates of H + and lactate from white muscle. Blockage of α-adrenoceptors by phentolamine or β-adrenoceptors by propranolol neither influenced absolute magnitudes nor recovery kinetics of extracellular H + and lactate loads. The arterial oxygen tension increased following exercise, but blood oxygen transport was not improved via a red cell β-adrenergic response or modulation of the red cell nucleoside triphosphate content. Exercise induced an increase in extracellular [K +] which was corrected within 30–60 min of recovery. The recovery of K + balance was not influenced by blockage of adrenergic receptors. Red cell [K +] changed only insignificantly following exercise, whereby a possible function of the red cells as a temporary depository for K + during the extracellular hyperkalaemia could not be established. The minimal influence of catecholamines on the measured parameters during recovery from exercise was supported by an absence of change in these parameters upon adrenaline injection in resting carp.

Hemodynamics and Blood Properties of the Shortfin Mako Shark (Isurus oxyrinchus)

Lamnid sharks are difficult experimental subjects, and knowledge of their cardiovascular system has been largely based on morphological (Tota et al., 1983; Emery et al., 1985), histological (Sanchez-Quintana and Hurle, 1987; De Andres et al., 1990), biochemical (Farrell and Davie, 1991; Dickson et al., 1993), and hematological investigations (Wells and Davie, 1985; Emery, 1986). Because these sharks have a physiological capacity that exceeds other species (Graham et al., 1990), it is important to obtain cardiovascular data in living specimens. This report details in vivo studies of the cardiovascular and blood respiratory properties and the heartregulatory mechanism of shortfin mako sharks (Isurus oxyrinchus) carried out at sea on freshly collected specimens, most of which were subsequently released.

Effect of nitrite exposure on hematological parameters and blood respiratory properties in the sea bass Lates calcarifer

AbstractChanges in hematological parameters and blood respiratory properties of Lates calcarifer in response to nitrite exposure were studied. Exposure to 10 mg · L−1 NO2‐N for 8 days resulted in significant increases in blood nitrite and methemoglobin contents. Total hemoglobin was reduced resulting in an overall decline in functional hemoglobin. There was no significant change in hematocrit and red blood cell count.In another set of experiments, hematological parameters and venous blood oxygen tension of L. calcarifer after exposure to 15, 20, 30, 50, and 80 mg · L−1 NO2‐N for 4 days were determined. Blood nitrite and methemoglobin content increased proportionally to the increase in ambient nitrite concentration. The methemoglobin content (as percent of total hemoglobin) of fish immersed in a nitrite concentration equivalent to the 96 h LC50 (93 mg · L−1 NO2‐N) was estimated to be 83%. Venous blood oxygen tension tended to decrease as nitrite concentration increased.In a third set of experiments, sea bass were exposed to 50 mg · L−1 NO2‐N for 4 days. Exposure to nitrite resulted in lowered arterial and venous blood oxygen tensions, arterial and venous oxygen content, and blood oxygen capacity. However, no change in venous blood pH was observed between control and nitrite‐treated fish.The blood of Lates has a relatively low oxygen affinity (P50 = 14.5 ± 2.3 mm Hg) with a Hill coefficient (n) of 1.46. Exposure of fish to 50 mg · L−1 NO2‐N resulted in a leftward and upward shift of the blood oxygen dissociation curve (P50 = 5.9 ± 1.6 mm Hg; n = 0.99). The increased blood oxygen affinity in nitrite‐treated fish probably facilitated oxygen loading from water to the blood stream at the respiratory surfaces so as to compensate for the decline in oxygen carrying capacity. © by John Wiley & Sons, Inc.

Temperature acclimation of respiratory function in the salamander Taricha granulosa

The effect of acute and chronic temperature change on oxygen uptake (V̇ O 2 ) and the respiratory properties of blood was determined in the newt, Taricha granulosa. Acclimation to 20–24°C for 4 weeks caused a significant increase in hemoglobin concentration (6.5–9.5 g/dl) and O 2 capacity of blood but no change in oxygen affinity compared with animals acclimated to 4–6°C. Cold acclimated animals had a reverse Bohr effect compared with warm acclimated animals ( dlogP 50/dpH = +0.13 and −0.12 , respectively) but the present data offer no mechanism. There was no difference between the two acclimation groups with respect to temperature sensitivity of O 2 binding, cooperativity of binding, buffer capacity, red cell organic phosphate concentration, or red cell dimensions. There was no evidence for thermal acclimation of V̇ O 2 . Over the seasonal range of water temperature experienced by this species (5–25°C), the major adaptation to the ca. 4 fold increase in V̇ O 2 is a 49% increase in blood O 2 capacity.

Blood Respiratory Properties and the Effect of Swimming on Blood Gas Transport in the Leopard Shark Triakis Semifasciata

ABSTRACT Changes in vascular pressures, blood respiratory properties and blood gas transport induced by swimming were investigated in the leopard shark Triakis semifasciata (Girard). In resting sharks, the mean ventral and dorsal aortic pressures (systolic/diastolic) were 6.8/5.6 kPa and 4.5/3.9 kPa, respectively, and only the former were increased significantly during swimming. Swimming also caused a significant decline in venous , (1.6 to 0.9kPa), O2 content (0.9 to 0.4 mmol l−1) and percentage O2 saturation (, 39 to 18%) but the arterial variables were not affected. A significant decline in venous pH and an increase in venous also occurred during swimming but lactate concentration did not increase during or after swimming. An in vivo dissociation curve compiled from blood and data for sharks in the resting, swimming and post-swimming recovery phases shows a mean P50 of 2.04 kPa, as determined by Hill transformation. The pH-bicarbonate plot for this fish shows a weak blood buffer capacity of 9.3 mmol I−1 pH unit−1 and during swimming the average blood pH and bicarbonate concentration follow the buffer line which was not compensated in recovery. Neither oxygenated nor deoxygenated blood pH values were affected by CO2 equilibration, suggesting the absence of a Haldane effect. Thus, at the expense of respiratory acidosis, Triakis can aerobically sustain long (up to 60 min) and moderately intense (0.45 Ls−1, where L is body length) periods of swimming by increasing cardiac output and tapping its venous reserve.

Changes in blood respiratory properties and cardiovascular function during acute exposure to hypoxic water in an air‐breathing teleost, Channa maculata

Changes in blood respiratory properties and cardiovascular function of Channa maculata are described in fish acutely exposed to water of different oxygen tensions. The oxygen dissociation curve of the blood was hyperbolic, and the blood had a high oxygen affinity (P50= 7.6 mm Hg at pH = 7.6) and a large Bohr coefficient. The persistently higher blood oxygen level in the dorsal aorta compared with that in the bulbus arteriosus regardless of the ambient oxygen tensions tends to support Ishimatsu and Itazawa's (1983) suggestion that oxygenated and deoxygenated blood could be. at least partially, separated in the heart of Channa. Acute exposure to hypoxic water induced insignificant changes in blood oxygen tension and saturation. However, bradycardia, hypotension, haemodilution and antidiuresis were observed in fish exposed to severely hypoxic (PO2≤ 30 mmHg) but not to moderately hypoxic (PO2= 50 mmHg) water. These data suggested that Channa maculala possessed adaptive blood respiratory properties and blood circulation pattern to allow the fish to take up oxygen from air without significant branchial oxygen loss to the surrounding hypoxic water.

Respiratory Properties of Blood and Myoglobin in Hummingbirds

Blood respiratory properties were studied in several species of Brazilian hummingbirds. Three species, Melanotrochilus fuscus, Eupetomena macroura, and Amazilia versicolor, were studied with respect to O₂-Hb equilibrium curves and effect of pH and temperature. O₂ equilibrium of purified hemolyzates and myoglobin solutions from pectoral muscle were studied for Melanotrochilus fuscus. Hematocrit, hemoglobin content, and myoglobin concentration were studied for 11 species. Hematocrits averaged 56.3%; corresponding O₂ capacity was 22.1 vol%, and MCHC 27.0%. Average blood 02 affinity for the three species was 44.0 mmHg at pH 7.40 and 39 C. The Bohr coefficient ø was -0.39. The Hill plots were nonlinear and had increasing n-values at higher 02 saturations. The influence of temperature on the O₂-Hb equilibrium of whole blood was moderate, expressed by ΔH values of 7.0-8.0 Kcal mol⁻¹ The data are discussed with focus on the rapid changes in O₂ uptake and body temperature in hummingbirds associated with entry and arousal from torpor and the high O₂ uptakes of hovering flight. Hummingbird blood shows a very high unloading efficiency for 02. The increase in n-value at higher O₂ saturation is important because it prevents arterial desaturation during flight and nocturnal hypothermia.

Effects of nitrite exposure on blood respiratory properties, acid-base and electrolyte regulation in the carp (Cyprinus carpio).

Adult carp were subjected to 1 mM environmental nitrite for 48 h and nitrite uptake and changes in blood respiratory properties, extracellular electrolyte composition and acid-base status were examined. A constant influx of nitrite caused an accumulation of NO2- in plasma to 5.4 mM in 48 h. The fraction of methaemoglobin rose with plasma [NO2-] to 83%, and the arterial oxygen content decreased to extremely low values. Arterial PO2 increased as a compensation to this O2-shortage, whereas the O2 saturation of the functional (unoxidized) haemoglobin decreased, revealing a reduction in its O2 affinity. Blood haematocrit decreased as a result of red cell shrinkage, which caused very high red cell haemoglobin (Hb) concentrations. The erythrocytic nucleoside triphosphate (NTP) concentration showed a parallel increase whereby NTP/Hb, as well as the relative contributions of ATP and GTP to NTP, remained unchanged. Plasma [Cl-] declined by 15 mM in 48 h, offsetting the plasma [NO2-] increase, minor changes in plasma [HCO3-] and a considerable increase in plasma [lactate]. Arterial pH and [HCO3-] rose slightly during the first 24 h of nitrite exposure, but returned to control values at 48 h. The rise in plasma [lactate] was not reflected in an extracellular metabolic acidosis. Plasma [K+] increased by 94% in 48 h, revealing an uncompensated extracellular hyperkalemia, whereas plasma [Na+] decreased, and plasma [Ca++] was unchanged. Plasma osmolality remained essentially constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Influences of exercise-stress and adrenaline upon intra- and extracellular acid-base status, electrolyte composition and respiratory properties of blood in tench (Tinca tinca) at different seasons.

Exercise-stress in tench resulted in severe acidosis in both the red cells and the extracellular fluid in vivo. These coincident pH decreases conformed to the in vitro pHi-pHe relationship for tench blood in the oxygenated state. The extracellular acidosis was primarily respiratory in winter and metabolic in spring and summer. This was due to more effective buffering of metabolic protons in winter by an elevation in [HCO3-] levels, rather than to differences in the lactic- and carbonic acid loads. A good correspondence was found between buffered metabolic protons and increases in [lactate]. There was no evidence for beta-adrenergic red cell swelling and associated red cell pH changes in tench both after exercise and adrenaline infusion. Arterial O2 transport was, however, improved in exercise by pronounced increases in PO2. This increase was not of adrenergic origin, as adrenaline alone caused a decrease in arterial PO2. Large increases in plasma potassium concentration and small elevations of chloride and calcium levels occurred in exercise. Hematocrit and blood [Hb] also increased, probably due to an adrenergic release of erythrocytes from the spleen, but these increases were small and appeared unimportant for blood O2 transport. Seasonal differences were found in exercise-induced changes in [lactate], in the magnitude of electrolyte and PO2 changes, as well as in resting values for pHe, pHi, [HCO3-], [Cl-] and [Ca++]. The origin and importance of these are discussed.

Physiological consequences of prolonged aerial exposure in the American eel,Anguilla rostrata: blood respiratory and acid-base status

The physiological consequences of prolonged air-exposure on blood respiratory and acid-base properties were examined in the American eel (Anguilla rostrata). Eels displayed a low capacity for aerial gas transfer as indicated by pronounced increases and decreases in arterial CO2 and O2 tensions, respectively. The increase in arterial CO2 tension contributed to severe extracellular acidosis. The decrease in arterial O2 tension, combined with a marked reduction in red blood cell pH and concomitant Bohr and Root effects, caused arterial O2 content to decline to levels that were insufficient to support metabolic requirements, aerobically. Consequently, the rate of anaerobic glycolysis increased during air-exposure as suggested by a gradual elevation of blood lactate levels after 12 h. Increased anaerobic glycolysis and associated ATP hydrolysis and/or degradation of internal ATP stores further depressed blood pH as metabolic acid, produced by these processes, entered the circulation. Unlike other fishes previously examined, red blood cell pH was not regulated preferentially during the extracellular acidosis but simply conformed to the in vitro relationship between red blood cell and whole blood pH. Although capable of surviving prolonged air-exposure, the results demonstrate nevertheless and perhaps not surprisingly that eels, unlike true amphibious fishes that utilize gills or buccal epithelia for gas transfer, are not particularly well-adapted for gas exchange in air but do display an unusual tolerance to hypoxemia.

Blood respiratory properties in pigeons at high altitudes: effects of acclimation.

Many birds thrive at high altitudes where environmental temperatures are low. Previous studies have shown that tolerance of and acclimation to hypoxia involve cardiopulmonary and hematological adaptations. We investigated blood respiratory properties during exposure to simulated high altitude (hypobaric hypoxia) and low temperature in unanesthetized resting pigeons (Columbia livia, mean mass 0.38 kg). A control group (C) and a group acclimated to 7 km above sea level (ASL) in a hypobaric chamber at 25 degrees C (HA group) were used. All were acutely exposed to altitudes through 9 km ASL at 5 or 25 degrees C. Arterial and mixed venous blood gas tensions and O2 and CO2 content during steady state decreased with increased altitude, whereas blood lactate increased in both groups at both temperatures. Acute high-altitude exposure did not affect hematocrit, hemoglobin concentrations, or O2 carrying capacity, but at any altitude these were all greater in HA than in C birds. At 5 degrees C blood pH increased with altitude in controls but remained unchanged in HA birds. At 25 degrees C in both groups mean intracellular pH did not change, averaging 6.97, whereas extracellular (venous) pH increased with altitude. At the highest altitudes tissue O2 extraction was virtually complete in both groups. Acclimation changed blood O2 and CO2 combining properties in ways likely to improve gas transport at high altitudes. The previously unreported shifts in blood respiratory and acid-base properties with acclimation indicate that innate extrapulmonary adaptations contribute to avian hypoxia tolerance.

Oxygen transport, tissue glycogen stores, and tissue pyruvate kinase activity in muskrats

Oxygen stores, respiratory properties of blood, tissue glycogen concentrations, and the rate-limiting enzyme for glycolysis, pyruvate kinase, were examined in muskrats (Ondatra zibethicus). Of the potential oxygen stores, lung volume (19.6 ± 0.68 mL/kg), and blood hemoglobin concentration (13.0 ± 0.34 g Hb/100 mL blood) were typical of terrestrial mammals, while concentrations of myoglobin in heart (7.4 ± 0.1 mg Mb/g tissue) and gastrocnemius muscle (13.3 ± 0.5 mg Mb/g tissue) were significantly higher than values from the same tissues in the laboratory rat. Blood P50 (oxygen half-saturation pressure) at pH 7.4, 24.4 ± 1.36 Torr (1 Torr = 133.322 Pa), and Bohr effect, −0.64 ± 0.04, also were significantly different, while the Hill coefficient and buffering capacity were comparable for both species. Of our measures of anaerobic capacity, glycogen concentrations and pyruvate kinase activities in heart, brain, and gastrocnemius muscle of O. zibethicus were all comparable to values obtained for terrestrial mammals. We conclude that muskrats tolerate submersion by adaptations associated with aerobic metabolism, although a review of the literature shows that these adaptations are fully developed only in animals freshly captured during winter.