Oxygen dissociation curves in trained and untrained subjects

Summary Oxygen dissociation curves (ODC) in whole blood and organic phosphate concentrations in red cells were determined in 10 highly trained male athletes (TR), 6 semitrained subjects (ST) who played sports regularly at low intensities and 8 untrained people (UT). In all groups standard ODCs (37 C, pH 7.40, Pco₂43 Torr) at rest and after a short exhaustive exercise were nearly identical, but P _o2 values measured immediately after blood sampling and corrected to standard conditions tended to fall to the right of the in vitro ODC. Elevated P₅₀ in the physically active [28.6±1.4 Torr (3.81±0.18 kPa) in ST, 28.0±1.1 Torr (3.73±0.15 kPa) in TR, but 26.5±1.1 Torr (3.53±0.15 kPa) in UT] were partly caused by different [DPG] (11.9±1.3 mol/gHb in UT, 13.3±1.5 mol/gHb in TR, 13.8±2.2 mol/gHb in ST). There were remarkable differences in the shape of the curves between the groups. The slope n in the Hill plot amounted to 2.65±0.12 in UT, 2.74±0.12 in ST and 2.90±0.11 in the TR (2 p against UT<0.001), leading to an elevated oxygen pressure of about 2 Torr (0.27 kPa) at 20% saturation and an augmented oxygen extraction of 5–7 So₂ at a Po₂ of about 15 Torr (2 kPa), which might be favorable at high workloads.The reason for the phenomenon could be an increased amount of young red cells in the blood of TR, caused by exercise induced hemolysis.A preliminary report was presented at the 49th Meeting of the German Physiological Society [Pflügers Arch. (Suppl.), 373, R 57 (1978)]     

Effects of inositol hexaphosphate on the Bohr effect induced by CO2 and fixed acids in chicken hemoglobin

Bohr factors, = logP _{O 2}/ pH, were measured in chicken hemoglobin (Hb) solutions at various levels of O₂ saturation in the absence and the presence of inositol hexaphosphate (IHP). pH changes were induced either by changingP _{CO 2}at constant base excess near zero (CO₂ Bohr factor, {ie135-1}) or by addition of fixed acid or base at constantP _{CO 2}(fixed acid Bohr factor, {ie135-2}). In the presence of IHP in a concentration of about 1.2 mol per mol Hb tetramer the two Bohr factors did not differ, the mean value being –0.61 (pH range, 7.1 to 7.6), independent of O₂ saturation (S _{O 2}) between 10 and 90%. Removal of IHP significantly decreased {ie135-3} to –0.25) pH range, 7.0 to 7.6), independent ofS _{O 2}, whereas the reduction in {ie135-4} was much less pronounced. Thus {ie135-5}, which showed a decrease with increasingS _{O 2}, exceeded {ie135-6} at all levels ofS _{O 2}. The data show that chicken hemoglobin is capable of binding CO₂ as oxygen-linked carbamate. But, at about equimolar concentrations of IHP and the tetrameric hemoglobin, oxylabile carbamate formation is abolished. It is suggested that this interaction between CO₂ and the organic phosphate compound accounts for the lack of a difference between the two Bohr factors in avian whole blood (cf. Meyer et al., 1978) where inositol pentaphosphate is present at about the same concentration as tetrameric hemoglobin.     

Fixed acid and carbon dioxide bohr effects as functions of hemoglobin-oxygen saturation and erythrocyte pH in the blood of the frog,Rana temporaria

Using a thin film, dynamic recording technique, the pH sensitivity of the oxygen equilibrium (Bohr effect) of whole blood in the frogRana temporaria, and its dependence on CO₂ and fixed acids and on plasma and erythrocyte pH values were measured. Under standard conditions (20°C,P _{CO 2}=14.7 mm Hg, pH=7.65) the oxygen equilibrium could be described by a P₅₀ value of 38 mm Hg andn ₅₀ of 1.8. Hill plots of the oxygen equilibria showed increased cooperativity in oxygen binding with increasing saturation (n ₂₀ 1.2,n ₈₀ 4.0). Values of the fixed acid and CO₂ Bohr factors ({ie7-1} and {ie7-2}, respectively) were similar at specific saturations (S_{20, 50, 80}) but showed saturation dependence with high values occurring at high saturation. The same statements also hold for the intracellular Bohr factors (derived from the relation between blood P₅₀ and erythrocyte pH) although the values of both {ie7-3} and {ie7-4} now were greater than those related to blood pH.     

Influence of fiber,xylitol and fructose in enteral formulas on glucose and lipid metabolism in normal subjects

Summary To verify the benofit of nonglucose carbohydrates and fiber in enteral formula diets we studied the postprandial metabolism of eight healthy subjects after the intake of two helpings (25 g carbohydrates each) of five commonly used enteral formulas over 4 h. There were no significant differences in postprandial concentrations of blood glucose among the formulas. The area under the curve of postprandial insulin values, however, was significantly smaller after consumption of the fructose-containing formula (1948±285 U min ml^–1, P<0.05) than after fiber-free (3222 ±678 U min ml^–1) or two fiber-containing products (2664±326 U min ml^–1, P<0.05; and 3040±708 U min ml^–1, P<0.05). The insulin area of the xylitol-containing formula (2307±364 U min ml^–1) was significantly smaller compared to the fiber-free product (P<0.05). In addition, we found the postprandial increase in triglycerides to be significantly higher after the xylitol-containing formula (from 0.93±0.14 to 1.25±0.22 mmol/1) than after the fiber-free product (from 0.82±0.13 to 0.97±0.16 mmol/1, P<0.05) or the two fiber-containing products (from 0.88±0.16 to 0.96±0.18 mmol/1, P<0.05; and from 0.80±0.08 to 0.95±0.10 mmol/l, P<0.05). We conclude that a patient with type 11 diabetes may benefit from replacing glucose and glucose-equivalent carbohydrates with fructose or xylitol.Abbreviation IAB area under curve of current insulin values minus baseline insulin values     

Effect of an increase in{\text{Hb}}_{{\text{O}}_{\text{2}} } affinity on the calculated capillary recruitment of an isolated rat heart

The effect of an increase in hemoglobin O₂ affinity on myocardial O₂ delivery was studied in a blood perfused working rat heart preparation. In a first series of experiments P₅₀ ( for which saturation is 50%) was lowered by use of carbon monoxide. The heart was alternatively perfused with the blood sample of P₅₀=32 mm Hg and the blood sample of P₅₀=17 mm Hg. O₂ capacity of both samples was kept the same by appropriate hemodilution. In a second serie of experiments change of P₅₀ was obtained by the use of adult human erythrocytes containing hemoglobin creteil with a P₅₀ of 13.6 mm Hg. As P₅₀ decreased from 25 to 10 mm Hg, coronary sinus ( ) diminished from 26±2 to 18±2 mm Hg (–29±2%), coronary sinus O₂ content ( ) increased by 15±3%, myocardial oxygen consumption did not change significantly. The percentage of increase of coronary flow was 23±4%.Analysis of these results with a simple mathematical model of O₂ delivery suggest that increase in affinity is corrected by a simultaneous increase in coronary flow and capillary recruitment.This study was supported by contracts 74-7-0274 from D.G.R.S.T., 76-1-1755 from I.N.S.E.R.M. and a grant from the University of Paris VII     

Expression of calcium channel subunits in the normal and diseased human myocardium

We investigated the expression of ₁ and subunits of the L-type Ca²⁺ channel on the protein level in cardiac preparations from normal human heart ventricles and from the hypertrophied septum of patients with hypertrophic obstructive cardiomyopathy (HOCM). 1,4-Dihydropyridine (DHP) binding and immunorecognition by polyclonal antibodies directed against the C-terminal amino acid sequences of the ₂ and ₃ subunits were used for detection and quantification of ₁, ₂, and ₃ subunits. B_max of high-affinity DHP binding was 35±2 fmol/mg protein in HOCM and 20±2 fmol/mg protein in normal human hearts (P<0.05). In rabbit hearts the anti-₂ subunit antibody immunoprecipitated 80% of the total amount of DHP-labeled Ca²⁺ channels present in the assay. Under identical experimental conditions 25% of labeled Ca²⁺ channels were recovered in the immunoprecipitates of both normal and HOCM ventricles. A similar partial immunoprecipitation was observed in pig hearts. Immunoblot analysis demonstrated that the ₂ subunit was associated with the DHP receptor/Ca²⁺ channel in cardiac muscle of rabbit, pig, and human heart. In neither of these purified cardiac Ca²⁺ channels was the ₃ subunit isoform detected. Our results suggest that both ₁ and ₂ subunit expression is upregulated in HOCM in a coordinate manner.Abbreviations B _max Maximal number of binding sites - DHP 1,4-Dihydropyridine - HOCM Hypertrophic obstructive cardiomyopathy - NH Normal human heart     

Temperature and oxygenation of human blood at constant total CO2 content

The influence of temperature on the oxygeneration of normal and 2,3-diphosphoglycerate-depleted human blood suspensions (final hemoglobin concentration: 0.75%) was studied under closed-system conditions (constant total CO₂ content) beginning with standard values: pH 7.40,P _{CO 2} 40 torr, at 37°C.The present results quantify the temperature-induced changes inP _{O 2} occuring in association with the concomitant acid-base variations prevailing in a closed system. When the temperature was raised from 25 to 42°C,P ₅₀ varied from 13.9±1.1 to 40.7±1.9 torr in the presence of 2,3-DPG and from 7.6±0.4 to 24.8±1.2 torr in the absence of the cofactor.The derived equations correlateP _{O 2} variations with those of temperature (T: 25–42°C) and oxygen saturation (S_{O 2}: 10–90%).The temperature coefficient of oxygenation and the DPG-induced decrease in the heat of hemoglobin oxygenation were shown to be saturation dependent. DPG lowered dlogP _{O 2}/dT from 0.0299 to 0.0275 and H from –12.9 to –11.8 kcal/mole O₂ bound at 50% S_{O 2} but had no significant influence on these parameters for S_{O 2}20%.The results suggest that the release of carbamate at the beginning of oxygenation is virtually unaffected by presence of 2,3-DPG in the 25–42°C temperature range.     

Human corticotropin-releasing factor (hCRF) is a potent respiratory analeptic

Summary During intravenous corticotropin-releasing factor stimulation tests we observed a deepening of the tidal volume in 35 patients. To investigate this presumed respiratory stimulation we measured respiratory parameters in 12 healthy male volunteers in a single-blind placebo-controlled trial. The intravenous 60-s infusion of 100 µg of human corticotropin-releasing factor induced a very potent respiratory stimulation in every subject: respiratory minute volume (mean ± S.D.) increased by 81% from 6.319±0.577 to 11.464±1.264 liters per min (P<0.001), whereas there was only a slight rise in the mean respiratory rate from 12.4±3.0 to 14.7±2.7 breaths per min (P<0.001). Mean tidal volume increased from 531±105 to 809±175 ml (P<0.001). Mean end-tidal partial pressure of carbon dioxide decreased (P<0.001) from 40.3±1.2 to 33.4±1.2 mmHg, whereas mean end-tidal partial pressure of oxygen increased (P<0.001) from 93.2±5.4 to 113.5±5.4 mmHg. After 10 to 20 min both end-tidal carbon dioxide and oxygen partial pressures returned to the baseline values. The placebo had no measurable effects.We conclude that human corticotropin-releasing factor is a potent respiratory stimulant. With 100 µg the resting respiratory minute volume increases by 81%. These data point to the possible importance of the corticotropin-releasing factor as a useful adjunct in the management of patients with alveolar hypoventilation.Abbreviations hCRF human corticotropin-releasing factor - P_ETCO₂ end-tidal partial pressure of carbon dioxide (the last portion of the V_T during expiration, called end-tidal volume, contains CO₂ from the alveolar region) - P_ETO₂ end-tidal partial pressure of oxygen - minute volume - V_T respiratory tidal volume     

Dissociation between antidiuretic response and renal medullary cyclic AMP levels in the rat

Renal tubular bicarbonate reabsorption and acidification were evaluated in phosphate depleted rats (PD) and controls. After 33 days of phosphate depletion, urine pH of PD rats (N=5, 6.36±0.15) was significantly higher than control (N=5, 5.64±0.09,P<0.005) following an NH₄Cl load. Urinary titratable acid of PD rats (9.6±1.8) was significantly reduced compared to control (117.2±19.7 Eq/3 h,P<0.001), whereas NH ₄ ⁺ excretion was not different. The plasma HCO ₃ ^– thresholds at which bicarbonaturia occurred (approximately 25 mEq/l) were identical in controls and phosphate depleted rats during isotonic bicarbonate infusion. The higher urine pH of phosphate depleted rats following NH₄Cl administration was not due to low urinary phosphate as 3-day phosphate depleted rats could normally acidify urine after NH₄Cl (pH=5.86±0.09,N=6 vs. control 5.87±0.08,N=6,P=N.S.) despite urinary phosphate excretion as low as in 33-day PD rats. These data indicate the presence of impaired distal tubular acidification in chronically phosphate depleted rats.Former trainee of the Cardiovascular Research Program and currently a third year medical student at The University of Michigan Medical School.     

Interaction of organic phosphates with bovine hemoglobin

We investigated oxylabile H⁺ binding and pH dependent oxygen binding of adult and newborn bovine hemoglobin as influenced by the organic phosphates 2,3-disphosphoglycerate (DPG), adenosine-5-triphosphate (ATP), and myo-inositol hexaphosphate (IHP).The oxygenaffinity of newborn bovine hemoglobin is higher than that of adult hemoglobin over a pH range of 6.5 to 8. Both DPG and IHP decrease the oxygen affinity of adult bovine hemoglobin. IHP not only decreases the oxygen affinity, but also reduces the apparent cooperativity, whereas DPG does not affect cooperativity. The rise in logP₅₀ upon addition of DPG is about equal for adult and newborn bovine hemoglobin: at pH 7.0 we find logP₅₀ values of 0.14 and 0.13 respectively upon addition of a fivefold excess of organic phosphate. This agrees with the identical nature of the presumed organic phosphate binding site in these two hemoglobins, but contrasts with the situation in man: newborn human hemoglobin is much less influenced by organic phosphates than adult human hemoglobin.Abbreviations Hb (tetrameric) hemoglobin - DPG 2,3-diphosphoglycerate - IHP myo-inositol hexaphosphate - Tris tris(hydroxymethyl)-aminomethane - bis-Tris bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane - Z_H fixed-acid Haldane effect=amount of protons released upon full oxygenation of deoxyhemoglobin (unit: mol·mol^–1) - i _DPG,i _IHP ratio between molar concentrations of DPG and Hb, and IHP and Hb, respectively (unit: mol·mol^–) - P₅₀ oxygen partial pressure at half oxygen saturation of Hb (unit: kPa, mm Hg) - Y percentile oxygen saturation of Hb - T absolute temperature (unit: K)     

Effect of variations in blood hydrogen ion concentration on pulmonary gas exchange of artificially ventilated dogs

The effect of variation of blood hydrogen ion concentration on arterial and mixed venousP _{O 2},ideal alveolar-arterial O₂ pressure difference (P _AiO₂–P _aO₂),venous admixture (Q _s/Q _t), arterio-alveolar CO₂ pressure difference (a–A)D _{CO 2},physiological dead space to tidal volume ratio (V _D/V_T),cardiac output (Q _t) and mean pulmonary arterial pressure ( ) has been studied. Arterial and mixed venousP _{O 2}increased and (P _AiO₂–P _aO₂)decreased with increasing blood hydrogen ion concentration. No change in (Q _s/Q _t), (a–A)-D _{CO 2},V _D/V_T,Q _t and was observed.The effect of hydrogen ion concentration on arterial and mixed venousP _{O 2}and on (P _AiO₂–P _aO₂)is mainly due to a shift of the blood oxyhemoglobin dissociation curve (ODC), i.e. due to the Bohr effect. The upper part of the ODC is more flat in alkalosis (shift to the left) than in acidosis (shift to the right). Therefore the same end-capillary to arterial O₂ content difference results in a greater (P _AiO₂–P _aO₂)in alkalosis than in acidosis. Any factor influencing the slope of the upper part of the ODC is expected to affect the arterialP _{O 2}and the (P _AiO₂–P _aO₂)by this mechanism. Similarly any factor shifting the steep part of the ODC is expected to affect theP _{O 2}of the mixed venous blood.     

Embryonic hemoglobins: dependency of functional characteristics on tetramer composition

1. Nucleated erythroblasts from embryonic rabbits contain two groups of tetrameric hemoglobins (Hbs): Hbs E_I–III consist of embryonic α-type chains (Ξ-chains) and embryonic β-type chains (ε-chains) whilst Hbs L_I–III are composed of adult α-chains and ε-chains. Structural analyses have indicated that the Ξ-chains are evolutionarily older than ε-chains. To obtain informations on possible differences in ligand binding properties associated with these embryonic chains, we have prepared Hbs E_I–III and L_I–III from the erythroblasts of 14-days-old embryonic rabbits and measured their oxygen affinity at various pH values and different concentrations of phosphate compounds. These data were compared with those obtained on the unfractionated embryonic hemolysate and adult rabbit hemoglobin (HbA).
2. We found that Hbs E_I–III have a higher oxygen affinity than Hbs L_I–III at all pH values investigated, the difference becoming larger at more acid pH. As a result, the Bohr effect is smaller in Hbs E_I–III than in Hbs L_I–III, Δ logP ₅₀/Δ pH amounting to ?0.25 and ?0.50, respectively. In the pH range between 6.8 and 7.8 the oxygen affinities of HbA and of Hbs L_I–III are alike but lower in HbA at more acid pH. These results indicate that the presence of embryonic Ξ-chains in hemoglobin tetramers raise the oxygen affinity and lower the Bohr effect of the pigment, whereas the combination of adult α-chains with embryonic ε-chains lead to hemoglobin tetramers with a very similar oxygen affinity to HbA in the physiological pH range. The cooperativity of oxygen binding was smaller both in Hbs E_I–III and L_I–III compared to HbA.
3. The effect of added phosphates notably of 2,3-diphosphoglycerate (2,3-DPG) on the oxygen affinity of Hbs E_I–III and L_I–III was very similar, i.e. the rise inP ₅₀ produced by maximal concentrations of 2,3-DPG was not significantly different in the two types of embryonic hemoglobins. In HbA, the increase ofP ₅₀ produced by comparable concentrations of 2,3-DPG was only slightly higher than in the embryonic hemoglobins. This shows that the embryonic ε-chains are similarly effective in binding phosphate as the adult β-chains.

     

Circannual variation in the expression of β2-adrenoceptors on human peripheral mononuclear leukocytes (MNLs)

Summary Peripheral mononuclear leukocytes (MNLs) are widely used as a tissue model in studies of -adrenoceptor disturbances in hypertension and asthmatic diseases. The ₂-adrenoceptor density (B_max), however, depends not only on the gender of the person under study and on the time of day the blood specimens are obtained. Evidence is now reported for a circannual variation in the expression of ₂-adrenoceptor sites on peripheral MNLs. In male volunteers the 24-h mean was found to be highest in the men studied in April/May (1135±10 sites/cell) and decreased to 891±16 sites/cell in August and to 712±90 sites/cell in December (±SE,P<0.01 April/May compared to December). Concomitantly the circadian amplitude increased from 17.3%±6.4% of 24-h mean in April/May to 28.2%±1.4% of 24-h mean in August and to 34.2%±4.2% of 24-h mean in December (±SE,P<0.05, April/May compared to December). The circadian acrophase remained constant (190°±30° equivalent to 12 h 40 min±2 h 00 min, ±SE).Abbreviations MNLs Peripheral mononuclear leucocytes - B_{max 2}-Adrenoceptor density - ¹²⁵ICYP ¹²⁵Iodo-cyanopindolol - PEF Peak expiratory flow - SE Standard error - ANOVA Analysis of variance - M Circadian mesor - A Circadian amplitude - Circadian acrophase     

Renal intracortical blood flow distribution,function and sodium excretion in response to saline loading of anesthetized and unanesthetized dogs

Summary In order to study the effect of anesthesia on the canine response to saline loading, experiments were performed on 10 dogs, first while awake and then during pentobarbital anesthesia. Individual kidney function and intrarenal blood flow response to saline loading (7.5% body weight) were measured in each condition and all data are reported as the average of a single kidney. C_IN is considerably reduced under anesthesia (24.7±3.2 vs. 43.2±3.9 ml/min,P<0.01). A directionally similar reduction of PAH clearance was noted (89±17 vs. 122±13 ml/min). The natriuretic response to saline loading of the dogs reached 290±61 Eq/min while awake, but only 70±27 Eq/min while anesthetized. No measurable increase of C_IN or C_PAH occurred in response to saline loading either in the anesthetized or unanesthetized state. The natriuresis was entirely due to a rise of C_NA/GFR in both circumstances. The change of C_NA/GFR in response to saline load was also appreciably larger while awake (1.24.7% vs. 0.71.8%). Although the fraction of blood flow to the outermost quarter of the kidney was initially the same (31±3 vs. 29±3%) awake or anesthetized, the changes with saline loading were in the opposite direction and the values reached were significantly different (37±3, awake, vs. 27±3%,P<0.05). We conclude that while increased outer cortical blood flow is not necessary for natriuresis, it may occur during sodium loading and may facilitate sodium excretion.Supported by VA Program 3385-01     

Cellular acidification occurs during anoxia in cultured,but not in freshly isolated,rabbit proximal tubular cells

In a variety of cells it has been shown that acidosis is protective against anoxic injury. We have demonstrated previously that proximal tubule (PT) cells in primary culture were more resistant to anoxiainduced cell injury than were freshly isolated cells. Therefore, we asked the question of whether a difference in cellular acidification during anoxia could explain this difference in susceptibility to anoxia. To answer this question, intracellular pH (pH_i) was measured during anoxic incubation of PT cells in culture and those that were freshly isolated. PT cells were incubated in an anoxic chamber at 37°C after loading with 2,7-bis-(2-carboxyethyl)-5,6-carboxyfluorescein acetoxymethyl ester (BCECF-AM) or fura-2 acetoxymethyl ester (fura-2-AM). pH_i and cytosolic free Ca²⁺([Ca²⁺]_i) were measured by digital imaging fluorescence microscopy. During anoxia, pH_i in cultured PT cells decreased from 7.3±0.1 to 6.8±0.1, whereas pH_i in freshly isolated cells did not decrease significantly. In addition, the intrinsic buffering capacities ( _i) in cultured and freshly isolated PT cells were determined and turned out to be the same at a pH_i greater than or equal to 7.3. Below pH_i 7.3, _i increased several fold in freshly isolated PT cells, and rose to significantly higher levels than in cultured PT cells. During 1 h of anoxia, cell viability of freshly isolated PT cells decreased significantly to 54%±2% (P<0.05), while no loss in viability was observed in cultured PT cells. Clamping the pH_i during anoxia at 6.7 and 6.1 significantly increased cell viability in freshly isolated PT cells to 76%±5% and 72%±4%, respectively (P<0.05). In contrast, prevention of acidification in cultured PT cells during anoxia did not lead to increased cell death. Therefore, the differences in susceptibility to anoxic injury between cultured and freshly isolated PT cells cannot be explained by cellular acidification in cultured cells, but must be sought elsewhere.     

The numerical study on the effects of cardiac function on the aortic oxygen distribution

Although venoarterial extracorporeal membrane oxygenation (VA-ECMO) was widely used in clinical practice, the effects of cardiac output on the aortic oxygen distribution were still unclear. Hence, the present study aims to evaluate the effect of cardiac function on the aortic oxygen distribution under VA-ECMO support. A novel model, combining computational fluid dynamics, multiphase fluid approach, and oxygen transport theory together, was established. According to the clinical practice, four cardiac output conditions, including 0, 1, 2, and 2.5 L/min, were designed. The results demonstrated that the proposed method could accurately calculate the distribution of oxygen in the aorta. Moreover, the aortic oxygen distribution was significantly regulated by the local blood flow pattern. The deoxygenated blood flow and oxygenated blood flow met at the aortic arch and formed the so-called oxygenshed phenomenon. Along with the cardiac output increase, the oxygenshed was moved from the proximal of the aortic arch to the descending aorta. Meanwhile, the oxygen contents in the brachiocephalic artery and left common carotid artery were reduced along with the increase of cardiac output. The study could provide much useful information on the oxygen distribution in the aorta to surgeons and operators of VA-ECMO.

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Graphical abstract The results showed the deoxygenated blood and oxygenated blood met at the aortic arch and formed the so-called “oxygenshed” phenomenon. This phenomenon is consistent with the phenomenon called “watershed”

     

Maximal accumulated oxygen deficit expressed relative to the active muscle mass for cycling in untrained male and female subjects

The purpose of the present study was to determine if gender differences exist in the maximal accumulated oxygen deficit (MAOD) or in the blood lactate (Lac^?) and catecholamine responses to the MAOD test (120% peak oxygen uptake to exhaustion). The MAOD for cycling was measured in ten untrained male and ten untrained female subjects using the method described by Medbø et?al. (Anaerobic capacity determined by maximal accumulated oxygen deficit. J Appl Physiol 64: 50–60, 1988). Blood Lac^? and catecholamine concentrations were measured at rest, exhaustion and for 30?min following the MAOD test. Dual-energy X-ray absorptiometry was used to measure lean body mass (LBM) and to estimate the active muscle mass (AMM) for cycling. Males achieved a significantly higher MAOD than females following correction for AMM [126.3 (5.6) versus 108.3 (6.1)?ml?·?kg AMM^?1, P=0.04]. The peak blood lactate concentration ([Lac^?]) in males [13.6 (0.9)?mmol?·?l^?1] was significantly higher than in females [10.0 (1.0)?mmol?·?l^?1]. Males obtained a 68% higher peak epinephrine concentration ([Epi]) than females, but the difference was not significant [1268 (188)?pg?·?ml^?1 versus 755 (179)?pg?·?ml^?1, P=0.066]. However, plasma [Epi] was significantly higher for males than females at 1?min [824 (116) versus 489 (116)?pg?·?ml^?1, P=0.036] and 3?min [330 (52) versus 179 (42)?pg?·?ml^?1, P=0.039] into the recovery period. No gender-dependent differences in the norepinephrine concentration were observed at any time. Peak [Lac^?] was significantly correlated with MAOD (ml?·?kg AMM^?1) in females (r=0.75), but not in males (r=0.09). The peak plasma [Epi] was not significantly correlated with MAOD (ml?·?kg AMM^?1) or peak [Lac^?] in either group. These findings suggest that there are gender-dependent differences in MAOD even when expressed relative to the AMM for cycling. The higher blood [Lac^?] in males compared to females obtained after supramaximal exercise was not caused by enhanced secretion of Epi. The greater MAOD in untrained males was not caused by a greater ability to produce Lac^? or by enhanced secretion of Epi.     

Relationship between muscle fatigue and oxygen uptake during cycle ergometer exercise with different ramp slope increments

Summary The surface electromyogram (EMG) from active muscle and oxygen uptake ( ) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W · min^–1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMG_bp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake ( ) and the iEMG_bp between 10 and 30, and 10 and 40 W · min –1 ramp exercises (P < 0.05). However, no significant differences were obtained in and corresponding to the iEMG_bp during the four ramp exercises. With respect to the relationship between and exercise intensity during the ramp increments, the -exercise intensity slope showed significant differences only for the upper half (i.e. above iEMG_bp). These results demonstrated that the and at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to and the iEMG_bp was varied by the change of ramp slopes. In addition, the significant differences in the exercise intensity slopes for the upper half of the tests would suggest that the recruitment patterns of MU and/or muscle metabolic state might be considerably altered depending upon the ramp slope increments.     

Increased serum urate in galactosemia patients after a galactose load: A possible role of nucleotide deficiency in galactosemic liver injury

Summary Five galactosemic and 5 normal children received an oral load of galactose under standardized conditions. The maximal blood galactose level after 1.5 hours was 12.6±2.0 (S.D.) mmol/l in individuals with a deficiency of uridylyl transferase (EC2.7.7.12) as compared to 5.8±1.2 (S.D.) mmol/l in the controls. The concentration of serum urate in galactosemics increased to 155% of the fasting level (P<0.005); no rise was detectable in the controls. The elimination of urate with the urine was augmented by the same amount in both groups. Our studies provide evidence for an increased catabolism of hepatic nucleotides. This may lead to a deficiency of nucleotides which is proposed as a cause of galactosemic liver injury.This work was supported by grants from the Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg, Ke 200/3, and Forschergruppe Leberkrankheiten, Freiburg.     

Sex differences in the oxygen affinity of hemoglobin

Summary The oxygen dissociation curves of 50 healthy young nonsmokers 25 women and 25 men, were investigated. The following parameters were deter-mined: hemoglobin concentration, microhematocrit, red cell count, mean corpuscular hemoglobin concentration, capillary blood pH,P ₅₀ value, and the concentration of red cell 2,3-diphosphoglycerate. P ₅₀ values are significantly higher in the female group (28.3 mm Hg±0.4 S.E.M.) than in the male group (26.3 mm Hg±0.4 S.E.M.), indicating a lower oxygen affinity of hemoglobin in females.There is no significant difference between the DPG values. No significant negative correlation exists between the Hb concentration and theP ₅₀ values.with the technical assistance of Monika Humpeler and Edith Gasser