Kinetics of 13CO2 elimination after ingestion of 13C bicarbonate: the effects of exercise and acid base balance

Abstract. In order to investigate the effects of muscular work and preceding exercise on the retention of exogenous labelled bicarbonate, we studied the effects of oral administration of [¹³C]bicarbonate (0·1 mg kg^-1) in five subjects at rest before exercise and during and after 1 h of treadmill walking at 73% VO_2max on three separate occasions. Elimination of CO₂ from labelled bicarbonate was 62·6±8·1% at rest, 103·6±11·3% during exercise (P<0·01) and 43·0±4·7% during recovery from exercise (P= 0·01). During exercise mean residence time (MRT) was shorter than at rest (35±7 min vs. 54±9min, P < 0·02) and CO₂ pool size was larger (998±160 ml CO₂kg^-1, vs. 194±28ml CO₂kg^-1, P < 0·001). Compared to values obtained at rest, during recovery from exercise, MRT and CO₂ pool size were reduced (34±5min, P < 0·05; 116±19 ml CO₂kg^-1, P < 0·02, respectively). In an additional five subjects acidosis and alkalosis were induced prior to administration of oral [¹³C]bicarbonate at rest. Elimination of bicarbonate was lower during acidosis (46·1±5·6%, P < 0·01) but was unaltered (50·9±5·6%, NS) during alkalosis, compared to the values obtained at resting pH. During acidosis MRT and CO₂ pool size decreased (37±3min, P<0·01 and 123±10ml CO₂kg^-1, P < 0·01, respectively) whereas in alkalosis MRT was unchanged (65±8 min NS) but CO₂ pool size was increased (230±23ml CO₂kg^-1, P < 0·05). The kinetics of elimination of ¹³CO₂ from administered bicarbonate after exercise are different to those at rest and resemble acidosis. The appropriate correction factor for sequestered ¹³C should be used in metabolic studies of the post-exercise state when using ¹³C tracers.     

The interplay between metabolic alterations,diastolic strain rate and exercise capacity in mild heart failure with preserved ejection fraction: a cardiovascular magnetic resonance study

Background

Heart failure (HF) is characterized by altered myocardial substrate metabolism which can lead to myocardial triglyceride accumulation (steatosis) and lipotoxicity. However its role in mild HF with preserved ejection fraction (HFpEF) is uncertain. We measured myocardial triglyceride content (MTG) in HFpEF and assessed its relationships with diastolic function and exercise capacity.

Methods

Twenty seven HFpEF (clinical features of HF, left ventricular EF >50%, evidence of mild diastolic dysfunction and evidence of exercise limitation as assessed by cardiopulmonary exercise test) and 14 controls underwent ¹H-cardiovascular magnetic resonance spectroscopy (¹H-CMRS) to measure MTG (lipid/water, %), ³¹P-CMRS to measure myocardial energetics (phosphocreatine-to-adenosine triphosphate - PCr/ATP) and feature-tracking cardiovascular magnetic resonance (CMR) imaging for diastolic strain rate.

Results

When compared to controls, HFpEF had 2.3 fold higher in MTG (1.45?±?0.25% vs. 0.64?±?0.16%, p?=?0.009) and reduced PCr/ATP (1.60?±?0.09 vs. 2.00?±?0.10, p?=?0.005). HFpEF had significantly reduced diastolic strain rate and maximal oxygen consumption (VO₂ max), which both correlated significantly with elevated MTG and reduced PCr/ATP. On multivariate analyses, MTG was independently associated with diastolic strain rate while diastolic strain rate was independently associated with VO₂ max.

Conclusions

Myocardial steatosis is pronounced in mild HFpEF, and is independently associated with impaired diastolic strain rate which is itself related to exercise capacity. Steatosis may adversely affect exercise capacity by indirect effect occurring via impairment in diastolic function. As such, myocardial triglyceride may become a potential therapeutic target to treat the increasing number of patients with HFpEF.

     

Muscle glycogen does not interfere with a 13CO2 breath test to monitor liver glycogen oxidation

Naturally ¹³C‐enriched carbohydrate has been used to label the liver glycogen pool for metabolic studies. The utilization of this glycogen was then monitored by the appearance of ¹³CO₂ in breath. Using this method, it is assumed that during sedentary fasting the contribution of muscle glycogen towards oxidation is negligible. We investigated the influence of a different level of ¹³C enrichment of muscle glycogen on the ¹³C enrichment of breath CO₂ while the breath test was carried out. In six healthy volunteers, the muscle glycogen stores were grossly depleted by a cycling exercise prior to consumption of the ¹³C‐enriched diet which was given over a 10 h period. The oxidation of liver glycogen was measured during an 18 h sedentary fast. The results were compared with a control group who had not depleted their muscle glycogen before labelling. A higher ¹³C enrichment of muscle glycogen did not interfere with two parameters of liver glycogen oxidation, i.e. the duration of the plateau phase of ¹³CO₂ and the return to baseline time. It was also shown that the ¹³C‐labelled muscle glycogen was still available after the 18 h fast because a strenuous exercise led to a rapid ¹³CO₂ enrichment. It is concluded that muscle glycogen ¹³C enrichment does not invalidate a ¹³CO₂ breath test to measure liver glycogen oxidation during a sedentary fast.     

Met5-enkephalin-Arg6-Phe7 (MEAP): A Cardioprotective Hormonal Opioid

Background: Acute myocardial ischemia is an important cause of morbidity and mortality worldwide. The heart and other organs can be rendered more resistant to the deleterious effects of ischemia through a variety of preconditioning strategies, including treadmill exercise and brief ischemia of skeletal muscle. Some of the beneficial effects of these preconditioning strategies appear to be mediated by as‐of‐yet unidentified hormonal opioids. Objectives: To test the hypothesis that endogenous opioids of the enkephalin class are capable of improving ischemic tolerance and acting in a hormonal manner. Methods: In phase one of the investigation, the authors assessed the cardioprotective potential of all four known enkephalins. This was achieved by subjecting isolated buffer‐perfused rabbit hearts to a 25‐minute period of test ischemia and two hours of reperfusion (protocol 1) after receiving treatment with either saline vehicle (controls) or increasing concentrations of purified enkephalins. On the basis of results from these initial studies, the authors performed additional experiments (protocol 2) to determine whether Met⁵‐enkephalin‐Arg⁶‐Phe⁷ (MEAP) could be absorbed from skeletal muscle and exert a cardioprotective effect. Specifically, MEAP or vehicle (controls) was given intramuscularly 24 hours before the hearts were harvested. A similar assessment of ischemic tolerance as described in protocol 1 was then performed. Postischemic myocardial viability (infarct size) was assessed in all cases by triphenyltetrazolium chloride (TTC) staining. Hemodynamic parameters and infarct sizes for concentration‐dependence studies were compared by two‐way analysis of variance, and infarct sizes from protocol 2 studies were compared by using Student's t‐test (significance set at p ≤ 0.05). Results: Mean infarct size in control hearts (± SEM) was 33% (± 4%) and 36% (± 6%) for protocol 1 and 2, respectively. Of the four enkephalins tested in protocol 1, only MEAP treatment showed a tendency toward cardioprotection. Interestingly, an alternative enkephalin, methionine⁵‐enkephalin‐Arg⁶‐Gly⁷‐Leu⁸, tended to exert an injurious effect. In protocol 2, MEAP treatment 24 hours before ischemia significantly reduced infarct size (14%± 4%) compared with controls, suggesting that it can be released from muscle and exert a distant cardioprotective effect. Conclusions: When given either directly to the heart or absorbed from a distant tissue, MEAP induces cardioprotection, supporting the hypothesis that it can act as a hormonal modulator of ischemic tolerance.     

Defects of β2-adrenergic signal transduction in chronic lymphocytic leukaemia: relationship to disease progression

The second messenger 3′:5′-cyclic adenosine monophosphate (cAMP) inhibits the proliferation of human B lymphocytes. In lymphoid malignancies, cAMP levels or the number of β₂-adrenergic receptors seem to be decreased. In order to explore this phenomenon further, the function of the β₂-adrenergic receptor complex was examined in mononuclear leucocytes (MNLs) from patients with B-cell chronic lymphocytic leukaemia (CLL). Peripheral blood MNLs from 25 CLL patients (16 male, nine female; aged 62 ± 9 years) and 10 healthy volunteers (seven male, three female; aged 47 ± 19 years) were used. The binding characteristics of β₂-adrenergic receptors (β₂-AR) on MNLs were determined by radioligand binding assays with [¹²⁵I]-cyanopindolol ([¹²⁵I]-CYP). The number of high-affinity binding sites for [¹²⁵I]-CYP was significantly lower in CLL patients (313 ± 300 sites per cell; mean ± SD) than in control subjects (1479 ± 1268 sites per cell). Moreover, the density of β₂-AR decreased with disease progression, from Binet stage A (371 ± 236, n = 13) to B (236 ± 136, n = 7) and C (141 ± 59, n = 5) (P < 0.05; Kruskal–Wallis analysis). Functional analyses of the β₂-AR complex were performed by measuring the cellular cAMP content of MNLs in response to different stimulators. The cAMP production of MNLs upon isoprenaline stimulation (ISO; 10 min, 10^?4 mol L^?1) was slightly lower in CLL patients (12.5 ± 7.04 pmol 10^?6 cells) than in control subjects (15.91 ± 10.08 pmol 10^?6 cells), and decreased with CLL progression (stage A 14 ± 7; stage B 13.66 ± 3.91; stage C 3.07 ± 0.79 pmol 10^?6 cells). In contrast, cAMP accumulation in response to cholera toxin (CHO; 10^?4 g ml^?1, 120 min) was not different in control subjects (70.07 ± 31.30 pmol 10^?6 cells) and CLL patients (stage A 95.24 ± 123.07 , stage B 70.76 ± 57.37, stage C 33.21 ± 33.73 pmol 10^?6 cells). When stimulated with forskolin (100 μmol L^?1, 15 min), control MNLs produced about ten-fold more cAMP than CLL MNLs (188.56 ± 92.53 vs. 17.88 ± 10.32 pmol 10^?6 cells); this response was not stage dependent. Taken together, the results show that the β₂-AR transmembrane signalling is impaired in CLL patients. The correlation of some β₂-AR signalling defects with disease progression suggests that they may contribute to the disease progression of CLL patients.     

Acute saline infusion induces extracellular acidification and activation of the Na+/H+ exchanger in man

The effect of acute expansion of the extracellular fluid volume (ECV) with isotonic (0.9%) saline on the activity of the lymphocyte Na⁺/H⁺ antiport (NHE) was studied in a total of 18 healthy volunteers. Saline was infused at a constant rate so that 4 mmol kg^?1 b.w. was administered over 2 h. NHE activity was measured by quantifying cytosolic pH (pH_i) recovery following acidification of the cells with propionic acid and by pH clamping at various pH_i values between 7.2 and 5.8 using nigericin. Both methods demonstrate NHE activation associated with intravenous saline infusion, the kinetic difference being a marked decrease in the Hill coefficient n from 3.28 ± 0.21 (SEM) to 2.22 ± 0.11 in the absence of changes in baseline pH_i (7.14 ± 0.02 vs. 7.08 ± 0.02; P = 0.15), V_max (42.8 ± 2.7 vs. 48.1 ± 2.8 mmol L^?1 min^?1; P = 0.08) and pK (6.32 ± 0.04 vs. 6.35 ± 0.02). NHE activation was associated with significant decreases in serum chloride (P = 0.016), calcium (P = 0.008), total cholesterol (P = 0.008), low-density lipoproteins (P = 0.016) and high-density lipoproteins (P = 0.008). Moreover, saline infusion induced extracellular acidification with a decrease in pH from 7.39 ± 0.01 to 7.37 ± 0.01 (P = 0.016), HCO₃^? from 23.3 ± 0.43 mmol L^?1 to 21.3 ± 0.25 mmol L^?1 (P = 0.008) and base excess from ?1.03 ± 0.38 mmol L^?1 to ?3.00 ± 0.31 mmol L^?1 (P = 0.008). Our results show for the first time that acute ECV expansion with isotonic saline is followed by an activation of the lymphocyte NHE. The underlying mechanism(s) remain to be investigated. However, the demonstration in our study of marked changes in acid–base balance induced by acute saline points to a possible inter-relationship of antiporter activation and extracellular acidification.     

Non-invasive cardiac output assessment during moderate exercise: pulse contour compared with CO2 rebreathing

The arterial pulse contour method called Modelflow 2·1 calculates stroke volume continuously, beat to beat, from the non-invasive blood pressure signal measured by Finapres or Portapres. Portapres is the portable version of Finapres. The purpose of this study was to compare cardiac output (CO) calculated using Modelflow 2·1 (CO_mf) with CO obtained by the CO₂ rebreathing method (CO_re) during steady state at moderate exercise levels. Twelve subjects visited the laboratory twice and performed submaximal exercise on a bicycle ergometer at 20%, 40% and 60% of their individual peak power output (PO_peak). The averaged correlation between CO_mf and CO_re gives an r-value of 0·69, whereas the slope and intercept of the regression line were 1·06 and 1·65 respectively. The averaged difference between CO_mf and CO_re was 2·27 ± 3·9 l min^–1 (mean ± standard deviation). However, the test–retest difference between CO_mf and CO_re was 2·5 ± 3·1 and 0·5 ± 1·3 l min^–1 respectively. These results suggest that Modelflow 2·1 is not an accurate method for estimating CO from non-invasive blood pressure data collected by Portapres during exercise at up to 60% of the individual PO_peak corresponding with daily life activity.     

Assessment of a new prototype hydrogel CO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript> sensor; comparison with air tonometry

Objective

Gastrointestinal ischemia is always accompanied by an increased luminal CO₂. Currently, air tonometry is used to measure luminal CO₂. To improve the response time a new sensor was developed, enabling continuous CO₂ measurement. It consists of a pH-sensitive hydrogel which swells and shrinks in response to luminal CO₂, which is measured by the pressure sensor. We evaluated the potential clinical value of the sensor during an in vitro and in vivo study.

Methods

The response time to immediate, and stepwise change in pCO₂ was determined between 5 and 15 kPa, as well as temperature sensitivity between 25 and 40 °C at two pCO₂ levels. Three sensors were compared to air tonometry (Tonocap^®) in healthy volunteers using a stepwise incremental exercise test, followed by a period of hyperventilation and an artificial CO₂-peak.

Results

The in vitro response time to CO₂ increase and decrease was mean 5.9 and 6.6 min. The bias, precision and reproducibility were +5%, 3% and 2%, resp. Increase of 1 °C at constant pCO₂ decreased sensor signal by 8%. In vivo tests: The relation with the Tonocap was poor during the exercise test. The response time of the sensor was 3 min during hyperventilation and the CO₂ peak.

Conclusion

The hydrogel carbon dioxide sensor enabled fast and accurate pCO₂ measurement in a controlled environment but is very temperature dependent. The current prototype hydrogel sensor is still too unstable for clinical use, and should therefore be improved.

     

Gastric emptying measurement of liquid nutrients using the 13C-octanoate breath test in critically ill patients: a comparison with scintigraphy

Purpose

Scintigraphy is considered the most accurate technique for the measurement of gastric emptying (GE) but, for patients in the intensive care unit, it is technically demanding, involves radiation and can interfere with care. The ¹³C-octanoate breath test (¹³C-OBT) is a simple, non-invasive technique that does not involve radiation exposure.

Aim

To evaluate the performance of the ¹³C-OBT in the assessment of GE in critically ill patients.

Methods

The GE was assessed in 33 mechanically ventilated patients (23 M; 54.3 ± 3.0 yrs; APACHE II: 22.0 ± 1.1). Following test meal administration (100 ml Ensure^®), concurrent scintigraphic measurement and breath samples (¹³C-OBT) were collected over 4 h. Scintigraphic meal retention was determined and the gastric emptying coefficient (GEC) and half emptying time [t50_(BT)] were calculated for the ¹³C-OBT. Delayed GE was defined as meal retention >13 % at 180 min.

Results

Delayed GE was identified in 27/33 patients. Meal retention correlated modestly with t50_(BT) (r = 0.55–0.66; P < 0.001) and well with GEC (r = ?0.63 to ?0.74; P < 0.0001). The strength of agreement between the two techniques was highest between GEC and retention at 120 min. The best cut-off GEC for defining delayed GE was 3.25 (AUC = 0.75; 95 % CI = 0.52–0.99; P = 0.05), with 89 % sensitivity and 67 % specificity to detect delayed GE. The GE was delayed in all (23/23) patients with feed intolerance (GRV > 250 ml) on scintigraphy and 91 % (21/23) patients on ¹³C-OBT.

Conclusion

In critical illness, there was a correlation between ¹³C-OBT and gastric scintigraphy, with GEC performing as a better and more sensitive marker of detecting delayed GE than t50. However the relatively wide 95 % confidence intervals suggest that ¹³C-OBT is more suitable as a technique to assess GE in a group setting for research studies rather than for individual patients in clinical practice.     

Influence of the endothelium on Ca2+ dependency of angiotensin II-induced contractions of rat aortic rings

Summary— Endothelium-dependent relaxation has been demonstrated to be involved in the regulation of vascular tone and extracellular Ca²⁺ was found to play a prominent role in this process. Since the dependency on extracellular Ca²⁺ appeared to differ considerably within the arterial tree, possibly as a consequence of vessel-related endothelium-dependent mechanisms, we investigated the effects of different compounds affecting Ca²⁺ entry (nifedipine, CoCl₂) on angiotensin II-induced contractions of rat aortic rings with and without endothelium as well as the responses in a Ca²⁺–“free” solution. For this purpose, rat aortic rings were either undone from their endothelial layer by gentle mechanical rubbing or care was taken to keep the intima intact in case rings where endothelium were required. The presence of an intact endothelium was confirmed by acetylcholine-induced relaxation. A stronger responsiveness towards angiotensin I, both after a complete concentration-response curve and after a single maximal concentration of angiotensin II was observed in arterial segments without endothelium. The maximal contraction to a single concentration of angiotensin II (0.1 μM) in the rings without endothelium amounted to 75.8 ± 3.8% of the preceding response to a supramaximal concentration of noradrenaline (= E_max). In rings without the endothelial layer, the contraction was 34.8 ± 3.7% of E_max. This indicates an endothelium-induced relaxation in aortic rings with endothelium. After incubation with the Ca²⁺ entry blocker nifedipine (1 μM) both rings with and without endothelium were inhibited to the same extent, contractions amounted to 30.7 ± 1.8% and 19.6 ± 1.3% of E_max, respectively. However, incubation in a Ca²⁺-“free” medium for 5 min resulted in similar contractions for rings without endothelium (16.4 ± 1.4% of E_max) as for rings with endothelium (15.0 ± 1.6% of E_max). Moreover, CoCl₂ in a concentration of 300 μM hardly inhibited the contraction of rings with an intact endothelium, a contractile response of 30.5 ± 2.8% of E_max was observed. The results of the study suggest that the influx of Ca²⁺ions is indeed responsible for the endothelium-mediated relaxation. However, this influx, which cannot be antagonized by nifedipine, but has shown to be affected by CoCl₂, suggests that channels intensitive to organic Ca²⁺ entry blockers may be involved.     

Diet-induced thermogenesis in well-trained subjects

Summary. The purpose of this study was to examine the possible relationship between the thermogenic response to a mixed meal and the aerobic capacity in healthy subjects. Fourteen male subjects participated, and their maximal oxygen uptake was determined on a bicycle exercise ergometer. Two groups, each comprising seven individuals, were compared: a well-trained group, with an oxygen uptake of 58·2 ml min ^-1 kg^-1 and a sedentary group, with an oxygen uptake of 39·2 ml min^-1 kg^-1. Respiratory gas exchange was measured continuously for 1 h in the basal state and then for 3 h postprandially. The subjects ingested a test meal in liquid form, consisting of 17% kJ protein, 28% kJ lipids and 55% kJ carbohydrates, and corresponding to 60% of the individually computed 24-h basal energy expenditure. Basal oxygen uptake and energy expenditure were similar in the two groups. After the meal, pulmonary oxygen uptake and energy expenditure rose rapidly and reached a plateau after 1 h. The responses were no different in the two groups: the average rise in pulmonary oxygen uptake above basal during the whole study period was 24.0±2.1% in well-trained and 26.7±1.5% in sedentary subjects (NS); the corresponding values for energy expenditure were 25.0±2.1% and 29.0±1.6% (NS). Also, when expressed in absolute terms the increments above basal were not significantly different. There was no discernible relationship between the individual thermogenic response and maximal oxygen uptake. In conclusion, the present findings do not indicate that diet-induced thermogenesis is proportional to aerobic capacity in healthy young men.     

Use of prostaglandin E1 during preparation of platelet concentrates

Summary. A paired study in 10 autologous volunteer donors was undertaken to investigate the efficacy of adding prostaglandin E₁ (PGE₁) in vitro during routine platelet concentrate (PC) production. After 5 days storage, PCs prepared with PGE₁ were compared with control PCs. In vivo platelet recovery, survival and biodistribution were determined following autologous infusion of indium-111 labelled platelets into volunteers, together with the in vitro evaluation of platelet function and biochemistry. PGE₁ facilitated easier and faster platelet resuspension following centrifugation. After storage there were few significant in vitro differences between PCs prepared with PGE₁ and control PCs. The artifactual leucocyte concentration was significantly lower in the presence of PGE₁, suggesting less platelet aggregates had been formed during storage and β-thromboglobulin release was significantly reduced by PGE₁, 14.0±6.0 μg per 10⁹platelets compared with 22.3±9.8μg per 10⁹platelets in control PCs, (P < 0.01), indicating PGE₁ reduced both platelet aggregation and activation probably at the initial preparation stage, known to produce the greatest trauma. Initial in vivo platelet recovery for PCs prepared with PGE₁ was similar to that of control PCs, 41.1 ± 12.5% vs. 44.4±80%, respectively, and there were no differences in organ distribution at 24h. However, in vivo multiple hit survival was reduced in the presence of PGE₁, 5.8 ± 1.6 days compared with 6.9 ± 1.4 days in control PCs (P < 0.05). Despite the ability of PGE₁ to facilitate platelet resuspension and inhibit platelet aggregation and activation during preparation of the PCs, the reduced in vivo survival time may preclude the use of PGE₁ during routine PC preparation.     

Triiodothyronine and amiodarone effects on β3-adrenoceptor density and lipolytic response to the β3-adrenergic agonist BRL 37344 in rat white adipocytes

Summary— The β-adrenergic effects of catecholamines are potentiated by thyroid hormones in adipose tissue. Amiodarone (AM) is structurally similar to thyroid hormones and was used to explore the mechanism of the triiodothyronine (T₃) effect on β-adrenergic receptors (β-ARs) in adipose tissue. AM decreases the expression of some T₃ sensitive genes in various tissues and antagonizes the effect of T₃ on its nuclear receptors. In this study, the T₃, AM and AM + T₃ effects on the β1- and β₃-AR density were assessed on rat white adipocytes by radioligand binding using [³H]CGP 12177 after characterization of these subtypes by displacement of [³H]CGP 12177 binding by isoproterenol, BRL 37344 and noradrenaline. BRL 37344 was used to study β₃-AR lipolysis. White adipocytes from hyperthyroid rats had increased responsiveness (E_max × 2) and sensitivity (+ 38%) to BRL 37344, while those given AM alone had decreased values. Moreover, AM antagonized the T₃ effect on lipolysis. The β₁-binding characteristics (receptor density [B_max]: 45 ± 4 fmol/mg of proteins; dissociation factor [K_d]: 0.96 ± 0.10 nM) were not modified by either compound. Finally, T₃ significantly increased β₃-AR density (587 ± 69 versus 363 ± 25 fmol/mg of proteins) and K_d (38 ± 2 versus 23 ± 3 nM), while AM alone had no effect and did not antagonize the T₃ effect on β₃-AR number. In conclusion, the hyperthyroid state in the rat potentiated the lipolytic response of white adipocytes to a specific β₃-agonist and increased the β₃-AR density without changing in β₁-AR number and affinity. Furthermore, the lack of antagonism between AM and T₃ on β₃-AR expression suggests that T₃ does not work directly on the β₃-AR gene. Moreover, AM induced a functional tissular hypothyroid-like effect and its antilipolytic effect probably occurred at a postreceptor level.     

Effects of infused glucose on glycogen metabolism in healthy humans

SUMMARY. In order to determine whether or not hepatic glycogen breakdown contributes to systemic glucose flux during glucose infusion, net carbohydrate oxidation (indirect calorimetry) and the total rate of glucose appearance (6,6^-2H-glucose) were measured in six healthy women during infusion of U^-13C labelled glucose (22 μmol/kg/min). Glucose infusion completely suppressed endogenous glucose production and increased net carbohydrate oxidation from 10.9±l.6 to 18.9±l.0 μmol/kg/min. To differentiate between the oxidation of endogenous (i.e. glycogen) and of exogenous carbohydrates, the ¹³CO₂ production was measured and the oxidation of exogenous ¹³C labelled carbohydrate was calculated. For this purpose, the specific recovery factor in breath of ¹³CO₂ issued from oxidation of uniformly labelled glucose was determined during infusions of equimolar amounts of ¹³C bicarbonate, 1-¹³C acetate and 2-¹³C acetate. The average recovery was 53.9±l.5%. The oxidation of exogenous carbohydrate was 20.9±0.74μmol/kg/min. This value was slightly higher than net carbohydrate oxidation, indicating that no oxidation of endogenous, unlabelled carbohydrate, and, hence, no utilization of hepatic glycogen took place. These results indicate that (i) estimation of glucose oxidation from indirect calorimetry and tracer technology give concordant results when an appropriate factor of ¹³CO₂ recovery in breath is used, and (ii) utilization of previously formed glycogen is inhibited during hyperglycaemia and hyperinsulinaemia.     

Metabolic adaptations in post-exercise recovery

Summary. To investigate further the hormonal and metabolic adaptations occurring when carbohydrates are ingested after prolonged exercise, we have compared the fate of a 100-g oral glucose load (using ‘naturally labelled’¹³C-glucose) in healthy volunteers after an overnight fast at rest either without previous exercise or after a 3-h exercise performed on a treadmill at about 50% of the individual V?o₂ max. In comparison to the control conditions, the oral glucose tolerance test (OGTT) performed in the post-exercise recovery period was characterized by a greater rise in peripheral blood glucose levels and delayed insulin response. Plasma glucagon values were significantly elevated at the time glucose was given (+48 ±13 pg ml^-1) and at the end of the OGTT. Plasma-free fatty acid (FFA) levels were 1675 ± 103 μEq 1^-1 when glucose was given, and subsequently reduced to values similar to those observed in the control conditions. Indirect calorimetry indicated that OGTT in post-exercise recovery was associated with decreased carbohydrate and increased lipid oxidation when compared to control conditions. Exogenous glucose oxidation was also significantly reduced: 25·1 ± 2·6 vs. 35·9 ± 1·9 g per 7 h. We suggest that the higher plasma glucagon levels and the delayed insulin response played a role in the decreased hepatic glucose retention previously described by others in post-exercise recovery. Our data also suggest that the higher lipid oxidation rate observed at the time glucose was given in the post-exercise period could explain, according to the Randle ‘glucose-fatty acid cycle’, the decreased carbohydrate oxidation and the preferential muscle glycogen repletion already well documented. The reason why the lipid oxidation rate remains increased 3–7 h after glucose ingestion in spite of the fact that FFA levels at that time are similar to those observed in control conditions is still unknown; further kinetic studies are needed to clarify this point.     

The lymphocyte Na+/H+ antiport: activation in primary hypertension and during chronic NaCl-loading

Abstract. Increased activity of the Na⁺/H⁺ antiport may be a major abnormality in essential hypertension. The activity of this transport system was investigated in lymphocytes from 13 patients with untreated essential hypertension (Ht) and 13 normotensive control subjects (Nt) on an ad libitum (130–170 mmol d^-1) NaCl intake. Furthermore, the effects of different states of NaCl balance on lymphocyte Na⁺/H⁺ antiport were evaluated in two groups of Nt volunteers receiving 20 vs. 300 mmol d^-1 (n= 8) and 85 vs. 200 mmol d^-1 (n= 14) of NaCl for 1 week each and in seven Ht patients (20 vs. 300 mmol NaCl d^-1 for 1 week each). Additionally, during the 20 and 300 mmol/d NaCl intake red blood cell membrane transport was studied in eight subjects. For the determination of lymphocyte antiport activity, cells were loaded with the cytosolic pH (pH_i) indicator bis-carboxyethyl carboxyfluorescein (BCECF-AM) and acidified by addition of different amounts of Na⁺-propionate (5–40 mM). Initial pH_i-recovery was taken as the activity of the antiport system and plotted against pH_i-values after acidification. Non-linear regression analysis yielded higher ’apparent’ maximal transport rates in Ht than Nt (Nt: 2·00 pL 0·22; Ht: (3·81 pL 0·59)·10^-3 s^-1; P < 0·025). In contrast, baseline pH_i-values and pH_i-values at half-maximal activity (pK) were identical in Nt and Ht. In normotensive control subjects on an NaCl intake of 20, 85, 200 and 300 mmol d^-1 for 7 d, ’apparent’ maximal transport rates averaged 2.75 0·20, 2·89 0·17, 2·81 ± 0·18 and (3·62 ± 0·25) · 10^-3 s^-1, respectively. Thus, antiport activity was significantly (P < 0·05) stimulated on the 300 mmol d^-1 intake as compared to the three other NaCl intakes. The extreme intakes of NaCl (20 vs. 300 mmol d^-1) in normotensive volunteers did not affect the erythrocyte Na⁺/K⁺ pump, Na⁺/K⁺ cotransport and Na⁺/Li⁺ countertransport. Our study supports the concept that a group of patients with primary hypertension exhibit an activated Na⁺/H⁺ antiport. Furthermore, our data demonstrate that a chronic high intake of NaCl is associated with an increase in lymphocyte antiport activity towards the high values observed in primary hypertension.     

Endogenous α2-antiplasmin does not enhance glomerular fibrin deposition or injury in glomerulonephritis

Summary. Background: Fibrin deposition is an important mechanism of glomerular injury in crescentic glomerulonephritis (GN), a severe form of immune renal injury. Both coagulation and fibrinolysis (via the plasminogen–plasmin system) are important in net glomerular fibrin accumulation in GN. α₂‐Antiplasmin (α₂‐AP) is the major circulating inhibitor of plasmin and is expressed in the renal tubulointerstitium. Objective: To determine whether endogenous α₂‐AP contributes to glomerular fibrin accumulation in GN. Methods: Crescentic autologous phase antiglomerular basement membrane GN was induced in mice with intact and deficient endogenous α₂‐AP (α₂‐AP^+/+ and α₂‐AP^?/? mice). Results: In mice with crescentic GN, α₂‐AP was detected in the tubulointerstitium and in segmental deposits within some glomeruli. α₂‐AP^+/+ mice developed crescentic GN (38 ± 9% glomeruli affected) with glomerular fibrin deposition and renal impairment (serum creatinine 30 ± 1 µmol L^?1, normal without GN 11 ± 1 µmol L^?1). Genetic deficiency of α₂‐AP did not result in attenuated glomerular fibrin deposition, crescent formation (39 ± 8% glomeruli affected), glomerular leukocyte infiltration or renal impairment (serum creatinine 33 ± 7 µmol L^?1). α₂‐AP was unmeasurable in kidneys from α₂‐AP^?/? mice, which did not develop compensatory changes in plasminogen, tissue type plasminogen activator (tPA), urokinase type PA (uPA) or plasminogen activator inhibitor‐1 proteins, or changes in tPA or uPA activity. α₂‐AP^?/? mice did have enhanced total renal fibrinolytic capacity as assessed by in situ fibrin overlay (α₂‐AP^+/+ 0.19 ± 0.01, α₂‐AP^?/? 0.36 ± 0.03 lyzed area/total area). Conclusions: α₂‐AP is not important to net glomerular fibrin deposition, crescent formation or renal impairment in crescentic GN.     

Effects of a high‐fat meal on resistance vessel reactivity and on indicators of oxidative stress in healthy volunteers

High fat meals postprandially impair macrovascular endothelial function and a link to increased oxidative stress is suggested. Few information, on the other hand, exists on the effect of postprandial hyperlipidaemia on resistance vessel function. Under normal circumstances this vascular bed regulates tissue perfusion and, by controlling flow, impacts on macrovascular nitric oxide formation. The impact of a high fat meal (1200 kcal, 90 g fat, 46 g protein and 47 g carbohydrates) on postprandial resistance vessel reactivity and on indicators of oxidative stress was studied in 11 healthy subjects by venous‐occlusion plethysmography using another six subjects as time control group. Ingestion of the test meal resulted in a pronounced increase of serum triglycerides from 1·05 ± 0·61 mmol l^?1 in the fasting state to peak postprandial values of 1·94 ± 0·41 mmol l^?1 (P < 0·001) reached after 4 h and a return to baseline after 8 h. Fasting peak reactive hyperaemia (RH) was 19·6 ± 2·4 ml min^?1 (100 ml)^?1. Two hours after ingestion of the test meal peak RH was transiently reduced to 16·8 ± 2·2 ml min^?1 (100 ml)^?1 (P < 0·05). No alteration of resting forearm perfusion was observed. The time course of peak RH suggested a potential biphasic effect of the test meal with an early impairment and a late increase of RH. Ingestion of a lipid rich test meal did not exert any influence on either total plasma antioxidant capacity given in trolox equivalents (513 ± 26 μmol l^?1 at baseline) or on plasma peroxides measured as H₂O₂ equivalents (469 ± 117 μmol l^?1). Our results suggest that ingestion of a meal containing 90 g of fat results in a transient impairment of reactive hyperaemia in healthy subjects but these vascular alterations are not accompanied by signs of systemically increased oxidative stress.     

Influence of glucose and fructose ingestion on the capacity for long-term exercise in well-trained men

Summary. The aim of the present study was to examine the influence of glucose and fructose ingestion on the capacity to perform prolonged heavy exercise. Eight well-trained healthy volunteers exercised on a bicycle ergometer at 68±3% of their VO₂ max until exhaustion, on three occasions, with 8-day intervals. During the exercise they ingested either glucose (250 ml, 7%), fructose (250 ml, 7%) or water (250 ml) every 20 min in a double-blind randomized study design. Arterial blood samples were collected at rest and during exercise for the determination of substrates and hormones. Muscle glycogen content (m. quadriceps femoris) was measured before and after exercise. The duration of exercise lengthened with repeated exercise (3rd test: 136±13 min v. 1st test: 110±12 min, P<0·01). Corrected for the sequence effect, total work time until exhaustion was significantly longer with glucose (137±13 min) than with either fructose (114±12 min) or water (116±13 min) (both P<0·01). When glucose or fructose was ingested, the arterial plasma glucose concentration was maintained at the normoglycaemic level; with water ingestion, plasma glucose values fell during exercise in seven subjects and remained at the resting level in the eighth subject. The muscle glycogen concentration was 467±29 mmol kg d.w.^-1 at rest and fell to approximately half the initial value at exhaustion. In the subgroup of seven subjects in whom glucose values decreased with water intake, the mean rate of glycogen degradation was significantly lower (P<0·05) with the ingestion of glucose (1·3±0·4 mmol kg d.w.^-1 min^-1) as compared to fructose (2·1±0·5 mmol kg d.w.^-1 min^-1) or water (2·3±0·5 mmol kg d.w.^-1 min^-1). Intermittent glucose ingestion (3×17·5 g h^-1) during prolonged, heavy bicycle exercise postpones exhaustion and exerts a glycogen-conserving effect in the working muscles. In contrast, fructose ingestion during exercise maintains the glucose concentration at the basal level but fails to influence either muscle glycogen degradation or endurance performance.     

Postprandial chylomicron and plasma vitamin E responses in healthy older subjects compared with younger ones

The effect of ageing on vitamin E bioavailability in humans was assessed by comparing chylomicron and plasma α-tocopherol postprandial concentrations after a dose of vitamin E (432 or 937 IU as dl-α-tocopherol acetate), in eight young (20–30 years old) and eight healthy elderly men (64–72 years old). The fasting plasma α-tocopherol concentration was significantly higher in the elderly (33 ± 2 μmol L^?1) than in the young (22 ± 2 μmol L^?1). In both groups, the plasma and chylomicron α-tocopherol postprandial concentrations were significantly, approximately twofold, higher after the 937-IU meal than after the 432-IU meal. For both test meals, the chylomicron α-tocopherol areas under the curve were significantly lower in the elderly than in the young subjects: 98.9 ± 16.5 (young group) vs. 55.3 ± 7.8 (elderly group) μmol L^?1 h for the 937-IU test meal and 60.4 ± 14.1 (young group) vs. 26.0 ± 7.6 (elderly group) μmol L^?1 h for the 432-IU test meal, whereas the plasma α-tocopherol area under the curve was significantly higher in elderly than in young subjects: 337.56 ± 16.11 (937-IU test meal) vs. 159.81 ± 35.55 (432-IU test meal) μmol L^?1 h in the young group and 709.55 ± 69.33 (937-IU test meal) vs. 436.39 ± 41.08 (432-IU test meal) μmol L^?1 h in the elderly group. We concluded that (a) the amount of vitamin E appearing in plasma is proportional to the dose ingested (up to 937 IU); (b) the intestinal absorption of vitamin E is not increased, even possibly decreased, in the elderly; and (c) the amount of vitamin E transported by non-chylomicron lipoproteins is apparently higher in the elderly. This suggests that vitamin E postprandial transport is affected by ageing, mainly as the consequence of age-related modifications of lipoprotein metabolism.