Diurnal variations in serum erythropoietin levels in healthy subjects and sleep apnea patients

Pharmacokinetics, Pharmacodynamics, and Safety of Vadadustat in Healthy Volunteers and Patients with Chronic Kidney Disease

Vadadustat is an oral hypoxia-inducible factor prolyl hydroxylase inhibitor for treating anemia in chronic kidney disease (CKD). Single ascending dose (SAD) and multiple ascending dose (MAD) studies assessed pharmacokinetics (PK), pharmacodynamics (PD), and safety of vadadustat in healthy volunteers. A single-dose, open-label study was conducted in patients with CKD stages 3 and 4 not on dialysis. In the SAD study, 48 healthy adult men (n = 8/cohort) received single doses of vadadustat (80-1,200 mg) or placebo. In the MAD study, 34 healthy adult men (n = 8-9/cohort) received daily vadadustat (500-900 mg) or placebo for 10 days. In the single-dose CKD study, 22 male and female patients with CKD (stage 3: n = 10; stage 4: n = 12) received single doses of vadadustat (500 mg). PK parameters included plasma vadadustat; PD biomarkers were measured, including erythropoietin (EPO) levels, reticulocytes, and others. Plasma vadadustat peaked 3-4 hours after single or multiple dosing in healthy volunteers, with a mean t1/2 of approximately 4.5 hours. In patients with CKD, plasma vadadustat peaked at 5-6 hours, with a mean t1/2 of 7.2 (stage 3) and 8.5 (stage 4) hours. Vadadustat AUC∞ and Cmax increased dose proportionally in SAD and MAD trials. In all trials, EPO concentrations increased in a dose-related manner and returned approximately to baseline by 24 hours. Adverse events were mild and considered not study drug related. The PK and PD results of these studies were utilized for further clinical development of vadadustat for treatment of anemia in CKD patients.

The circadian clock regulates rhythmic erythropoietin expression in the murine kidney

Generation of circadian rhythms is cell-autonomous and relies on a transcription/translation feedback loop controlled by a family of circadian clock transcription factor activators including CLOCK, BMAL1 and repressors such as CRY1 and CRY2. The aim of the present study was to examine both the molecular mechanism and the hemopoietic implication of circadian erythropoietin expression. Mutant mice with homozygous deletion of the core circadian clock genes cryptochromes 1 and 2 (Cry-null) were used to elucidate circadian erythropoietin regulation. Wild-type control mice exhibited a significant difference in kidney erythropoietin mRNA expression between circadian times 06 and 18. In parallel, a significantly higher number of erythropoietin-producing cells in the kidney (by RNAscope®) and significantly higher levels of circulating erythropoietin protein (by ELISA) were detected at circadian time 18. Such changes were abolished in Cry-null mice and were independent from oxygen tension, oxygen saturation, or expression of hypoxia-inducible factor 2 alpha, indicating that circadian erythropoietin expression is transcriptionally regulated by CRY1 and CRY2. Reporter gene assays showed that the CLOCK/BMAL1 heterodimer activated an E-box element in the 5' erythropoietin promoter. RNAscope® in situ hybridization confirmed the presence of Bmal1 in erythropoietin-producing cells of the kidney. In Cry-null mice, a significantly reduced number of reticulocytes was found while erythrocyte numbers and hematocrit were unchanged. Thus, circadian erythropoietin regulation in the normoxic adult murine kidney is transcriptionally controlled by master circadian activators CLOCK/BMAL1, and repressors CRY1/CRY2. These findings may have implications for kidney physiology and disease, laboratory diagnostics, and anemia therapy.

Six weeks of dynamic apnoeic training stimulates erythropoiesis but does not increase splenic volume

Purpose

This study examined the influence of dynamic apnoea training on splenic volume and haematological responses in non-breath-hold divers (BHD).

Methods

Eight non-BHD performed ten maximal dynamic apnoeas, four times a week for  six weeks. Splenic volumes were assessed ultrasonically, and blood samples were drawn for full blood count analysis, erythropoietin, iron, ferritin, albumin, protein and osmolality at baseline, 24 h post the completion of each week’s training sessions and seven days post the completion of the training programme. Additionally, blood samples were drawn for haematology at 30, 90, and 180 min post session one, twelve and twenty-four.

Results

Erythropoietin was only higher than baseline (6.62 ± 3.03 mlU/mL) post session one, at 90 (9.20 ± 1.88 mlU/mL, p = 0.048) and 180 min (9.04 ± 2.35 mlU/mL, p = 0.046). Iron increased from baseline (18 ± 3 µmol/L) post week five (23 ± 2 µmol/L, p = 0.033) and six (21 ± 6 µmol/L; p = 0.041), whereas ferritin was observed to be lower than baseline (111 ± 82 µg/L) post week five (95 ± 75 µg/L; p = 0.016), six (84 ± 74 µg/L; p = 0.012) and one week post-training (81 ± 63 µg/L; p = 0.008). Reticulocytes increased from baseline (57 ± 12 × 10⁹/L) post week one (72 ± 17 × 10⁹/L, p = 0.037) and six (71 ± 17 × 10⁹/L, p = 0.021) while no changes were recorded in erythrocytes (p = 0.336), haemoglobin (p = 0.124) and splenic volumes (p = 0.357).

Conclusions

Six weeks of dynamic apnoeic training increase reticulocytes without altering mature erythrocyte concentration and splenic volume.

Erythropoietic responses to a series of repeated maximal dynamic and static apnoeas in elite and non-breath-hold divers

Purpose

Serum erythropoietin (EPO) concentration is increased following static apnoea-induced hypoxia. However, the acute erythropoietic responses to a series of dynamic apnoeas in non-divers (ND) or elite breath-hold divers (EBHD) are unknown.

Methods

Participants were stratified into EBHD (n = 8), ND (n = 10) and control (n = 8) groups. On two separate occasions, EBHD and ND performed a series of five maximal dynamic apnoeas (DYN) or two sets of five maximal static apnoeas (STA). Control performed a static eupnoeic (STE) protocol to control against any effects of water immersion and diurnal variation on EPO. Peripheral oxygen saturation (SpO₂) levels were monitored up to 30 s post each maximal effort. Blood samples were collected at 30, 90, and 180 min after each protocol for EPO, haemoglobin and haematocrit concentrations.

Results

No between group differences were observed at baseline (p > 0.05). For EBHD and ND, mean end-apnoea SpO₂ was lower in DYN (EBHD, 62 ± 10%, p = 0.024; ND, 85 ± 6%; p = 0.020) than STA (EBHD, 76 ± 7%; ND, 96 ± 1%) and control (98 ± 1%) protocols. EBHD attained lower end-apnoeic SpO₂ during DYN and STA than ND (p < 0.001). Serum EPO increased from baseline following the DYN protocol in EBHD only (EBHD, p < 0.001; ND, p = 0.622). EBHD EPO increased from baseline (6.85 ± 0.9mlU/mL) by 60% at 30 min (10.82 ± 2.5mlU/mL, p = 0.017) and 63% at 180 min (10.87 ± 2.1mlU/mL, p = 0.024). Serum EPO did not change after the STA (EBHD, p = 0.534; ND, p = 0.850) and STE (p = 0.056) protocols. There was a significant negative correlation (r = − 0.49, p = 0.003) between end-apnoeic SpO₂ and peak post-apnoeic serum EPO concentrations.

Conclusions

The novel findings demonstrate that circulating EPO is only increased after DYN in EBHD. This may relate to the greater hypoxemia achieved by EBHD during the DYN.

Effects of intermittent hypoxic training performed at high hypoxia level on exercise performance in highly trained runners

This study exanimated the effects of intermittent hypoxic training (IHT) conducted at a high level of hypoxia with recovery at ambient air on aerobic/anaerobic capacities at sea level and hematological variations. According to a double-blind randomized design, fifteen highly endurance-trained runners completed a 6-weeks regimented training with 3 sessions per week consisting of intermittent runs (6x work-rest ratio of 5':5') on a treadmill at 80-85% of maximal aerobic speed ([Formula: see text]). Nine athletes (hypoxic group, HG) performed the exercise bouts at FI0₂ = 10.6-11.4% while six athletes (normoxic group, NG) exercised at ambient air. Running time to exhaustion at a velocity corresponding to 95% [Formula: see text] significantly increased for HG while no effect was found for NG. Regarding [Formula: see text], no significant effects were found in either training group. In addition, the decline of jumping performances over a 45s-continuous maximal vertical jump test (i.e. anaerobic capacity index) tended to be lower in HG compared to NG. The levels of the studied hematological variables, including erythropoietin and hematocrit, did not significantly change for either HG or NG. These results highlight that our IHT protocol may induce additional effects on aerobic performance without compromising the anaerobic capacity index in highly-trained athletes.

Increased Urinary Erythropoietin Excretion in Severe Sleep Apnea-Hipoapnea Syndrome: The Effect of CPAP

INTRODUCTION

Tissue hypoxia stimulates the production of erythropoietin (EPO), the main effect of which is, in turn, to stimulate erythropoiesis. Sleep apnea-hypopnea syndrome (SAHS) is an entity characterized by repeated episodes of hypoxemia during sleep.

OBJECTIVE

To analyze whether hypoxemia stimulated increased urinary excretion of EPO, and if so, to evaluate if treatment with continuous positive airway pressure (CPAP) can inhibit this phenomenon.

METHODS

We studied 25 subjects with suspected SAHS who underwent a polysomnography study (PSG). EPO levels in first morning urine (uEPO) and blood creatinine and hemoglobin were determined in all patients. Patients with severe SAHS repeated the same determinations after CPAP treatment.

RESULTS

Twelve subjects were diagnosed with severe SAHS (mean ± SD, AHI 53.1 ± 22.7). Creatinine and hemoglobin levels were normal in all subjects. uEPO was 4 times higher in the SAHS group than in the control group (1.32 ± 0.83 vs. 0.32 ± 0.35 UI/l, p <.002). CPAP treatment reduced uEPO to 0.61 ± 0.9 UI/l (p <.02), levels close to those observed in healthy subjects. No dose-response relationship was observed between severity of PSG changes and uEPO values.

CONCLUSIONS

Patients with severe SAHS show increased uEPO excretion, but this normalizes after treatment with CPAP.

Diurnal changes of arterial oxygen saturation and erythropoietin concentration in male and female highlanders

In Caucasians and Native Americans living at altitude, hemoglobin mass is increased in spite of erythropoietin concentrations ([Epo]) not markedly differing from sea level values. We hypothesized that a nocturnal decrease of arterial oxygen saturation (SaO₂) causes a temporary rise of [Epo] not detected by morning measurements. SaO₂ (continuous, finger oximeter) and [Epo] (ELISA, every 4 h) were determined in young highlanders (altitude 2600 m) during 24 h of usual daily activity. In Series I (six male, nine female students), SaO₂ fell during the night with the nadir occurring between 01:00 and 03:00; daily means (range 92.4–95.2%) were higher in females (+1.7%, P < 0.01). [Epo] showed opposite changes with zenith occurring at 04:00 without a sex difference. Mean daily values (22.9 ± 10.7SD U/L) were higher than values obtained at 08:00 (17.2 ± 9.5 U/L, P < 0.05). In Series II (seven females), only SaO₂ was measured. During follicular and luteal phases, SaO₂ variation was similar to Series I, but the rhythm was disturbed during menstruation. While daily [Epo] variations at sea level are not homogeneous, there is a diurnal variation at altitude following changes in SaO₂. Larger hypoventilation‐dependent decreases of alveolar PO₂ decreases during the night probably cause a stronger reduction of SaO₂ in highlanders compared to lowlanders. This variation might be enlarged by a diurnal fluctuation of Hb concentration. In spite of a lower [Hb], the higher SaO₂ in women compared to men led to a similar arterial oxygen content, likely explaining the absence of differences in [Epo] between sexes.

Early predictors of neonatal intraventricular hemorrhage

OBJECTIVE

Current study aimed toward the early prediction of neonatal intraventricular hemorrhage (IVH) for better management and prognosis.

METHODS

This prospective study was conducted on forty neonates at the Neonatal Intensive Care Unit of Pediatrics and Medical Biochemistry department (Tanta University, Egypt) from July 2016 to June 2017. Cord blood erythropoietin and venous blood Activin A were assayed within the first hour of life. Neonates were divided into 2 groups: Group 1 (with IVH) included twenty neonates who developed IVH proved by transcranial ultrasonography (u/s) and Group 2 (without IVH) included twenty neonates who were admitted to the NICU but did not develop IVH, also proved by transcranial u/s. Data were analyzed using Chi Square and t-test.

RESULTS

Group 1 had a significantly higher cord blood erythropoietin concentration than group 2 (46.75±27.98 mIU/mL vs. 18.82±8.91 mIU/mL), respectively (p<0.05). Group 1 had a significantly higher venous blood Activin A concentration than group 2 (3.18±2 ng/L vs. 0.42±0.25 ng/L) with (p<0.05).

CONCLUSION

Cord blood erythropoietin and venous blood Activin A were presumed to be used as early predictors of IVH in neonates with early treatment and better prognosis.

Erythropoietin levels in patients with sleep apnea: a meta-analysis

Currently available data regarding the blood levels of erythropoietin (EPO) in sleep apnea (SA) patients are contradictory. The aim of the present meta-analysis was to evaluate the EPO levels in SA patients via quantitative analysis. A systematic search of Pubmed, Embase, and Web of Science were performed. EPO levels in SA group and control group were extracted from each eligible study. Weight mean difference (WMD) or Standard mean difference (SMD) with 95% confidence interval (CI) was calculated by using fixed-effects or random effect model analysis according to the degree of heterogeneity between studies. A total of 9 studies involving 407 participants were enrolled. The results indicated that EPO levels in SA group were significantly higher than that in control group (SMD 0.61, 95% CI 0.11–1.11, p = 0.016). Significantly higher EPO levels were found in patients with body mass index <30 kg/m², and cardiovascular complications in the subsequent subgroup analysis (both p < 0.05). High blood EPO levels were found in SA patients in the present meta-analysis.

Blood biomarkers of endocrine, immune, inflammatory, and metabolic systems in obstructive sleep apnea

OBJECTIVE/BACKGROUND

Obstructive sleep apnea (OSA) is a common disorder, affecting over 100 million adults. Untreated OSA leads to serious health consequences and perturbations in endocrine, immune, inflammatory, and metabolic systems. Study objectives are to evaluate the association between OSA and biomarkers, and to test the hypothesis that a combination of markers may be useful in screening for OSA.

PATIENTS/METHODS

A multicenter trial was conducted enrolling symptomatic male patients with suspected OSA. All subjects underwent in-laboratory overnight polysomnography. A non-symptomatic control group was also obtained. Eleven biomarkers were tested: HbA1c, CRP, EPO, IL-6, uric acid, cortisol, hGH, prolactin, testosterone, DHEA (Beckman Coulter UniCel DxC 600i Synchron® Access® Clinical Systems), IGF-1.

RESULTS

73 male subjects were enrolled; 26 had moderate/severe OSA. ROC curve analysis showed HbA1c, CRP, EPO, IL-6, and Uric Acid (AUCs: 0.76, 0.73, 0.65, 0.65, 0.61) were superior to the Epworth Sleepiness Scale (AUC: 0.52). Concurrent elevation of HbA1c and CRP provide even greater predictive power. A combination of elevated HbA1c, CRP, and EPO provided 0.08 increase in AUC (0.84 [0.75 - 0.94]) over individual markers (p<0.05), with high sensitivity (85%), and specificity (79%) for moderate/severe OSA.

CONCLUSIONS

OSA induces characteristic endocrine, immune, inflammatory, and metabolic disturbances that can be detected with blood biomarkers. These biomarkers are superior to standard screening questionnaires. Various clusters of these biomarkers have an even greater association with OSA and thus may represent physiologic signatures of the disorder that may have value in initial screening for OSA as well as for follow-up of therapy response.

The impact of chronic intermittent hypoxia on hematopoiesis and the bone marrow microenvironment

Obstructive sleep apnea (OSA) is a highly prevalent sleep-related breathing disorder which is associated with patient morbidity and an elevated risk of developing hypertension and cardiovascular diseases. There is ample evidence for the involvement of bone marrow (BM) cells in the pathophysiology of cardiovascular diseases but a connection between OSA and modulation of the BM microenvironment had not been established. Here, we studied how chronic intermittent hypoxia (CIH) affected hematopoiesis and the BM microenvironment, in a rat model of OSA. We show that CIH followed by normoxia increases the bone marrow hypoxic area, increases the number of multipotent hematopoietic progenitors (CFU assay), promotes erythropoiesis, and increases monocyte counts. In the BM microenvironment of CIH-subjected animals, the number of VE-cadherin-expressing blood vessels, particularly sinusoids, increased, accompanied by increased smooth muscle cell coverage, while vWF-positive vessels decreased. Molecularly, we investigated the expression of endothelial cell-derived genes (angiocrine factors) that could explain the cellular phenotypes. Accordingly, we observed an increase in colony-stimulating factor 1, vascular endothelium growth factor, delta-like 4, and angiopoietin-1 expression. Our data shows that CIH induces vascular remodeling in the BM microenvironment, which modulates hematopoiesis, increasing erythropoiesis, and circulating monocytes. Our study reveals for the first time the effect of CIH in hematopoiesis and suggests that hematopoietic changes may occur in OSA patients.

Pharmacokinetic and Pharmacodynamic Comparison of Two Recombinant Human Erythropoietin Formulations, PDA10 and Eprex, in Healthy Korean Male Volunteers: A Randomized, Double-Blinded, Single-Dose, Two-Period Crossover Study

BACKGROUND AND OBJECTIVES

A new biosimilar human recombinant epoetin alfa product (PDA10) has been developed by PanGen Biotech Inc., Korea. This study was planned to demonstrate the pharmacokinetic and pharmacodynamic comparability of PDA10 to an existing epoetin alfa (Eprex) after a single intravenous administration to healthy adult male volunteers.

METHODS

A randomized, double-blinded, single-dose, crossover study was conducted in 30 subjects. The subjects were assigned randomly to one of two sequence groups, and single doses of 100 IU/kg PDA10 or Eprex were administered intravenously on each of 2 treatment days separated by a 4-week washout period. Plasma erythropoietin concentrations were measured using an enzyme-linked immunosorbent assay and the pharmacokinetic parameters of the two treatments were compared. The time course and area under the effect curve (AUEC) of absolute reticulocyte counts were used as surrogate parameters for the pharmacodynamic evaluation. Adverse events (AEs) were recorded.

RESULTS

A total of 30 subjects were enrolled, and 27 completed the study. The geometric mean ratios (PDA10/Eprex) of erythropoietin for maximum plasma concentration (C max) and area under the plasma concentration-time curve to the last measurable concentration (AUC0-last) after intravenous administration of 100 IU/kg were 1.00 (90% confidence interval [CI] 0.96-1.05) and 0.96 (90% CI 0.93-1.00). The absolute reticulocyte counts of PDA10 and Eprex were similar, as determined from the maximum reticulocyte count and AUEC0-last values. Treatment-emergent AEs were mild and occurred in seven subjects.

CONCLUSION

PDA10 and Eprex met the regulatory criteria for bioequivalence with respect to their pharmacokinetic profiles and pharmacodynamic actions.

OSA and pulmonary hypertension: time for a new look

OSA is a common yet underdiagnosed disorder encountered in everyday practice. The disease is a unique physiologic stressor that contributes to the development or progression of many other disorders, particularly cardiovascular conditions. The pulmonary circulation is specifically affected by the intermittent hypoxic apneas associated with OSA. The general consensus has been that OSA is associated with pulmonary hypertension (PH), but only in a minority of OSA patients and generally of a mild degree. Consequently, there has been no sense of urgency to screen for either condition when evaluating the other. In this review, we explore available evidence describing the interaction between OSA and PH and seek to better understand underlying pathophysiology. We describe certain groups of patients who have a particular preponderance of OSA and PH. Failure to recognize the mutual additive effects of these disorders can lead to suboptimal patient outcomes. Among patients with PH and OSA, CPAP, the mainstay treatment for OSA, may ameliorate pulmonary pressure elevations, but has not been studied adequately. Conversely, among patients with OSA, PH significantly limits functional capacity and potentially shortens survival; yet, there is no routine screening for PH in patients with OSA. We think it is time to study the interaction between OSA and PH more carefully to identify high-risk subgroups. These would be screened for the presence of combined disorders, facilitating earlier institution of therapy and improving outcomes.

Reticulocytes in sports medicine: an update

Reticulocytes are young red blood cells which develop from erythroblasts and circulate in the bloodstream for about 1-4 days before maturing into erythrocytes. With the introduction of reticulocyte count in equations and statistical models for detecting suspected blood doping, its application to sports medicine has attracted growing interest in reticulocyte behavior during training and competition seasons in athletes and experimental blood doping treatment in healthy volunteers. An update on recent publications is therefore needed to improve the interpretation of reticulocyte analysis and its variability in sportsmen. Reticulocyte count constitutes a robust parameter during the preanalytical phase, but cell stability can be assured only if blood samples are kept at constantly cold temperatures (4 degrees C) and test results will differ depending on the blood analyzer system used. Marked intraindividual variability is the principal finding to be evaluated when exercise-induced changes are observed or illicit procedures suspected. Furthermore, reticulocyte variability is greater than that of other hematological parameters such as hemoglobin or hematocrit. Ideally, any variation should be interpreted against long-term time series for the individual athlete: values obtained from large athlete cohorts ought to be used only for extrapolating outliers that deserve further examination. Reticulocyte distribution in athletes is similar to that found in the general population, and a gender effect in some sports disciplines or selected athlete groups may be seen. Reticulocyte variability is strongly influenced by seasonal factors linked to training and competition schedules and by the type of sports discipline. Published experimental data have confirmed the high sensitivity of reticulocyte analysis in identifying abnormal bone marrow stimulation by either erythropoietin administration or blood withdrawal and reinfusion.

Long-term intermittent hyperoxic exposures do not enhance erythropoiesis

BACKGROUND

Based on a report of a marked increase in the erythropoietin concentration ([EPO]) a few hours after the cessation of a single 2-h session of O(2) breathing, short periods of O(2) administration have been advocated as a therapy for anaemia. Accordingly, the purpose of the present study was to evaluate this theory by investigating the effect of 10 daily short-term exposures to normobaric O(2) over a 2-week period on the plasma [EPO] in healthy individuals.

MATERIAL AND METHODS

Twenty men were assigned to either an experimental (NBO(2)) or to a control (AIR) group. The NBO(2) group breathed 100% normobaric O(2) for 2 h every weekday over a 2-week period. The AIR group breathed air within the same time protocol. Blood samples were collected at the pre-, mid- and post-intervention periods to determine [EPO].

RESULTS

[EPO] of the NBO(2) group was significantly lower than that of the AIR group during the mid- and post-periods (P < 0·001). [EPO] of the NBO(2) group showed a slight, albeit statistically nonsignificant, decrease during the mid (∼11%)- and post (∼16%)-periods.

CONCLUSIONS

Daily short-term exposures to normobaric hyperoxia do not increase the [EPO] in healthy individuals. The increased O(2) tension suppresses [EPO]. Hence, administration of pure O(2) to enhance erythropoiesis is not warranted.

Acute normobaric hyperoxia transiently attenuates plasma erythropoietin concentration in healthy males: evidence against the 'normobaric oxygen paradox' theory

AIM

The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O(2) exposure on the concentration of plasma erythropoietin (EPO).

METHODS

Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O(2) (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96 h, and 1 and 2 weeks after the exposure to determine EPO concentration.

RESULTS

The concentration of plasma erythropoietin increased markedly 8 and 32 h after the NOR exposure (approx. 58% and approx. 52%, respectively, P ≤ 0.05) as a consequence of its natural diurnal variation. Conversely, the O(2) breathing was followed by approx. 36% decrement of EPO 3 h after the exposure (P ≤ 0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8 h after the breathing intervention (P ≤ 0.05).

CONCLUSION

In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O(2) breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O(2) tension suppresses the EPO concentration 3 and 5 h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation.

Reticulocytes in sports medicine

Reticulocytes are the transitional cells from erythroblasts to mature erythrocytes. Reticulocytes are present in blood for a period of 1-4 days and can be recognized by staining with supravital dyes, such as new methylene blue, or fluorescent markers, which couple residual nucleic acid molecules, a hallmark of the immature forms of erythrocytes. Although reticulocytes could be counted through a microscope (there is a standard of International Committee for Standardisation in Haematology for manual counting), this method is reported to be time consuming, inaccurate and imprecise. The integration of the reticulocyte count in automated haematology systems allowed the widespread use of these parameters, although the lack of calibration material and different markers, technologies and software used in automated systems could engender discrepancies among data obtained from different analytical systems.The importance of reticulocytes in sports medicine derives from their sensitivity, the highest among haematology parameters, in identifying the bone marrow stimulation, especially when recombinant human erythropoietin is fraudulently used. Automated systems are also able to supply information on volume, density and the haemoglobin content of reticulocytes. Some of the related parameters are also used in algorithms for identifying abnormal stimulation of bone marrow as reticulocytes haematocrit. The pre-analytical variability of reticulocytes (transportation, storage, biological variability) should be taken into account in sports medicine also. Reticulocytes remain stable for almost 24 hours at 4 degrees C from blood drawing, they are affected by transportation, and biological variability is not high in general. It could be remarked, however, that the intra-individual variability is high when compared with other haematological parameters such as haemoglobin and haematocrit. The intervals of data reported in athletes are very similar to reference intervals characterizing the general population.The reticulocyte count shows some modifications after training and during the competition season. The variability induced by exercise cannot be overlooked since the so-called haematological passport, a personal athlete's document in which haemoglobin and other parameters are registered, may be introduced by sports federations. Exposure to naturally high altitude and 'living high-training low' programmes determined contentious results on reticulocytes. Simulated high altitude induced by intermittent hypobaric hypoxia does not modify reticulocytes, despite an increase in erythropoietin serum concentration. The variability among athletes competing in different sport disciplines is apparently limited. The knowledge of the behaviour of reticulocytes in training and competitions is crucial for defining their role in an antidoping control context. It is important for sport physicians and clinical pathologists to know the reticulocyte variability in the general population and in athletes, the pre-analytical warnings, the different methodologies for counting reticulocytes and the derived parameters automatically available, and, finally, the possible influence of training, competitions, type of sport and altitude.

Iron and anemia in human biology: a review of mechanisms

The biology of iron in relation to anemia is best understood by a review of the iron cycle, since the majority of iron for erythropoiesis is provided by iron recovered from senescent erythrocytes. In iron-deficiency anemia, storage iron declines until iron delivery to the bone marrow is insufficient for erythropoiesis. This can be monitored with clinical indicators, beginning with low plasma ferritin, followed by decreased plasma iron and transferrin saturation, and culminating in red blood cells with low-Hb content. When adequate dietary iron is provided, these markers show return to normal, indicating a response to the dietary supplement. Anemia of inflammation (also known as anemia of chronic disease, or ACD) follows a different course, because in this form of anemia storage iron is often abundant but not available for erythropoiesis. The diagnosis of ACD is more difficult than the diagnosis of iron-deficiency anemia, and often the first identified symptom is the failure to show a response to a dietary iron supplement. Confirmation of ACD is best obtained from elevated markers of inflammation. The treatment of ACD, which typically employs erythropoietin (EPO) supplements and intravenous iron (i.v.-iron), is empirical and often falls shorts of therapeutic goals. Dialysis patients show a complex pattern of anemia, which results from inadequate EPO production by the kidney, inflammation, changes in nutrition, and blood losses during treatment. EPO and i.v.-iron are the mainstays of treatment. Patients with heart failure can be anemic, with incidence as high as 50%. The causes are multifactorial; inflammation now appears to be the primary cause of this form of anemia, with contributions from increased plasma volume, effects of drug therapy, and other complications of heart disease. Discerning the mechanisms of anemia for the heart failure patient may aid rational therapy in each case.

Increased erythrocyte adhesiveness and aggregation in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea (OSA) is associated with an increased incidence of stroke and myocardial infarction as well as increased prothrombotic and inflammatory processes. Although erythrocyte adhesiveness/aggregation is known to be elevated in cardiovascular diseases, it has never been evaluated in OSA. The aim of this study was to examine the possible association of OSA and erythrocyte adhesiveness/aggregation.

METHODS

The study was conducted in the Sleep Laboratory of a tertiary university-affiliated medical center in 79 patients (age 57.1+/-12.9 years) with a diagnosis of OSA (apnea hypopnea index 41.2+/-25.9). Findings were compared with data on 1079 controls without clinical symptoms of OSA, matched for sex, age, and body mass index. Overnight polysomnography and blood sampling for erythrocyte sedimentation rate, levels of fibrinogen, high-sensitivity C-reactive protein, and erythrocyte adhesion/aggregation test consisting of measures of erythrocyte percentage and vacuum range on image analysis.

RESULTS

The study group had significantly higher values than controls of all three markers of inflammation (p<0.001 for erythrocyte sedimentation rate and fibrinogen; p=0.037 for C-reactive protein). Erythrocyte percentage was significantly lower in the sleep apnea group (84.05+/-15.97 vs. 90.79+/-11.23%, p<0.001), and vacuum range was significantly higher (8.22+/-7.98 vs. 4.63+/-4.05 microm, p<0.001), indicating stronger erythrocyte adhesion/aggregation. Both these factors were significantly correlated with erythrocyte sedimentation rate and to hs-CRP (percentage: r=-0.630; 0.258, p=0.005; 0.031; vacuum range: r=0.494; -0.328, p=0.001; 0.005 respectively).

CONCLUSION

OSA is associated with increased erythrocyte aggregation/adhesion, which is correlated with an increase in inflammation markers. These findings might help explain the increased cardiovascular morbidity in OSA.

Does obstructive sleep apnea increase hematocrit?

This study assessed the relationship between hematocrit levels and severity of obstructive sleep apnea (OSA) and examined how this relationship was affected by the degree of hypoxia as well as by possible confounding factors. Two-hundred sixty three subjects (189 men and 74 women) underwent nocturnal polysomnography with oximetry and had measurements of hematocrit, hemoglobin, white blood cell count, body mass index (BMI), blood pressure (BP), and 24-h urine norepinephrine (NE). Patients with severe OSA [respiratory disturbance index (RDI) >30] had significantly higher hematocrit values than patients with mild to moderate OSA or nonapneic controls (p < 0.01). However, only one patient had a hematocrit in the range of clinical polycythemia. Hematocrit levels were significantly correlated with BMI, BP, urinary NE, RDI, percent of time spent at oxygen saturation <90%, and with mean oxygen saturation. Multiple linear regression analysis revealed that mean oxygen saturation, RDI, and percent of time spent at oxygen saturation <90% were significant predictors of hematocrit level, even after controlling for gender, ethnicity, 24-h urine NE, BMI, and BP (p < 0.05). The severity of OSA is significantly associated with increased hematocrit, even after controlling for possible confounding variables. However, nocturnal hypoxemia in OSA does not usually lead to clinical polycythemia.

Ca2+/calmodulin kinase-dependent activation of hypoxia inducible factor 1 transcriptional activity in cells subjected to intermittent hypoxia

Intermittent hypoxia (IH) occurs in many pathological conditions. However, very little is known about the molecular mechanisms associated with IH. Hypoxia-inducible factor 1 (HIF-1) mediates transcriptional responses to continuous hypoxia. In the present study, we investigated whether IH activates HIF-1 and, if so, which signaling pathways are involved. PC12 cells were exposed to either to 20% O2 (non-hypoxic control) or to 60 cycles consisting of 30 s at 1.5% O2, followed by 4 min at 20% O2 (IH). Western blot analysis revealed significant increases in HIF-1alpha protein in nuclear extracts of cells subjected to IH. Expression of a HIF-1-dependent reporter gene was increased 3-fold in cells subjected to IH. Although IH induced the activation of ERK1, ERK2, JNK, PKC-alpha, and PKC-gamma, inhibitors of these kinases and of phosphatidylinositol 3-kinase did not block HIF-1-mediated reporter gene expression induced by IH, indicating that signaling via these kinases was not required. In contrast, addition of the intracellular Ca2+ chelator BAPTA-AM or the Ca2+/calmodulin-dependent (CaM) kinase inhibitor KN93 blocked reporter gene activation in response to IH. CaM kinase activity was increased 5-fold in cells subjected to IH. KN 93 prevented IH-induced transactivation mediated by HIF-1alpha, and its coactivator p300, which was phosphorylated by CaM kinase II in vitro. Expression of the HIF-1-regulated gene encoding tyrosine hydroxylase was induced by IH and this effect was blocked by KN93. These observations suggest that IH induces HIF-1 transcriptional activity via a novel signaling pathway involving CaM kinase.

Intracerebroventricular injection of erythropoietin enhances sleep in the rat

Systemic injection of erythropoietin (EPO) over several days reduces sleep fragmentation in patients with periodic limb movements in sleep (PLMS). However, there are no studies concerning the effects of EPO on spontaneous sleep. In this study, we determined the effects of intracerebroventricular (i.c.v.) administration of EPO on spontaneous rat sleep. Three doses of EPO (25, 75, and 125 ng) were injected i.c.v. at the onset of the dark period. All doses of EPO increased non-rapid eye movement sleep (NREMS). In addition, high and low doses of EPO (125 and 25 ng) increased rapid eye movement sleep (REMS), but the medium dose of EPO (75 ng) inhibited REMS. Electroencephalogram slow-wave activity during NREMS also increased following the two higher doses of EPO. In contrast, EPO injection during the light period failed to affect sleep. Brain temperature (Tbr) was not affected by any dose of EPO. These results suggest that EPO could be part of the cytokine network involved in sleep regulation.

Obstructive sleep apnoea syndrome--an oxidative stress disorder

Obstructive sleep apnoea syndrome (OSA) is associated with increased cardiovascular morbidity and mortality. However, the underlying mechanisms are not entirely understood. This review will summarize the evidence that substantiates the notion that the repeated apnoea-related hypoxic events in OSA, similarly to hypoxia/reperfusion injury, initiate oxidative stress. Thus, affecting energy metabolism, redox-sensitive gene expression, and expression of adhesion molecules. A limited number of studies substantiate this hypothesis directly by demonstrating increased free radical production in OSA leukocytes and increased plasma-lipid peroxidation. A great number of studies, however, support this hypothesis indirectly. Increase in circulating levels of adenosine and urinary uric acid in OSA are implicated with increased production of reactive oxygen species (ROS). Activation of redox-sensitive gene expression is suggested by the increase in some protein products of these genes, including VEGF, erythropoietin, endothelin-1, inflammatory cytokines and adhesion molecules. These implicate the participation of redox-sensitive transcription factors as HIF-1 AP-1 and NFkappaB. Finally, adhesion molecule-dependent increased avidity of OSA monocytes to endothelial cells, combined with diminished NO bioavailability, lead to exaggerated endothelial cell damage and dysfunction. Cumulatively, these processes may exacerbate atherogenic sequelae in OSA.

Sleep disorders and the failure to lower nocturnal blood pressure

PURPOSE OF REVIEW

The failure to lower systolic blood pressure at night (called non-dipping) and sleep apnea are both associated with adverse cardiovascular outcomes. Sleep apnea is a common cause of non-dipping blood pressure.

RECENT FINDINGS

Sleep apnea increases night time blood pressure through enhanced cardiac pre-load, sleep disturbance and hypoxia. Hypoxia elicits increased levels of norepinephrine, endothelin and erythropoetin. Patients with sleep apnea tend to be elderly and obese, so they have poor endothelial nitric oxide release and blunted baroreflexes. They thus have several stimuli for high blood pressure and poor compensatory mechanisms to lower blood pressure.

SUMMARY

Non-dipping patients without sleep apnea have evidence of volume overload and correct their blood pressure pattern in response to diuretics. Individuals with sleep apnea have evidence of increased cardiac pre-load from episodes of negative intrathoracic pressure. Their daytime blood pressure responds poorly to many drugs, but beta blockers may be effective. Their night time blood pressure responds only slightly to therapy of their sleep apnea with continuous positive airway pressure, even though continuous positive airway pressure decreases their norepinephrine, erythropoetin and endothelin levels.

Effects of intermittent exposure to high altitude on blood volume and erythropoietic activity

The purpose of this review is to describe changes in blood volume and erythropoietic activity occurring under different types of intermittent exposure to hypoxia. These hypoxic episodes can vary from a few seconds or minutes to hours, days, or even weeks. Short hypoxic episodes like sleep apnea only lead to a small increase in hemoglobin concentration, which is mainly due to a hormonal-mediated decrease in plasma volume. In most of these cases the cumulative time spent under hypoxia does not exceed the critical threshold of about 90 min. Endurance athletes and mountaineers who voluntarily expose themselves to hypoxia for some hours or during the night while spending the day at normoxia ("sleep high-train low" concept) do improve their physical performance. Despite raising erythropoietic activity, indicated by elevated plasma concentrations of EPO and the transferrin receptor, the postulated increase in red cell volume has not satisfactorily been proved. Frequent changes between low and high altitudes, which are usual in some South American and Asian countries, provoke similar adaptations in red cell mass as occur in high altitude residents. However, the plasma volume decreases at altitude and increases again when staying at sea level. Even after more than 20 yr of regular moving between low and high altitude, the total blood volume, hemoglobin concentration and hematocrit, as well as the plasma EPO concentration, noticeably oscillate during every hypoxic-normoxic cycle. We assume these changes to be an optimal rapid adaptation of the oxygen transport system to the prevailing hypoxic or normoxic environment. However, possible risks for the organism cannot be excluded.

Haematological aspects of obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is associated with increased cardiovascular morbidity and mortality. Several studies indicate an influence of OSA on haematological features. There is evidence of elevated platelet activation and increased haematocrit in OSA. Studies investigating the underlying cause of polycythaemia in OSA reveal different results: increased haematocrit in OSA might be due to enhanced erythropoietin excretion and/or plasma volume dysregulation based on altered release of volume-regulating hormones such as atrial natriuretic peptide (ANP). This review addresses haematological issues associated with OSA, especially platelet function, haematocrit and haemoconcentration. 2001 Harcourt Publishers Ltd

Chronic intermittent hypoxia increases haematocrit and causes right ventricular hypertrophy in the rat

Chronic continuous hypoxia increases haematocrit and causes right ventricular hypertrophy and pulmonary hypertension. In obstructive sleep apnoea, the exposure to hypoxia is intermittent rather than continuous but the effects of chronic intermittent hypoxia on haematocrit and right ventricular mass are unclear. Wistar rats were exposed to alternating periods of hypoxia and normoxia twice per min for 8 h per day for 5 weeks in order to mimic the intermittent hypoxia of obstructive sleep apnoea in humans. Haematocrit was significantly raised at day 7, 14, 21, 28 and 35 of the treatment period. At the end of the treatment, there was a significant increase in right ventricular mass. Therefore, chronic intermittent hypoxia increases haematocrit and right heart mass. These results suggest that the raised haematocrit and pulmonary arterial pressure observed in some cases of obstructive sleep apnoea in humans may be caused by intermittent nocturnal hypoxaemia.

Human milk as a potential enteral source of erythropoietin

In addition to its content of traditional nutrients, milk is a rich source of hormones and peptides, which survive digestion in the neonatal gastrointestinal tract secondary to lower proteolytic activity and increased protein permeability. Previous studies have shown accelerated erythropoiesis or elevated serum erythropoietin (Epo) levels in neonatal (suckling) animals after maternal phlebotomy or maternal hypoxia exposure. We sought to determine whether significant quantities of Epo are present in human milk and whether Epo remains intact under physiologic digestion conditions. Immunoreactive Epo concentrations were determined in 409 human milk samples obtained from mothers of term and premature infants. Samples collected between birth and postpartum d 134 were divided into 11 postpartum day groups. Mean milk-borne Epo concentrations were within the normal range for plasma Epo concentrations and rose with postpartum day (F10,398 = 5.82, p < 0.0001). No differences were observed between milk collected from mothers of premature versus term infants. Estimated weekly human milk-borne Epo intakes approximated the lower range of published parenteral therapeutic doses. In simulated digestion at physiologic pH levels of 3.2, 5.8, and 7.4, milk-borne Epo resisted degradation at 1 and 2 h, compared with baseline. Therefore, we conclude that human milk contains considerable amounts of Epo which resist degradation after exposure to gastric juices at physiologic pH levels. These results support continued investigation into the fate and developmental roles of Epo in human milk.

Preanalytical factors and the measurement of cytokines in human subjects

Cytokines are widely measured in research. However, cytokine analyses are influenced by a myriad of factors. For instance, a delay in the separation of plasma from cells may lead to a 50% decrease in the concentration of tumor necrosis factor in plasma. Another example is the secretion of interleukin-1 beta in women which can be twice as high during the follicular phase as in the luteal phase. The factors influencing the outcome of these tests can be divided into in vivo preanalytical factors (e.g., aging, chronobiological rhythms, diet, etc), in vitro preanalytical factors (e.g., specimen collection, equipment, transport, storage, etc), and analytical factors. To improve the value of the cytokine tests, factors strongly influencing the results have to be controlled. This can be done by using standardized assays and specimen collection procedures. In general, sufficient attention is not given to the preanalytical factors, especially in the measurement of cytokines. This article reviews the preanalytical factors which may influence the outcome of these tests in human subjects.

Diurnal variations of serum erythropoietin at sea level and altitude

This study tested the hypothesis that the diurnal variations of serum-erythropoietin concentration (serum-EPO) observed in normoxia also exist in hypoxia. The study also attempted to investigate the regulation of EPO production during sustained hypoxia. Nine subjects were investigated at sea level and during 4 days at an altitude of 4350 m. Median sea level serum-EPO concentration was 6 (range 6-13) U.l-1. Serum-EPO concentration increased after 18 and 42 h at altitude, [58 (range 39-240) and 54 (range 36-340) U.l-1, respectively], and then decreased after 64 and 88 h at altitude [34 (range 18-290) and 31 (range 17-104) U.l-1, respectively]. These changes of serum-EPO concentration were correlated to the changes in arterial blood oxygen saturation (r = -0.60, P = 0.0009), pH (r = 0.67, P = 0.003), and in-vivo venous blood oxygen half saturation tension (r = -0.68, P = 0.004) but not to the changes in 2, 3 diphosphoglycerate. After 64 h at altitude, six of the nine subjects had down-regulated their serum-EPO concentrations so that median values were three times above those at sea level. These six subjects had significant diurnal variations of serum-EPO concentration at sea level; the nadir occurred between 0800-1600 hours [6 (range 4-13) U.l-1], and peak concentrations occurred at 0400 hours [9 (range 8-14) U.l-1, P = 0.02]. After 64 h at altitude, the subjects had significant diurnal variations of serum-EPO concentration; the nadir occurred at 1600 hours [20 (range 16-26) U.l-1], and peak concentrations occurred at 0400 hours [31 (range 20-38) U.l-1, P = 0.02]. This study demonstrated diurnal variations of serum-EPO concentration in normoxia and hypoxia, with comparable time courses of median values. The results also suggested that EPO production at altitude is influenced by changes in pH and haemoglobin oxygen affinity.

Application of a modified INCSTAR Epo-trac 125/RIA for measurement of serum erythropoietin concentration in elite athletes

OBJECTIVES

To evaluate the analytical performance of a radioimmunoassay for measurement of erythropoietin.

DESIGN AND METHODS

The INCSTAR Epo-trac 125I radioimmunoassay was examined for applications requiring sensitivity and precision within the normal range.

RESULTS

Sensitivity was improved by increasing sample volume to 300 microL. Minimal detectable concentration was determined at 5.3 U/L, %CV ranged from 4.8-5.8 and 13.3-6.4 for intra- and inter-assay imprecision, respectively. Accuracy was maximized by controlling for lipemic and hemolyzed samples and ensuring serum was separated from the clot within 1 h of collection. Values demonstrated good correlation to the Diagnostic Systems Laboratory RIA-kit.

CONCLUSIONS

With sample volume increased to 300 microL and control of sample preparation, the INCSTAR Epo-trac 125/RIA showed improved precision. Assay sensitivity at lower values allows resolution of changes in erythropoietin within the normal reference range. Age was not found to influence erythropoietin concentration. Within 10 days sojourn at moderate altitude an increase in circulating erythropoietin and reticulocytosis was observed in swimmers.

An early effect of acute plasma volume expansion in humans on serum erythropoietin concentration

The effect of acute plasma volume change in humans on serum erythropoietin [EPO]s, plasma active renin [REN] and plasma aldosterone [ALDO] concentrations was examined. Plasma volume (PV) expansion was induced by intravenous infusion of 150 ml (30g) of plasma albumin and 500 ml of physiological saline. The [EPO]s decreased by 14.3% (corrected values for PV expansion) and remained decreased for 5 h. The [REN] was decreased by more than 25% during the day of the experiment and [ALDO] by more than 60%. Only a weak positive correlation was found between [EPO]s and [REN] (r = 0.35; P < 0.05) but a lack of correlation between changes in PV and [EPO]s as well as between [EPO]s and [ALDO] was seen. We postulated that in healthy men an acute PV expansion by 10% to 17.5% would not appear to promote stimulation of EPO synthesis for at least 11 h. Since a weak positive correlation was observed between [EPO]s and [REN] and a lack of correlation between [EPO]s and [ALDO], it would seem that there is no direct link between [REN] and [ALDO] and erythropoietin synthesis in healthy subjects.

Hematocrit levels in sleep apnea

This study addresses the hypothesis that patients with obstructive sleep apnea, who exhibit recurrent episodes of oxygen desaturation at night, have higher hematocrit levels than nonapneic control subjects. We prospectively studied 624 patients referred to the sleep disorders center at St. Michael's Hospital because of suspicion of sleep apnea. All patients had nocturnal polysomnography and measurements of hematocrit level, hemoglobin value, WBC count, and platelet count. Smoking history and awake oxygen saturation (SaO2) was recorded in all of them. Nocturnal oxygenation was assessed using three indices: lowest nocturnal SaO2 (LoSaO2), mean nocturnal SaO2 (MnSaO2) and percent of total sleep time spent at SaO2 lower than 85 percent (TST85%). Patients with TST85% in the lowest quartile (TST85% = 0) had minimally lower hematocrit levels than patients with TST85% in the highest quartile (8 < or = TST85% < or = 90): 0.41 +/- 0.03 vs 0.40 +/- 0.02 in female subjects and 0.45 +/- 0.05 vs 0.43 +/- 0.05 in male subjects, respectively (p < 0.05). Multiple linear regression analysis revealed that MnSaO2, age, and pack-years of smoking were significant predictors of hematocrit level, but they accounted for only 9 percent of the variability in hematocrit level (multiple R2 = 0.087; p < 0.05). We conclude that intermittent nocturnal hypoxemia during episodes of apnea does not lead to clinical polycythemia, but is associated with minor elevations in hematocrit value. These small elevations are unlikely to be useful as markers of hypoxic stress associated with sleep apnea.

Diurnal variations of serum erythropoietin in trained and untrained subjects

The diurnal variations of serum-erythropoietin concentration ([s-EPO]) were investigated in six physically trained (T) and eight untrained (UT) men. The T subjects had a higher mean maximal oxygen uptake than UT subjects [75.7 (SEM 1.6) ml.min-1.kg-1 versus 48.3 (SEM 1.4) ml.min-1.kg-1, P < 0.0001] and a lower mean body mass index [BMI, 21.7 (SEM 0.7) kg.m-2 versus 24.4 (SEM 0.6) kg.m-2, P = 0.02]. Each subject was followed individually for 24 h as they performed their normal daily activities. Venous blood samples were collected from awakening (0 min) until the end of the 24-h period (1440 min). Both T and UT had a nadir of [s-EPO] 120 min after awakening [10.0 (SEM 0.3) U.l-1 versus 11.5 (SEM 2.1) U.l-1, P > 0.05]. The UT and T increased their [s-EPO] to peak values at 960 min and 960-1200 min, respectively (ANOVA P = 0.03) after awakening [UT: 18.4 (SEM 2.8) U.l-1; T: 16.2 (SEM 2.5) U.l-1, P > 0.05]. The mean 24-h [s-EPO] were 14.5 (SEM 1.0) U.l-1 and 14.9 (SEM 0.9) U.l-1 in T and UT, respectively (P > 0.05). The individual mean 24-h [s-EPO] were not correlated to body mass, BMI or maximal oxygen uptaken. Significant diurnal variations in [s-EPO] occurred in these healthy subjects irrespective of their levels of physical activity.

Clinical validation of an RIA for natural and recombinant erythropoietin in serum and plasma

A sensitive radioimmunoassay (RIA) for the detection of erythropoietin (EPO) was developed using antibody directed against EPO from human urine. With 100 microL of sample, the assay is sensitive to 7 U/L, well below the mean EPO level in normal males (15.1 +/- 3.5 U/L) or females (15.4 +/- 4.8 U/L). Dilutions of a variety of human serum samples show a parallel relationship with the standard EPO. Clinical validation of the RIA was confirmed by appropriate increases or decreases of EPO levels in various types of anemia and polycythemia. Serum EPO levels were also measured in volunteers participating in an autologous blood donation study. The RIA proved to be quite sensitive, detecting small increases even after a single unit phlebotomy. This RIA of human EPO meets all the requirements of a routine clinical assay in terms of specificity and clinical sensitivity and can be easily conducted in routine clinical laboratories.

The effect of short and long duration exercise on serum erythropoietin concentrations

The effects of short and long duration exercise on serum erythropoietin concentrations [EPO]s were studied in seven male cross-country skiers of national team standard and eight male marathon runners, respectively. The short duration exercise was performed as 60 min of cycling at an intensity of 80%-95% of maximal heart rate. Arterial blood oxygen saturations monitored by pulse-oximetry remained unchanged throughout exercise. The partial pressure of O2 at which haemoglobin was half-saturated with O2 calculated from forearm venous blood gas tension and blood O2 saturation, and the erythrocyte 2,3-diphosphoglycerate did not change significantly during the exercise. Blood lactate concentrations were increased at the end of exercise [from 1.3 (SEM 0.1) to 3.6 (SEM 0.3) mmol.l-1]. The [EPO]s determined (by enzyme-linked immunosorbent assay) pre-exercise, 5 min, 6 h, 19 h, and 30 h after the exercise were unchanged [from 16.1 (SEM 2.6) to 19.1 (SEM 3.2), 17.9 (SEM 3.0), 17.0 (SEM 2.5), and 18.6 (SEM 2.9) U.l-1, respectively]. The [EPO]s were not correlated to the earlier parameters. The long duration exercise consisted of habitual training, a 3 week break from training followed by 2 and 4 weeks of re-training. The [EPO]s, body fat (BF), and serum free-testosterone concentrations determined at the end of each period remained unchanged. The maximal oxygen uptakes were decreased after the break from training and increased during retraining (P = 0.04). Body mass (mb) increased after the break in training (P = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)