Fenoterol but not dobutamine increases erythropoietin production in humans

The effects of normoxic endurance exercise on erythropoietin (EPO) production and the impact of selective β1 and non-selective β1 + β2 adrenergic receptor blockade

PURPOSE

Habitual endurance exercise results in increased erythropoiesis, which is primarily controlled by erythropoietin (EPO), yet studies demonstrating upregulation of EPO via a single bout of endurance exercise have been equivocal. This study compares the acute EPO response to 30 min of high versus 90 min of moderate-intensity endurance exercise and whether that response can be upregulated via selective adrenergic receptor blockade.

METHODS

Using a counterbalanced, cross-over design, fifteen participants (age 28 ± 8) completed two bouts of running (30-min, high intensity vs 90-min, moderate intensity) matched for overall training stress. A separate cohort of fourteen participants (age 31 ± 6) completed three bouts of 30-min high-intensity cycling after ingesting the preferential β₁-adrenergic receptor (AR) antagonist bisoprolol, the non-preferential β₁ + β₂ antagonist nadolol or placebo. Venous blood was collected before, during, and after exercise, and serum EPO levels were determined by ELISA.

RESULTS

No detectable EPO response was observed during or after high intensity running, however, in the moderate-intensity trial EPO was significantly elevated at both during-exercise timepoints (+ 6.8% ± 2.3% at 15 min and + 8.7% ± 2.2% at 60 min). No significant change in EPO was observed post-cycling or between the trials involving βAR blockade.

CONCLUSION

Neither training mode (running or cycling), nor beta-blockade significantly influenced the EPO response to 30 min of high-intensity exercise, however, 90 min of moderate-intensity running elevated EPO during exercise, returning to baseline immediately post-exercise. Identifying the optimal mode, duration and intensity required to evoke an EPO response to exercise may help tailor exercise prescriptions designed to maximize EPO response for both performance and clinical applications.

Central venous oxygenation: when physiology explains apparent discrepancies

Central venous oxygen saturation (ScvO₂) >70% or mixed venous oxygen saturation (SvO₂) >65% is recommended for both septic and non-septic patients. Although it is the task of experts to suggest clear and simple guidelines, there is a risk of reducing critical care to these simple recommendations. This article reviews the basic physiological and pathological features as well as the metrological issues that provide clear evidence that SvO₂ and ScvO₂ are adaptative variables with large inter-patient variability. This variability is exemplified in a modeled population of 1,000 standard ICU patients and in a real population of 100 patients including 15,860 measurements. In these populations, it can be seen how optimizing one to three of the four S(c)vO₂ components homogenized the patients and yields a clear dependency with the fourth one. This explains the discordant results observed in large studies where cardiac output was increased up to predetermined S(c)vO₂ thresholds following arterial oxygen hemoglobin saturation, total body oxygen consumption needs and hemoglobin optimization. Although a systematic S(c)vO₂ goal-oriented protocol can be statistically profitable before ICU admission, appropriate intensive care mandates determination of the best compromise between S(c)vO₂ and its four components, taking into account the specific constraints of each individual patient.

Role of Renal Nerves and Salt Intake on Erythropoietin Secretion in Rats following Carbon Monoxide Exposure

Because the data from the literature contain conflicting results regarding the role of renal nerves and angiotensin II in hypoxia-induced erythropoietin (EPO) secretion, we evaluated the effect of renal nerves and salt intake in rats on EPO secretion stimulated by carbon monoxide (CO). Serum levels and renal mRNA content of EPO were similarly elevated by exposure to different CO concentrations in a dose-dependent manner in rats with bilateral renal denervation (DNX) and in sham-denervated controls (INN). However, at 600 ppm CO, serum concentrations and mRNA of EPO were significantly higher in DNX compared with INN rats (p < 0.05). This increase of EPO secretion in DNX rats could be blocked by administration of neuropeptide Y (NPY) (p < 0.05), whereas the NPY receptor antagonist did not enhance EPO secretion in INN rats after CO exposure. Agonists and antagonists of beta-adrenergic receptors had no effect on EPO secretion. High-salt (HS) diet reduced EPO secretory response at 600 ppm CO by 55% compared with INN rats on normal salt diet (p < 0.01). In addition, DNX increased EPO secretion in rats on low-salt and HS diet, whereas plasma renin activity did not correlate with EPO levels under these experimental conditions. In summary, our data suggest that renal nerves contribute to the half-maximal EPO secretory response to CO exposure, possibly via NPY receptors.

Erythropoietin production: Molecular mechanisms of the antagonistic actions of cyclic adenosine monophosphate and interleukin-1

Erythropoietin (Epo) mRNA expression is suppressed by interleukin 1 (IL-1). Cyclic adenosine monophosphate (cAMP) can increase Epo mRNA and Epo protein levels in IL-1 treated HepG2 cells to some extent. To identify molecular mechanisms of this reaction we investigated three transcription factors (NF-kappaB, GATA-2 and HIF-1) that control the Epo gene. Western blot analyses and electrophoretic mobility shift assays (EMSAs) revealed that IL-1 strongly activated NF-kappaB, which is a likely suppressor of the Epo promoter. Treatment of the cells with dibutyryl-cAMP (Bt2-cAMP) inhibited the activation of NF-kappaB by IL-1. Bt2-cAMP increased GATA-2 DNA binding. Since GATA-2 is a suppressor of the Epo promoter, GATA-2 activation was unlikely to cause the increase of Epo mRNA expression in IL-1 treated cells. Furthermore, Western blots, EMSAs and reporter gene studies showed that Bt2-cAMP was without effect on the hypoxia-inducible transcription factor HIF-1. Thus, NF-kappaB is probably the primary transcription factor by which cAMP counteracts the inhibition of Epo gene expression by IL-1.

Do alterations of endogenous angiotensin II levels regulate erythropoietin production in humans?

AIMS

Recent evidence suggests a potential role of angiotensin II in the physiological regulation of erythropoietin (Epo) production. While the administration of exogenous angiotensin II (AII) has been used so far to study its effects, the role of endogenous AII has remained unclear.

METHODS

To alter endogenous AII in humans experimentally we used furosemide bolus injection as a short-term (study 1) and dietary salt as a long-term modulator (study 2). In an open crossover design, 12 healthy male volunteers received furosemide (F) 0.5 mg kg(-1) intravenously or placebo (P) in random order (study 1). With the same design, 12 volunteers received high-salt (HS), normal-salt (NS) and low-salt (LS) diet (study 2). Plasma renin activity (PRA) was analysed along with AII. Inulin and paraaminohippurate (PAH) clearances were used to indicate glomerular filtration rate (GFR) and renal plasma flow (RPF), respectively.

RESULTS

While F stimulated AII and PRA and decreased GFR and RPF significantly, no concomitant alteration of Epo was observed [AUCEpo: placebo 5709 +/- 243 (% of baseline x h), furosemide: 5833 +/- 255 (% of baseline x h); 95% confidence interval (CI) -608.4, 856.0; P = 0.73]. F decreased GFR (from 103.6 +/- 4.0 to 90.6 +/- 4.8 ml min(-1) 1(-1) 73 m-2; 95% CI 1.1, 24.9; P < 0.05), but not RPF (study 1). Correspondingly, LS stimulated and HS decreased AII and PRA significantly. HS increased GFR and RPF. Again, Epo concentrations were not affected (AUCEpo: normal sodium 44 +/- 6.7 mIU x day ml(-1), low sodium 39 +/- 2.4 mIU x day ml(-1), high sodium 48.5 +/- 6.1 mIU x day ml(-1); normal salt/low salt 95% CI -11.9, 21.9, P = 0.54; normal salt/high salt 95% CI -14.4, 23.3, P = 0.63; study 2).

CONCLUSIONS

We conclude that, at least in the physiological setting in healthy volunteers, increased concentrations of endogenous AII may not be a major factor of Epo regulation.

Determination of fenoterol in human plasma by HPLC with fluorescence detection after derivatization

A new method for the determination of fenoterol is described, which uses HPLC separation with fluorescence detection. Dobutamine is employed as an internal standard. The separation was achieved on a short reversed phase column with a mobile phase consisting of water, acetonitrile and methanol. Prior to chromatography both analytes are derivatized with 9-chloroformyl-carbazole. Isolation of the analytes from plasma is carried out by liquid-liquid extraction into 2-butanol after protein precipitation with acetonitrile. The method is capable of estimating fenoterol concentrations in the sub-nanogram per ml range with sufficient accuracy and precision. The determination of fenoterol can now be carried out in the average laboratory without radiolabelled material.

Influence of controlled hypoxia and radical scavenging agents on erythropoietin and malondialdehyde concentrations in humans

The present study was carried out to evaluate a model of a hypoxic stimulus of erythropoietin (EPO) production in humans and to investigate the role of free oxygen radicals in human EPO production. The study was conducted as an open, randomized, parallel, placebo-controlled trial. Thirty-six healthy male volunteers received a hypoxic treatment (13% O(2)) with a respiration mask for 6 h. During the period of hypoxia, the volunteers received as a short-term treatment either 1200 mg thioctic acid, or N-acetylcysteine 600 mg or placebo (0.9% sodium chloride). The EPO concentration in plasma increased up to 290% of the baseline level in all three groups. No statistically significant differences of AUC(EPO(0-48 h)) could be demonstrated between the groups. The malondialdehyde (MDA) concentration in plasma increased significantly (P < 0.001) 2 h after termination of hypoxia (mean 129.8 +/- 6.8% of the baseline) in all three groups.

CONCLUSIONS

Taken together, our in-vivo results do not support a gross modulatory effect of a short-term treatment with radical scavenging agents on EPO-production during or after hypoxia in humans, as derived from the detected changes of MDA-concentrations in peripheral plasma.

Angiotensin II increases erythropoietin production in healthy human volunteers

BACKGROUND

A number of animal studies and our own clinical trials point towards a possible influence of the renin-angiotensin-system (RAS) on erythropoietin (EPO) production. In this study we investigated the role of angiotensin II in the regulation of EPO production in humans.

METHODS

After a hemorrhage of 750 ml as a basic physiological stimulus 72 healthy male volunteers received in a parallel design either placebo (physiologic electrolyte solution) for 6 h, angiotensin II i.v. for 6 h (1-3 microgram min-1, sufficient to increase systolic blood pressure by 20 mmHg), the selective AT1-receptor antagonist losartan, the ACE-inhibitor captopril, angiotensin II + losartan, or angiotensin II + captopril.

RESULTS

Administration of angiotensin II alone and in combination with captopril resulted in a significantly higher Cmax EPO (67% higher vs. placebo, P < 0.05) and AUCEPO (0-24h) (40% higher vs. placebo, P < 0.05). In the groups receiving losartan or captopril alone or the combination of angiotensin II + losartan no significant difference of Cmax EPO and AUCEPO(0-24h) compared to placebo could be detected.

CONCLUSIONS

This study shows in a model of controlled, basic physiological stimulation of renal EPO production that angiotensin II is able to increase EPO levels in humans. This effect of angiotensin II can be blocked by the specific AT1-receptor antagonist losartan but not by the ACE-inhibitor captopril. The result may be interpreted as a hint that one signal for the control of EPO production in humans may be mediated by angiotensin II (AT1)-receptors.

Fenoterol stimulates human erythropoietin production via activation of the renin angiotensin system

AIMS

The present study assessed the hypothesis that the beta2 sympathomimetic fenoterol influences the production of erythropoietin (EPO) by activation of the renin angiotensin system (RAS), i.e. angiotensin II.

METHODS

In an open, parallel, randomized study healthy volunteers received i.v. either placebo (electrolyte solution), fenoterol or fenoterol in combination with an oral dose of the AT1-receptor antagonist losartan.

RESULTS

Compared with placebo treatment AUCEPO(0,24 h) was significantly increased after fenoterol application by 48% whereas no increase in the group receiving fenoterol and losartan could be detected. The rise of PRA was statistically significant under fenoterol and fenoterol plus lorsartan.

CONCLUSIONS

Stimulation of EPO production during fenoterol infusion appears to be angiotensin II-mediated. Thus, angiotensin II may be considered as one important physiological modulator of EPO production in humans.

Fenoterol increases erythropoietin concentrations during tocolysis

AIMS

The present study was carried out to assess the effect of the selective beta2-adrenoceptor agonists on erythropoietin (EPO) production.

METHODS

Routine tocolysis with fenoterol (using the regular rate of 2 microg min[-1]) was used as a clinically easily accessible model.

RESULTS

EPO concentrations had doubled 24 h after the start of tocolysis (P < 0.001). This increase lasted over the entire observation period of 48 h. Potassium concentrations fell significantly during the first hours of fenoterol infusion. There was no increase of human placenta lactogen during the period of EPO increase.

CONCLUSIONS

The data confirm our earlier results that fenoterol increases EPO concentrations following haemorrhage. In this model it was not necessary to stimulate EPO production prior to pharmacological treatment.