Adaptative mechanism of the equilibrative nucleoside transporter 1 (ENT-1) and blood adenosine levels in elite freedivers.

PURPOSE: Long static or intense dynamic apnoea-like high-altitude exposure is inducing hypoxia. Adenosine is known to participate to the adaptive response to hypoxia leading to the control of heart rate, blood pressure and vasodilation. Extracellular adenosine level is controlled through the equilibrative nucleoside transporter 1 (ENT-1) and the enzyme adenosine deaminase (ADA). The aim of this study was to determine the control of adenosine blood level (ABL) via ENT-1 and ADA during apnoea-induced hypoxia in elite freedivers was similar to high-altitude adaptation. METHODS: Ten freediver champions and ten controls were studied. Biological (e.g. ENT-1, ADA, ABL, PaO2, PaCO2 and pH) and cardiovascular (e.g. heart rate, arterial pressure) parameters were measured at rest and after a submaximal dry static apnoea. RESULTS: In freedivers, ABL was higher than in control participants in basal condition and increased more in response to apnoea. Also, freedivers showed an ADA increased in response to apnoea. Finally, ENT-1 level and function were reduced for the free divers. CONCLUSION: Our results suggest in freedivers the presence of an adaptive mechanism similar to the one observed in human exposed to chronic hypoxia induced by high-altitude environment.

Adenosine plasma level correlates with homocysteine and uric acid concentrations in patients with coronary artery disease.

The role of hyperhomocysteinemia in coronary artery disease (CAD) patients remains unclear. The present study evaluated the relationship between homocysteine (HCys), adenosine plasma concentration (APC), plasma uric acid, and CAD severity evaluated using the SYNTAX score. We also evaluated in vitro the influence of adenosine on HCys production by hepatoma cultured cells (HuH7). Seventy-eight patients (mean age ± SD: 66.3 ± 11.3; mean SYNTAX score: 19.9 ± 12.3) and 30 healthy subjects (mean age: 61 ± 13) were included. We incubated HuH7 cells with increasing concentrations of adenosine and addressed the effect on HCys level in cell culture supernatant. Patients vs. controls had higher APC (0.82 ± 0.5 µmol/L vs 0.53 ± 0.14 µmol/L; p < 0.01), HCys (15 ± 7.6 µmol/L vs 6.8 ± 3 µmol/L, p < 0.0001), and uric acid (242.6 ± 97 vs 202 ± 59, p < 0.05) levels. APC was correlated with HCys and uric acid concentrations in patients (Pearson's R = 0.65 and 0.52; p < 0.0001, respectively). The SYNTAX score was correlated with HCys concentration. Adenosine induced a time- and dose-dependent increase in HCys in cell culture. Our data suggest that high APC is associated with HCys and uric acid concentrations in CAD patients. Whether the increased APC participates in atherosclerosis or, conversely, is part of a protective regulation process needs further investigations.

Early ventilation-heart rate breakpoint during incremental cycling exercise.

Previous observations having reported a transient hypoxia at the onset of incremental exercise, we investigated the existence of concomitant ventilatory and heart rate (HR) breakpoints.33 subjects executed a maximal cycling exercise with averaging for successive 5-s periods of HR, ventilation, tidal volume (VT), mean inspiratory flow rate (VT/Ti), and end-tidal partial pressures of O2 (PETO2) and CO2. In 10 subjects, the transcutaneous partial pressure of O2 (PtcO2) was recorded and the venous blood lactic acid (LA) concentration measured.At the beginning of exercise, PETO2 decreased, reaching a nadir, then progressively increased until the exercise ended. PtcO2 varied in parallel. Whether or not a 0-W cycling period preceded the incremental exercise, the rate of changes in VE, VT, VT/Ti and HR significantly increased when the nadir PO2 was reached. The ventilatory/ HR breakpoint was measured at 33±4% of VO2max, whereas the ventilatory threshold (VTh) was detected at 67±4% of VO2max and LA began to increase at 45 to 50% of VO2max.During incremental cycling exercise, we identified the existence of HR and ventilatory breakpoints in advance of both lactate and ventilatory thresholds which coincided with modest hypoxia and hypercapnia.

A2A adenosine receptor function in patients with vasovagal syncope.

AIMS: Adenosine is a possible mediator in vasovagal syncope (VVS) via the activation of its receptors. High expression of adenosine A2A receptors (A2AR) has been reported in VVS. The function of these over-expressed receptors in this population has never been evaluated. METHODS AND RESULTS: We used Adonis, a specific-made antibody with A2AR agonist properties, to evaluate binding parameters (i.e. dissociation constant KD) and cAMP production (i.e. EC50) by peripheral blood mononuclear cells of 16 VVS patients. Eight healthy volunteers served as controls. A2AR expression was higher in patients than controls; mean: 11.5 ± 1.2 vs. 7.7 ± 0.8 AU, P = 0.04. Also, KD values were higher in patients than controls: 2.1 ± 0.02 × 10(-7) vs. 5 ± 1 × 10(-8) M, P < 0.01 In controls, KD values were lower than EC50 (5 ± 1.7 × 10(-8) vs. 2.8 ± 0.4 10(-7) M, P < 0.01), but in patients, KD values did not differ from EC50: 2. ± 0.2 × 10(-7) vs. 2.5 ± 0.4 × 10(-7) M, P > 0.05. However, four patients had lower EC50 (3.5 ± 0.3 × 10(-8) M) than KD (2.9 ± 1.2 × 10(-7) M; KD/EC50 = 9.6), suggesting the presence of spare receptors. CONCLUSION: The function of A2AR of patients with VVS was preserved since their stimulation by Adonis led to cAMP production with an EC50 comparable with those in controls. However, their affinity was lower than those of controls. Our results suggest that A2AR are implicated in the physiopathology of VVS.

Rapid differential diagnosis of diabetes insipidus in a 7-month-old infant: The copeptin approach.

INTRODUCTION: Diabetes insipidus is characterized by hypoosmotic polyuria related to deficiency of arginine-vasopressin (AVP) secretion (central diabetes insipidus, CDI) or renal insensitivity to AVP (nephrogenic diabetes insipidus, NDI). The water deprivation test with assessment of AVP activity is currently the gold standard for differential diagnosis in patients presenting polyuria-polydipsia syndrome. Nevertheless, it can be dangerous without proper surveillance and its interpretation may be challenging. Other markers have been suggested. Direct quantification of circulating AVP is not sufficient for diagnosis: vasopressin is unstable, analysis is complex. AVP comes from prohormone preprovasopressin with concomitant release of copeptin (C-terminal moiety) in the equimolar ratio. Copeptin is stable in vitro, with easy and rapid measurement (<4h). Past studies have shown greater sensitivity and specificity of copeptin versus AVP to discriminate etiologies of polyuria in adults, but its value has not been demonstrated in infants yet. OBSERVATION: A 7-month-old infant presented polyuria-polydipsia syndrome with poor weight gain. Laboratory tests pointed out hypernatremia (170mmol/L) and blood hyperosmolarity (330mOsm/L) with inappropriate urinary hypoosmolarity (168mOsm/L). Plasmatic copeptin measurement was found at a very high level, 303pmol/L (1-14pmol/L). DdAVP administration did not improve the polyuria, confirming the final diagnosis of NDI. Hyperhydration with a hypoosmolar diet normalized the hydration status and circulating levels of copeptin within 1 week. CONCLUSION: Copeptin, a stable peptide reflecting AVP secretion, could be a safer and faster biomarker for etiological diagnosis of polyuria-polydipsia syndrome in children. Before regularization of hydration status, a single baseline measurement may be enough to discriminate NDI from other etiologies without the water deprivation test.

Adenosine plasma concentration in pulmonary hypertension.

OBJECTIVE: In this study, we sought to appreciate the role of adenosine in the regulation of pulmonary vascular tone, especially in the case of clinical pulmonary hypertension, by investigating the relationship between endogenous plasma adenosine levels and pulmonary artery vasoconstriction. METHODS: Adenosine plasma concentrations, were measured simultaneously in the distal right pulmonary artery and in the femoral artery, both at steady state (room air) and during pure oxygen inhalation. Three clinical situations were considered: (1) normal hemodynamics [7 control subjects, mean pulmonary artery pressure (MPAP) = 18.5 +/- 1 mm Hg], (2) moderate pulmonary hypertension secondary to chronic obstructive pulmonary disease (COPD), (8 patients, MPAP = 31 +/- 3 mm Hg), (3) severe primary pulmonary hypertension (PPH), (8 patients, MPAP = 70 +/- 5 mm Hg). RESULTS: In every instance, adenosine evaluated by HPLC was higher in the pulmonary than in the systemic circulation. For room air, adenosine plasma concentrations were significantly lower in COPD (0.49 +/- 0.16 mumol l-1) and PPH patients (0.45 +/- 0.14 mumol l-1) than in controls (1.26 +/- 0.12 mumol l-1). During O2 administration, adenosine plasma concentrations all decreased but more so in COPD and PPH patients. The significant correlations between adenosine plasma concentrations and both pulmonary vascular resistance and PvO2, in controls, were not found in COPD or PPH patients. CONCLUSION: The adenosine plasma concentrations in the pulmonary circulation of PPH and COPD patients are low, and may contribute to pulmonary artery hypertension.

Pain relief achieved by transcutaneous electrical nerve stimulation and/or vibratory stimulation in a case of painful legs and moving toes.

A patient is described with painful legs and moving toes. The pain had been occurring for more than 15 years, and a variety of therapies had been attempted with only partial, if any, success. Only morphine had succeeded in relieving the pain, but it had to be discontinued to avoid tolerance and dependence. We devised a treatment consisting of transcutaneous electrical nerve stimulation (TENS), vibratory stimulation (VS), and a combination of the two methods (TENS + VS). TENS brought about partial pain relief, but was less effective than VS; dual stimulation (TENS + VS) led to complete alleviation of the pain. Four months later, the patient was applying dual stimulation himself at home and was thus able to maintain complete relief with 3 or 4 weekly sessions. We suggest that dual stimulation results in a large-scale recruitment of large-diameter afferent fibres and may thus set up a powerful inhibitory control of nociception in our patient.

Adenosine and neuropathic pain.

Recent studies have reported the possibilities of relieving neuropathic pain by administering adenosine or its analogs. In order to determine if there exists a metabolic anomaly of this nucleoside in patients with neuropathic pain, circulating adenosine levels were compared in three patient groups. The first was composed of individuals suffering from neuropathic pain, the second of patients with nervous system lesions in the absence of pain, and the third was composed of patients suffering from pain resulting from excessive nociception. The adenosine blood levels of these patients were compared to those of a control group. Finally, adenosine in the cerebrospinal fluid (CSF) of some patients was also assayed. The results show that there are reduced levels of blood and CSF adenosine in patients with neuropathic pain. This adenosine deficiency could explain the potential therapeutic effects of administering adenosine or its analogs.

Plasma beta-endorphin and adenosine concentration in pulmonary hypertension.

To determine whether beta-endorphin plays a role in the regulation of pulmonary vascular tone in patients with pulmonary hypertension, we investigated the relations between hemodynamics and beta-endorphin and adenosine concentrations in 3 clinical situations: (1) normal hemodynamics (7 subjects, mean pulmonary artery [PA] pressure 18.5 +/- 1 mm Hg); (2) moderate pulmonary hypertension secondary to chronic obstructive pulmonary disease (COPD) (8 patients, mean PA pressure 31 +/- 3 mm Hg); and (3) severe primary pulmonary hypertension (PPH) (8 patients, mean PA pressure 70 +/-5 mm Hg). Plasma beta-endorphin and adenosine were measured in a distal PA and in the femoral artery in room air and during oxygen inhalation. Beta-endorphin levels were similar in the pulmonary and systemic circulations. No difference was observed between patients with COPD and PPH, but relative to controls, both had significantly higher beta-endorphin levels. Pulmonary adenosine was significantly lower in patients with pulmonary hypertension than in controls (-60% in COPD [p <0.005] and -70% in PPH [p <0.001]). Pure oxygen administration significantly decreased adenosine and beta-endorphin levels, much more so in patients with COPD and PPH. We found a negative correlation between beta-endorphin and adenosine concentrations (r = -0.751, p <0.001): the higher the adenosine, the lower the beta-endorphin level. These observations suggest that because adenosine release by pulmonary vascular endothelium is reduced in pulmonary hypertension, the resulting worsened hypoperfusion and tissue oxygenation may cause increased beta-endorphin release.

Relationships between the anti-HIV V(3)-derived peptide SPC(3) and lymphocyte membrane properties involved in virus entry: SPC(3) interferes with CXCR(4).

SPC(3) is a multiple antigen peptide derived from the V(3) loop of human immunodeficiency virus (HIV) envelope (Env). It exerts a potent anti-HIV activity whereas it alters neither Env expression nor binding to CD(4). Here, SPC(3) binding characteristics, its subsequent intracellular fate and the fact that it inhibited SDF(1)alpha binding to the lymphocyte surface provided strong arguments to conclude that it exerts its anti-HIV activity through interference with the CXCR(4) coreceptor. In contrast, it interferes with none of the other major surface proteins and mechanisms involving V(3) and implicated in infection, as shown here. This work identifies the target mechanism of SPC(3).

Modulation of adenosine concentration by opioid receptor agonists in rat striatum.

There is evidence that adenosine and morphine interact in the striatum. However, little is known about the precise role of the opioid receptor subtypes implicated in the modulation of adenosine tissue concentration and in adenosine receptor expression and function. We sought to evaluate, in the absence of withdrawal symptoms, the effects of the short-term administration of selective mu-, delta- or kappa-opioid receptor agonists on adenosine concentration and on adenosine A(2A) receptor function in rat striatum. Adenosine A(2A) receptor was chosen because the neuronal sub-population expressing this receptor coexpresses enkephalin, suggesting that adenosine A(2A) receptor may be regulated by opioid receptor agonists. Oxymorphone hydrochloride mu-opioid receptor agonist, 6 mg/kg/day), +[-(5 alpha,7 alpha, 8 beta)-(-)-N-methyl-N(7-(1-pyrrolidinyl)1-oxaspiro (4.5)dec-8-yl) benzenacetamide] (U69593) (kappa-opioid receptor agonist, 0.75 mg/kg/day), and (+)-4[(alpha R)-alpha-((2S,5R)-4-allyl-2, 5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide) (SNC80) (delta-opioid receptor agonist, 9 mm/kg/day), or vehicle, were administered i.p 3 x daily during 5 days to groups of rats (n=6). We also investigated the effects of opioid receptor agonists on adenosine uptake by striatal cell extracts. We found that administration of mu- or delta-opioid receptor agonists significantly decreased adenosine uptake in striatal cell extracts and increased adenosine concentration (mean+24% and +45% for mu- and delta-opioid receptor agonist, respectively, relative to controls). None of the receptor agonists tested induced obvious modifications of adenosine A(2A) receptor function. However, the delta-opioid receptor agonist induced an increase in adenosine A(2A) mRNA expression (mean 44%). We conclude that mu and delta receptor agonists inhibit adenosine uptake by striatal cell extracts and increase adenosine concentrations in rat striatum.

Use of HPLC to measure circulating adenosine levels in migrainous patients.

Adenosine is a powerful natural vasodilator that could be involved in migraine. It is difficult to assay this nucleoside, however, because it has a short half-life. We have used HPLC to compare the concentrations of blood adenosine sampled in crisis-free intervals and during crisis periods in ten patients with common migraine and have compared these levels to those noted in a control population. Our sampling technique uses vacuum suction and enables rapid mixing of the blocking solution and whole venous blood. This results in reproducible HPLC assays. We also show that, during a migraine crisis, mean blood adenosine levels increase by 47%. However, the origin of this adenosine release is difficult to define.

The use of HPLC to evaluate the variations of blood coronary adenosine levels during percutaneous transluminal angioplasty.

Although it is well established that adenosine is released during acute ischemia, little is known of the behaviour of adenosine levels following treatment of coronary lesion by percutaneous transluminal coronary angioplasty (PTCA). Using high performance liquid chromatography, we measured intracoronary adenosine levels before and 5 min after PTCA in ten patients with one-vessel disease and a significant (> 70%) coronary stenosis. Adenosine levels decrease in all patients after PTCA. Nevertheless, more studies are now necessary to evaluate the possible predictive value (with regard to restenosis) of coronary adenosine levels after PTCA.

In vivo neurotoxicity of Androctonus australis hector scorpion venom: evidence that the supra-thoracic nervous system is not implicated in the clinical manifestations.

The severity of scorpion stings is related to the highly active neurotoxins in the venom. In this study, rats whose supra-spinal central nervous system was deprived of its peripheral connections were experimentally poisoned by the venom of Androctonus australis hector scorpion. Clinical signs of severity were not modified when the rats had previously undergone high medullar section. These results suggest that the supra-thoracic nervous system is not implicated in the neurotoxicity manifestations of scorpion envenomation.

Nociceptive threshold in patients with epilepsy.

Clinical practitioners have often observed in the course of their daily work that the pain thresholds of epileptic patients seem to differ from those of healthy subjects. These patients can suffer from quite severe traumatic lesions without apparently experiencing any pain. Since they are usually under treatment for epilepsy, it is difficult to determine whether the absence of pain is due to these patients' epileptic condition or to its treatment, since most antiepileptic drugs also have analgesic effects. In the present study, it was proposed to assess the pain thresholds of 15 epileptic patients (10 with tonic-clonic seizures generalized at outset and 5 with temporal lobe epilepsy), by measuring the leg flexion nociceptive reflex (or RIII reflex) threshold: the stimulation threshold at which this reflex is triggered is known to be correlated with the pain threshold. The nociceptive threshold of the patients with generalized epilepsy was not found to differ from that of the control population, whereas that of the patients with temporal lobe epilepsy was spontaneously high and was not reversed upon injecting naloxone. These data are discussed from the point of view of the pain pathways and mechanisms possibly involved.

An ultrarapid prognostic index in microprolactinoma surgery.

OBJECT: Prolactinomas account for approximately 40% of pituitary tumors. If the tumor does not exceed 10 mm at its largest diameter (microprolactinoma), the chances of definitive cure as a result of surgery alone vary from 62 to 89% depending on the series. Until now, however, there was no mechanism to predict whether total excision of a tumor had been accomplished. To improve the chances of total excision, we compared the peri- and postoperative kinetics of circulating prolactin (PRL) in patients judged to be cured and those not cured. METHODS: The pre-, peri-, and postoperative variations in blood PRL concentrations were determined using assays conducted at 10-minute intervals. Of the 36 patients included in the study, 27 were considered cured (resumption of a normal menstrual cycle within 6 months, PRL concentration at 9 days [mean +/- standard deviation 2.5+/-2.1 ng/ml] and 12 months [4.5+/-2.2 ng/ml] after the operation < 10 ng/ml and normally stimulated by metoclopramide and thyrotropin-releasing hormone [TRH]). Nine patients were not cured (PRL 20+/-15.7 ng/ml at 9 days after surgery, with no response to metoclopramide and TRH). The kinetics of PRL decrease in definitively cured patients were characterized by the following: 1) the initial slope of the curve decreased by at least 11% within the first 10 minutes after resection, and 2) immediate postoperative PRL concentrations were 20 ng/ml or less. CONCLUSIONS: The measurement of the kinetics of PRL decrease during surgery allows the chance of gross-total resection to be successfully predicted less than 25 minutes after excision of the adenoma. Provided an ultrarapid assay is available (the test used in the present study took < 15 minutes), this prognostic index would be useful to make a decision to continue the surgical procedure when the initial PRL slope is judged to be insufficient. Its use may also be extended to other pituitary tumors such as somatotropic adenoma and basophilic adenoma (Cushing's disease).

Utilization of aspirin, quinine and verapamil in the prevention and treatment of scorpion venom intoxication.

Aside from serotherapy, the treatment of scorpion venom intoxication is symptomatic. The aim of this study was to compare the efficacy of drugs usually used in scorpion venom intoxications (atropine, propranolol) to that of other compounds, chosen in light of the pathophysiology of scorpion venom intoxication: dipyridamole, doxapram, quinine formate, lysine-acetyl-salicylate, valproate and verapamil. Using mice, the parameters evaluated were the preventive and therapeutic effects of drugs during experimental venom intoxication by Androctonus australis Hector and one of its toxins AaH 1, and by Buthus occitanus and Tityus serrulatus tunetanus on the other hand. It was found that although most of the drugs used could prolong the survival of the animals, the administration of verapamil and more so that of aspirin or quinine formate led to a 50 to 100% loss of venom and toxin toxicity, depending on the drug and the origin of the venom. In the case of propranolol, doxapram, atropine, dipyridamole and valproate, no or little protection were observed. If these results are confirmed in humans, the systematic use of these drugs could be a simple means for treating scorpion venom intoxication. The problem of scorpion venom intoxication poses a health problem both in the North African Maghreb and in the Americas. As a result of considerable information campaigns, the number of scorpion venom intoxications in Tunisia has dropped from 3000 in 1967 to 1000 per year in the 1980s. Serotherapy has reduced mortality to 0.35%, most deaths occurring in underweight children. In light of the large number of countries in which there is a risk of scorpion venom intoxication in the summertime, however, its prevention and treatment remain a major problem.

Toxicity during early development of the mouse nervous system of a scorpion neurotoxin active on sodium channels.

The lethal effects of scorpion envenomation is due to neurotoxins active on voltage-sensitive sodium channels. Dysfunctions of the peripheral and central nervous systems with neurological manifestations are commonly observed after scorpion stings, specially in young children. Since the neurotoxicity of venom fraction is greatly higher by intracerebroventricular than by subcutaneous injections, a direct effect of venom on CNS cannot be excluded specially in infants where the blood-brain barrier is not fully functional. We investigated the activity of a neurotoxin from the scorpion Androctonus australis hector (AahII) in newborn mice at 3, 7 and 14 days after birth and in adults. Young mice (P3, P7) were more sensitive to AahII injected subcutaneously than were adults, but were less sensitive to intracerebroventricular injection. The affinity of AahII for its receptor site on brain synaptosomes from P3 and P7 mice was slightly higher and the density of the binding sites was half that of adult mice. After subcutaneous injection of [125I]-AahII it was also observed that a small amount of radioactivity was found in brains of neonate mice but not in that of adults. This amount is however extremely lower than the value of the LD50 determined by intracerebroventricular injection. Results are consistent with a peripheral action of AahII and show that its toxic activity changes during the mouse nervous system development.

Cyclosporine A and purinergic receptors in rat kidney.

Previous reports have demonstrated that Cyclosporine A (CyA) chronically administered induces an increase in adenosine plasma concentration by inhibiting adenosine uptake by red blood cells (RBC). We hypothesized that this effect may modulate, by a down regulation, the mRNA expression of adenosine receptors in rat kidney. Since high blood pressure (HBP) is a classical side effect of CyA treatment, nicardipine, a dihydropyridine calcium channel blocker, is often associated with CyA in treatment. To distinguish between the effects of CyA-induced HBP and the effects of CyA by itself, we have evaluated the effects of CyA and/or nicardipine on the mRNA expression of A1 and A2a adenosine receptors. The study was performed on five groups of rats (n= 8) receiving during 21 days either serum saline (0.5 ml i.p), CyA (12 mg/kg/day, i.p), nicardipine (1.2 mg/kg i.p) or nicardipine + CyA. The last (or fifth) group was injected with vehicle (0.5 ml i.p). Blood samples for adenosine assay were collected in the renal artery at day 21, just before the rat kidneys were removed for quantitation of adenosine A1 and A2a mRNA concentration by RT-PCR. We make two conclusions :i) Nicardipine induces a decrease in mRNA expression of A1 but not of A2a adenosine receptors. However, because nicardipine lowered both blood pressure and A1 mRNA expression, it is not possible to conclude if A1 mRNA decrease is implicated in the nicardipine effects on blood pressure.ii) CyA induces an increase in renal artery adenosine concentration and a decrease in mRNA expression of A1 and A2a adenosine receptors.