Cloning, overexpression, purification, and spectroscopic characterization of human S100P

OBJECTIVES: We sought to study the renal circulatory effects of adenosine in patients with chronic congestive heart failure (CHF). BACKGROUND: Renal blood flow (RBF) is often reduced in patients with chronic CHF and may lead to decreased renal function. The cause of reduced RBF is multifactorial and involves systemic as well as local vasoregulatory mechanisms. Stimulation of renal adenosine A1 receptors in animal models has resulted in a significant vasoconstriction of afferent and efferent glomerular arterioles and deterioration of renal function. Although adenosine serum levels have been shown to be elevated in patients with CHF, their effect on the renal circulation in this patient population has not been studied. METHODS: Nine patients with CHF from left ventricular systolic dysfunction were studied. The effects of adenosine at a dose of 10(-5) mol/liter infused directly into the main renal artery on heart rate, renal artery blood pressure, renal artery cross-sectional area (measured by intravascular ultrasound), renal Doppler blood flow velocity (measured by a Doppler flow wire in the renal artery), RBF and renal vascular resistance (RVR) were evaluated. RESULTS: Infusion of adenosine resulted in no significant effect on heart rate or renal artery blood pressure but caused a substantial increase in RVR (11,204 +/- 1,469 to 31,494 +/- 3,911 dynes x s x cm(-5), p = 0.0005), which led to a marked fall in RBF in every patient (mean values 376 +/- 36 to 146 +/- 22 ml/m2, p = 0.0002). These changes in RVR and RBF were associated with no significant change in renal artery cross-sectional area (0.389 +/- 0.040 to 0.375 +/- 0.033 cm2, p = 0.3). CONCLUSIONS: Stimulation of renal adenosine receptors in patients with CHF results in marked renal vasoconstriction that leads to an important reduction in RBF. Lack of change in renal artery cross-sectional area suggests that adenosine affects intrarenal resistance blood vessels rather than large conductance vessels. These results may indicate a rationale for investigation of renal adenosine receptor blockade for enhancement of RBF and improvement of renal function in patients with chronic CHF.     

Modulation of cochlear blood flow by extracellular purines

Humoral adenosine 5'-triphosphate (ATP), adenosine and uridine 5'-triphosphate (UTP) have been shown to have a role in controlling local blood flow in a variety of tissues. The presence of P1 and P2 receptors in the cochlea, and particularly the highly vascular region, the stria vascularis, implies a vasoactive role for these compounds in the inner ear. To test the effect of extracellular purines and pyrimidines on cochlear blood flow, cochleae from anaesthetised guinea-pigs were perfused with ATP (1 microM-10 mM), adenosine (1 microM-10 mM) and UTP (1 mM) in artificial perilymph while blood flow through the cochlea was measured. An acute perilymphatic perfusion technique was established via tubing placed through a hole in the bone overlying scala tympani of the first cochlear turn, with an outlet hole in scala vestibuli of the fourth turn. Blood flow was measured by placing the probe of a laser Doppler blood perfusion monitor on the bone overlying the stria vascularis in the third cochlear turn. ATP and adenosine produced a significant dose dependent increase in cochlear blood flow (28.8-229.0% and 35.8-258.1%, respectively). The effect of ATP (100 microM) on cochlear blood flow was reduced in the presence of reactive blue 2 (1 mM) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (1 mM). The blood flow response to adenosine (10 microM) was reduced in the presence of 1,3-dimethylxanthine (theophylline, 100 microM), but not with either 3,7-dimethyl-1-propargylxanthine (10 microM) or 8-cyclopentyl-1,3-dipropylxanthine (10 microM). UTP did not produce any change in the cochlear blood flow. To determine if the ATP effect was also mediated by adenosine derived from ectonucleotidase activity, the perilymphatic compartment was perfused with either ATP plus theophylline (100 microM) or with the non-metabolisable form of ATP, adenosine 5'-O-(3-thiophosphate) (ATPgammaS, 100 microM). The effect of ATP on cochlear blood flow was unaffected with the inclusion of theophylline while ATPgammaS produced an increase in cochlear blood flow similar to the one observed with ATP. These findings indicate that extracellular ATP and its metabolite adenosine have a modulatory role in cochlear blood flow possibly mediated by both P1 and P2 receptors.     

Cerebral ischemia in gerbils: effects of acute and chronic treatment with adenosine A2A receptor agonist and antagonist

Despite significant progress in understanding of the potential of adenosine A1 receptor-based therapies in treatment of cerebral ischemia and stroke, very little is known about the effect of selective stimulation of adenosine A2A receptors on the outcome of a cerebrovascular arrest. In view of a major role played by adenosine A2 receptors in the regulation of cerebral blood flow, we have investigated the effect of both acute and chronic administration of the selective adenosine receptor agonist 2-[(2-aminoethylamino)-carbonylethylphenylethylamino]-5'-N- ethylcarboxoamidoadenosine (APEC) and antagonist 8-(3-chlorostyryl)caffeine (CSC) on the outcome of 10 min ischemia in gerbils. Acute treatment with APEC improved recovery of postischemic blood flow and survival without affecting neuronal preservation in the hippocampus. Acute treatment with CSC had no effect on the cerebral blood flow but resulted in a very significant protection of hippocampal neurons. Significant improvement of survival was present during the initial 10 days postischemia. Due to subsequent deaths of animals treated acutely with CSC, the end-point mortality (14 days postischemia) in this group did not differ statistically from that seen in the controls. It is, however, possible that the late mortality in the acute CSC group was caused by the systemic effects of brain ischemia that are not subject to the treatment with this drug. Chronic treatment with APEC resulted in a statistically significant improvement in all studied measures. Although chronic treatment with CSC improved postischemic blood flow, its effect on neuronal preservation was minimal and statistically insignificant. Mortality remained unaffected. The results indicate that the acute treatment with adenosine A2A receptor antagonists may have a limited value in treatment of global ischemia. However, since administered CSC has no effect on the reestablishment of postischemic blood flow, treatment of stroke with adenosine A2A receptor antagonists may not be advisable. Additional studies are necessary to elucidate whether chronically administered drugs acting at adenosine A2 receptors may be useful in treatment of stroke and other neurodegenerative disorders.     

Protection of platelet glycoprotein IIb/IIIa receptor complex preserves platelet function during in vitro ventricular assisted circulation

Platelet dysfunction probably contributes to bleeding associated with ventricular assist devices (VADs). Previous evidence suggests that VAD associated platelet dysfunction may be due to dysfunction of the platelet fibrinogen receptor. The purpose of this investigation was to test the hypothesis that selective protection of platelet fibrinogen receptor preserves platelet aggregating ability during in vitro ventricular assisted circulation. Eight in vitro nonpulsatile centrifugal VAD circuits were simulated for four days using 450 ml of fresh human whole blood. Temperature, activated clotting time, pH, PCO2, PO2, Ca2+, and glucose were maintained at physiologic values. Flow was maintained at a constant 2.0 L/min/m2. We examined whole blood platelet aggregation induced by ristocetin, collagen, and adenosine diphosphate (ADP). We added a highly specific reversible inhibitor (MK-383) of the glycoprotein (GP) IIb/IIIa receptor complex before start of circulation to the final four VAD experiments. ADP induced aggregation decreased within the first hour of circulation. Ristocetin and collagen induced aggregation decreased to negligible levels after 10 hours of circulation. With MK-383, ristocetin induced aggregation was preserved. Addition of MK-383 did not alter the decrease of ADP and collagen induced aggregation. These results suggest platelet aggregating ability is maintained with protection of the platelet fibrinogen receptor during in vitro ventricular assisted circulation.     

Effect of adenosine antagonism on metabolically mediated coronary vasodilation in humans

OBJECTIVES: This study was performed to assess the importance of adenosine in mediating metabolic coronary vasodilation during atrial pacing stress in humans. BACKGROUND: Numerous animal studies have examined the role of adenosine in the regulation of coronary blood flow, with inconsistent results. METHODS: The effect of the adenosine antagonist aminophylline (6 mg/kg body weight intravenously) on coronary functional hyperemia during rapid atrial pacing was determined in 12 patients. The extent of inhibition of adenosine vasodilation was assessed using graded intracoronary adenosine infusions before and after aminophylline administration in seven patients. Coronary blood flow changes were measured with a 3F intracoronary Doppler catheter. RESULTS: After aminophylline administration, the increase in coronary flow velocity during adenosine infusions was reduced from 84 +/- 48% (mean +/- SD) to 21 +/- 31% above control values (p < 0.001) at 10 micrograms/min and from 130 +/- 39% to 59 +/- 51% above control values (p < 0.001) at 40 micrograms/min. During rapid atrial pacing under control conditions, coronary blood flow velocity increased by 26 +/- 16%. The flow increment during paced tachycardia after aminophylline (23 +/- 10%) was unchanged from the control value, despite substantial antagonism of adenosine coronary dilation by aminophylline. CONCLUSIONS: These data suggest that adenosine does not play an important role in the regulation of coronary blood flow in response to rapid atrial pacing in humans.     

Acute adenosine treatment is effective in augmentation of ischemic tolerance in muscle flaps in the pig

The objective of the present project was to investigate the efficacy and mechanism of acute (10-minute) adenosine treatment for augmentation of ischemic tolerance in muscle flaps in pigs. Varying doses of adenosine were infused into 28 latissimus dorsi muscle flaps through the axillary artery (0, 0.5, or 2.0 mg per flap) and 22 gracilis muscle flaps through the medial circumflex femoral artery (0, 10, or 20 mg per flap) over 10 minutes. Ten minutes after adenosine infusion, these muscle flaps were subjected to 4 hours of sustained warm global ischemia. In addition, one group of latissimus dorsi muscle flaps (n = 6) received a 10-minute intraarterial adenosine infusion (0.5 mg) at the beginning of reperfusion. Muscle biopsies (n = 4 or 5) for adenosine triphosphate (ATP) analysis were obtained before and after adenosine infusion and at the end of 4 hours of ischemia. The extent of muscle infarction was assessed at 48 hours of reperfusion by the tetrazolium dye staining technique. Muscle blood flow in latissimus dorsi muscle flaps was measured at the end of adenosine infusion (0 or 0.5 mg per flap, n = 8) by the radioactive microsphere (15-microns) technique. It was observed that adenosine, at all doses tested, significantly (p < 0.05) reduced the extent of muscle infarction in latissimus dorsi muscle flaps (control, 40.3 +/- 2.2 percent; 0.5 mg, 20.6 +/- 1.6 percent; 2.0 mg, 18.2 +/- 1 percent) and gracilis muscle flaps (control, 31.0 +/- 1.5 percent; 10 mg, 14.3 +/- 3 percent; 20 mg, 11.6 +/- 1.2 percent). Preischemic adenosine treatment (0.5 mg per flap) was associated with maintenance of a significantly (p < 0.05) higher muscle content of ATP in latissimus dorsi muscle flaps at the end of 4 hours of ischemia compared with saline-treated ischemic controls. Postischemic adenosine treatment did not protect latissimus dorsi muscle flaps against infarction. Furthermore, adenosine treatment did not have any significant effect on mean systemic arterial blood pressure or muscle blood flow in latissimus dorsi muscle flaps. It is concluded that acute (10-minute) preischemic adenosine treatment is effective in augmentation of ischemic tolerance in muscle flaps and that this protective effect of adenosine may be, at least in part, the result of slowing muscle ATP depletion during sustained ischemia. The possible mechanisms of this adenosine-induced energysparing effect are discussed.     

Functional alterations in the pulmonary respiratory system in dogs during alveolar hypoxia with hypercapnia

In acute experiments on 25 dogs, interrelationships of parameters of the small circulation, ventilation, and diffusion were studied during alveolar hypoxia with hypercapnia. Two types of responses of the lung breathing system were revealed. The 1st one involved an increase of the small circulation pressure (by 84%), of volume blood flow (by 42%), of the lung blood volume (by 24%), and of the lung diffusion ability (by 47%). The 2nd type of responses involved an increase of the small circulation pressure on the average by 70%, while the other three parameters practically did not change at all. The combined action of such hemodynamic factors as the increased intravascular pressure and blood flow seem to involve previously inactive vascular areas of the lungs in the circulation. The lung vascular bed of animals with the 1st type of responses is more plastic which can provide a better adaptation of the organism for extreme conditions.     

Vasodilation with adenosine or sodium nitroprusside after coronary artery bypass surgery: a comparative study on myocardial blood flow and metabolism

The effects of adenosine and sodium nitroprusside (SNP) on central hemodynamics and myocardial blood flow and metabolism were investigated postoperatively after elective coronary artery bypass (CABG) surgery in ten sedated and mechanically ventilated patients in the intensive care unit. During three consecutive 15-min periods, SNP (0.8 +/- 0.1 micrograms.kg-1 x min-1), adenosine (88.9 +/- 13.3 micrograms.kg-1 x min-1), and then again SNP (0.7 +/- 0.1 micrograms.kg-1 x min-1) were infused to control postoperative hypertension at a mean arterial pressure of approximately 80 mm Hg. Systemic and pulmonary hemodynamics and global (coronary sinus flow, CSF) as well as regional (great cardiac vein flow, GCVF) myocardial blood flow and metabolic variables were measured. During adenosine infusion, in comparison to SNP, heart rate was unchanged, stroke volume index and cardiac index increased (24% and 32%, respectively), and the systemic vascular resistance index decreased (-26%). Mean pulmonary arterial pressure (24%) as well as pulmonary capillary wedge pressure (27%) and central venous pressure (18%) were higher with adenosine compared to SNP. Adenosine also increased CSF and GCVF (108% and 103%, respectively) without altering the CSF/GCVF flow ratio compared to SNP. Furthermore, adenosine increased the coronary oxygen content (51%) and decreased the arterio-great cardiac vein oxygen content difference (-48%) without changing regional myocardial oxygen consumption, indicating a more pronounced hyperkinetic myocardial circulation compared to SNP. In addition, adenosine infusion decreased arterial PO2 (-11%) and increased the intrapulmonary shunt fraction (57%). The PR interval time of the electrocardiogram was prolonged (12%) and the ST segment was more depressed during adenosine infusion compared to SNP.(ABSTRACT TRUNCATED AT 250 WORDS)     

The treatment of ischemic heart disease in patients with chronic kidney failure

An analysis of the initial type of central hemodynamics and the postoperative period in 177 patients aged older than 70 years having calculous cholecystitis has shown that surgical treatment of patients with the normo- and hyperdynamic types of circulation even with concomitant diseases can give positive results. The least favourable regimen of blood circulation proved to be the hypodynamic type characteristic of patients with pronounced disturbances of homeostasis and/or with recent myocardial infarction.     

Treatment of a maxillary defect following resection of carcinoma

BACKGROUND: Adenosine has been proposed to be a locally produced regulator of blood flow in skeletal muscle. However, the fundamental questions of to what extent adenosine is formed in skeletal muscle tissue of humans, whether it is present in the interstitium, and where it exerts its vasodilatory effect remain unanswered. METHODS AND RESULTS: The interstitial adenosine concentration was determined in the vastus lateralis muscle of healthy humans via dialysis probes inserted in the muscle. The probes were perfused with buffer, and the dialysate samples were collected at rest and during graded knee extensor exercise. At rest, the interstitial concentration of adenosine was 220+/-100 nmol/L and femoral arterial blood flow (FaBF) was 0.19+/-0.02 L/min. When the subjects exercised lightly, at a work rate of 10 W, there was a markedly higher (1140+/-540 nmol/L; P<0.05) interstitial adenosine concentration and a higher FaBF (2.22+/-0.18 L/min; P<0.05) compared with at rest. When exercise was performed at 20, 30, 40, or 50 W, the concentration of adenosine was moderately greater for each increment, as was the level of leg blood flow. The interstitial concentrations of ATP, ADP, and AMP increased from rest (0.13+/-0.03, 0.07+/-0.03, and 0.07+/-0.02 micromol/L, respectively) to exercise (10 W; 2.00+/-1.32, 2.08+/-1.23, and 1.65+/-0.50 micromol/L, respectively; P<0.05). CONCLUSIONS: The present study provides, for the first time, interstitial adenosine concentrations in human skeletal muscle and demonstrates that adenosine and its precursors increase in the exercising muscle interstitium, at a rate associated with intensity of muscle contraction and the magnitude of muscle blood flow.     

Blockade of cerebral blood flow response to insulin-induced hypoglycemia by caffeine and glibenclamide in conscious rats

The possibility that adenosine and ATP-sensitive potassium channels (KATP) might be involved in the mechanisms of the increases in cerebral blood flow (CBF) that occur in insulin-induced hypoglycemia was examined. Cerebral blood flow was measured by the [14C]iodoantipyrine method in conscious rats during insulin-induced, moderate hypoglycemia (2 to 3 mmol/L glucose in arterial plasma) after intravenous injections of 10 to 20 mg/kg of caffeine, an adenosine receptor antagonist, or intracisternal infusion of 1 to 2 mumol/L glibenclamide, a KATP channel inhibitor. Cerebral blood flow was also measured in corresponding normoglycemic and drug-free control groups. Cerebral blood flow was 51% higher in untreated hypoglycemic than in untreated normoglycemic rats (P < 0.01). Caffeine had a small, statistically insignificant effect on CBF in normoglycemic rats, but reduced the CBF response to hypoglycemia in a dose-dependent manner, i.e., 27% increase with 10 mg/kg and complete elimination with 20 mg/kg. Chemical determinations by HPLC in extracts of freeze-blown brains showed significant increases in the levels of adenosine and its degradation products, inosine and hypoxanthine, during hypoglycemia (P < 0.05). Intracisternal glibenclamide had little effect on CBF in normoglycemia, but, like caffeine, produced dose-dependent reductions in the magnitude of the increases in CBF during hypoglycemia, i.e., +66% with glibenclamide-free artificial CSF administration, +25% with 1 mumol/L glibenclamide, and almost complete blockade (+5%) with 2 mumol/L glibenclamide. These results suggest that adenosine and KATP channels may play a role in the increases in CBF during hypoglycemia.     

Adenosine transport inhibition ameliorates postischemic hypoperfusion in pigs

Cerebral ischemia is often followed by a period of delayed hypoperfusion that may contribute to tissue injury. We tested the hypothesis that augmentation of interstitial adenosine can improve tissue perfusion under this condition 10 min global ischemia was produced in two groups of isoflurane-anesthetized newborn pigs by occlusion of subclavian and brachiocephalic arteries, and changes in local cortical blood flow and cortical interstitial purine metabolites were measured using the combined hydrogen clearance-microdialysis technique. In one group, the dialysis probe was perfused with artificial cerebrospinal fluid buffer containing nitrobenzyl-thioinosine (NBT1, 100 mumol/l), a competitive inhibitor of adenosine transport. In the untreated group (n = 9), baseline cortical blood flow (39 +/- 3 ml/min/100 g) was depressed by 51 +/- 5% and 42 +/- 6% at 40 and 60 min, respectively, of postischemic reperfusion. NBTI increased baseline interstitial adenosine levels 2.4-fold which increased baseline cortical blood flow 1.5-fold to 60 +/- 4 ml/min/100 g, and increased both absolute adenosine levels as well as adenosine as a percentage of total purine metabolites throughout ischemia and reperfusion. As a result, the extent of postischemic hypoperfusion was significantly lessened in NBTI-treated animals (n = 9), with reductions in cortical blood flow of only 28 +/- 3% and 24 +/- 5% at 40 and 60 min of reperfusion, respectively. These results indicate that inhibition of adenosine transport by NBTI elevates interstitial adenosine concentration during and following cerebral ischemia, and concomitantly improves cortical perfusion in the post-ischemic period. The latter effect may contribute to the documented neuroprotective efficacy of adenosinergic therapy in cerebral ischemia.     

Hemorrhages in muscles of broiler chickens: the relationships among blood variables at various rearing temperature regimens

Hemorrhages in muscle tissue can be considered as major quality defects of broiler carcasses. They can be induced by stunning, especially electrical stunning. The underlying mechanism, however, is considered to be multifactorial. In this study, the effect of blood circulation disturbances on the severity of hemorrhages induced by electrical stunning was investigated. The disturbances were evoked in two genetically different, fast-growing broiler strains, Ross and Hybro, by rearing the broilers at low ambient temperatures. The broilers were slaughtered by two different electrical stunning methods. Broilers reared at low temperatures showed changes in blood variables and heart weight known to be associated with blood circulation disturbances. There was no effect of rearing temperature on hemorrhage severity. Ross broilers, being the most susceptible to low temperatures, had less severe hemorrhages than Hybro broilers. There was, however, a clear effect of the stunning method on hemorrhage severity. Whole body stunning caused more severe hemorrhages than head stunning in thigh and breast muscles. These results suggest that factors interfering with blood circulation have little or no effect on the occurrence of hemorrhages induced by electrical stunning.     

Comparison of interstitial fluid and coronary venous adenosine levels in in vivo porcine myocardium

There are numerous reports of interstitial fluid (ISF) and coronary venous adenosine measurements in isolated perfused hearts. This study was designed to simultaneously compare ISF and coronary venous adenosine concentrations during various interventions in in vivo porcine myocardium. In anesthetized, open-chest pigs, ISF adenosine, inosine, and hypoxanthine were sampled with cardiac microdialysis. Coronary sinus or venous purines were sampled with a metabolism-stop solution. During basal conditions, ISF adenosine was greater than coronary venous adenosine, but vascular inosine and hypoxanthine were greater than corresponding ISF levels. Dobutamine (20 micrograms/kg/min, i.v.) and systemic hypoxia produced three- and two-fold increases in ISF adenosine, but had no significant effect on coronary sinus adenosine concentration. Hypoxia, but not dobutamine, increased coronary sinus total purines 50%. In contrast to these interventions, intracoronary adenosine infusion (0.5-50 micrograms/kg/min) was associated with significantly greater coronary venous adenosine concentrations than ISF levels. Only during a coronary artery occlusion/reperfusion protocol were ISF and coronary venous adenosine concentrations comparable. The results of this study thus provide in vivo evidence of the powerful endothelial and red blood cell metabolic barriers to both exogenous and endogenous adenosine. These results also illustrate the differences in adenosine concentrations in the ISF and vascular spaces.     

Impaired endothelium-dependent relaxation after cardiac global ischemia and reperfusion: role of warm blood cardioplegia

OBJECTIVES: Experiments were designed to determine whether coronary endothelial dysfunction after cardiac global ischemia and reperfusion could be prevented by warm blood cardioplegic solution. BACKGROUND: The coronary endothelium produces endothelium-derived relaxing factor (EDRF) to prevent vasospasm and thrombosis. After ischemia and reperfusion, endothelium-dependent relaxation (EDR) is diminished as a result of G-protein dysfunction. METHODS: Dogs were exposed to extracorporeal circulation in 37 degrees C (group 1) or 28 degrees C (groups 2 and 3). The heart was ischemic for 120 min while continuous warm blood cardioplegic solution (group 1) or intermittent cold (4 degrees C) crystalloid cardioplegic solution was not used in group 3 animals. The heart was then allowed to function for 60 min of reperfusion. RESULTS: Endothelium-derived relaxation in response to acetylcholine, adenosine diphosphate and sodium fluoride of the coronary rings of group 1 was significantly different from that of groups 2 and 3 but was not significantly different from that of group 4. In contrast, EDR in response to the receptor-independent calcium ionophore agonist A23187 was not significantly different between the four groups. Scanning electron microscopic studies showed that platelet adhesion and aggregation, area of microthrombi, disruption of endothelial cells and separation of the intercellular junction could be found in coronary segments of groups 2 and 3 but not in vessels of groups 1 and 4. CONCLUSIONS: These experiments suggest that cardiac global ischemia and reperfusion impair receptor-mediated release of EDRF from the coronary endothelium with G-protein dysfunction. This type of coronary endothelial dysfunction can be prevented by continuous anterograde infusion of warm blood cardioplegic solution during global ischemia.     

The characteristics of the effect of obzidan on the cardiac hemodynamics in patients with an artificial pacemaker when used one time and over a course of treatment

ECG investigations of cardiodynamics were performed in 47 patients subjected to isolated ventricular electrocardiostimulation on obsidan treatment. The drug was given in a single dose or in a course. Cardiodynamic effects were evaluated in 3 groups of patients: with hyperkinetic, eukinetic and hypokinetic circulation (17, 19 and 11 patients, respectively). Cardiohemodynamic effects of obsidan are shown to depend on type of circulation and features of intracardiac hemodynamics (fixed cardiac rhythm, atrioventricular dissociation, pathological ventricular asynchronism, valvular blood regurgitation). This potentiates cardiodepressive effects of obsidan in patients with hypokinetic circulation who experience deterioration of cardiac insufficiency.     

Effect of systemic corticoid and antihistamine alone or in combination on elements of the response to a two dose nasal allergen challenge

Adenosine, an endogenous vasodilator, induces a cerebral vasodilation at hypotensive infusion rates in anaesthetized humans. At lower doses (< 100 micrograms kg-1 min-1), adenosine has shown to have an analgesic effect. This study was undertaken to investigate whether a low dose, causing tolerable symptoms of peripheral vasodilation affects the global cerebral blood flow (CBF). In nine healthy volunteers CBF measurements were made using axial magnetic resonance (MR) phase images of the internal carotid and vertebral arteries at the level of C2-3. Quantitative assessment of CBF was also obtained with positron emission tomography (PET) technique, using intravenous bolus [15O]butanol as tracer in four of the subject at another occasion. During normoventilation (5.4 +/- 0.2 kPa, mean +/- s.e.m.), the cerebral blood flow measured by magnetic resonance imaging technique, as the sum of the flows in both carotid and vertebral arteries, was 863 +/- 66 mL min-1, equivalent to about 64 +/- 5 mL 100 g-1 min-1. The cerebral blood flow measured by positron emission tomography technique, was 59 +/- 4 mL 100 g-1 min-1. All subjects had a normal CO2 reactivity. When adenosine was infused (84 +/- 7 micrograms kg-1 min-1.) the cerebral blood flow, measured by magnetic resonance imaging was 60 +/- 5 mL 100 g-1 min-1. The end tidal CO2 level was slightly lower (0.2 +/- 0.1 kPa) during adenosine infusion than during normoventilation. In the subgroup there was no difference in cerebral blood flow as measured by magnetic resonance imaging or positron emission tomography. In conclusion, adenosine infusion at tolerable doses in healthy volunteers does not affect global cerebral blood flow in unanaesthetized humans.     

Effect of intracoronary estrogen on coronary collateral blood flow velocity

The effect of estrogen on collateral circulation has not been previously investigated. We assessed the acute effect of estradiol on collateral blood flow velocity with the Flowire during percutaneous transluminal coronary angioplasty and found that intracoronary estradiol decreased collateral blood flow velocity compared with controls.     

Modulation of erythropoietin production by selective adenosine agonists and antagonists in normal and anemic rats

Hypoxia or anemia is the fundamental stimulus for erythropoietin (EPO) production. Recent in vitro studies suggest that EPO secretion in response to hypoxia is regulated by adenosine in the kidney. In order to examine the in vivo effect of adenosine on EPO production, we determined the effects of adenosine receptor agonists and antagonists on serum EPO concentration in normal and anemic rats. In normal rats, intravenous injection of adenosine agonists (NECA, CHA and CGS-21680) dose-dependently stimulated EPO production. Pretreatment with KW-3902, an adenosine A1 antagonist with modest A2b antagonistic action, or KF17837, an adenosine A2a antagonist, inhibited the NECA (0.1 mg/kg, i.v.)-stimulated EPO production. Anemic hypoxia, induced by 2% (v/w body weight) blood withdrawal, increased serum EPO concentration from 38 +/- 2 to 352 +/- 76 mU/ml, with the increased serum adenosine concentration in the renal vein. KF17837 (0.1 mg/kg, i.v.), but not KW-3902 (0.1 mg/kg, i.v.), inhibited the anemic hypoxia-induced increase in EPO production. The present findings support the notion that adenosine mediates the EPO production in response to hypoxia in the kidney.     

Processing of adenosine receptor agonists in rat and human whole blood

A stability study of adenosine receptor agonists in rat and human whole blood was performed. The compounds were incubated at 37 degrees in fresh blood, and aliquots of the incubation mixture were hemolyzed at regular time intervals and analyzed with HPLC. N6-cyclopentyladenosine (CPA) and N6-cyclobutyladenosine (CBA) were degraded, whereas N6-cyclohexyladenosine, N6-cycloheptyladenosine and N6-sulfophenyladenosine were not. 2-Chloroadenosine had a half-life very similar to that of CPA. However, the 2'-, 3'-, and 5'-deoxyribose derivatives of CPA remained intact. The nucleoside transport inhibitor nitrobenzylthioinosine attenuated CBA and CPA metabolism in rat blood as did the inhibitor of adenosine deaminase erythro-9-(2-hydroxy-3-nonyl)adenine, albeit at relatively high concentrations. Complete blockade of CBA and CPA degradation was achieved by a preincubation of rat and human blood with the adenosine kinase (AK) inhibitor 5'-amino-5'-deoxyadenosine. We conclude that the two adenosine analogues are metabolized by AK both in rat and in human whole blood.