adenosine-5--(n-ethylcarboxamide) and Anemia

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.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Analysis of Variance; Anemia; Animals; Erythropoietin; Hematocrit; Hypoxia; Kinetics; Male; Nephrectomy; Phenethylamines; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Wistar; Time Factors; Xanthines

A method which involves Percoll gradient centrifugation, is described for separating rabbit reticulocytes from other blood cells, including erythrocytes. This permits a quantitative comparison of the adenylate cyclase activity of reticulocyte membranes which had been induced either by bleeding (30% reticulocytosis) or by repeated injections of phenylhydrazine (90% reticulocytosis). Adenylate cyclase activity was greatly impaired on exposure to the hemolytic agent; total activity was reduced about 20-fold. However, a more selective loss was observed in terms of hormonal stimulation. Prostaglandin E1 was 2-fold more effective than either sodium fluoride or Forskolin in stimulating the enzyme from bled reticulocytes, whereas it was 3-fold less effective than either fluoride or Forskolin in the case of membranes from animals which had been exposed to phenylhydrazine. A stimulatory adenosine receptor was detectable only in reticulocytes which had not been treated with the hemolytic agent. These studies suggest that purified reticulocytes from bled animals represent the most suitable model system in which to study the maturation of red blood cells.

Topics: 1-Methyl-3-isobutylxanthine; Adenosine; Adenosine-5'-(N-ethylcarboxamide); Adenylyl Cyclases; Anemia; Animals; Drug Antagonism; Erythrocyte Membrane; Erythrocytes; Female; Kinetics; Phenylhydrazines; Rabbits; Reticulocytes; Vasodilator Agents