Erythropoietin and blood pressure.
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Angiotensin II↗
Biomedical subjects
W Jelkmann
Publications and source records attributed to W Jelkmann.
The complete nucleotide sequence of plum pox virus RNA.
The complete nucleotide sequence of the RNA of an aphid non-transmissible plum pox virus (PPV-NAT) isolate has been determined from five overlapping cDNA clones. cDNA prepared by primer extension was used to determine the 5' terminus. The assembled RNA is 9741 nucleotides in length, excluding a 3' terminal poly(A) sequence. One large open reading frame starts at nucleotide positions 36 to 38 and is terminated with an UAG codon at positions 9522 to 9524. The putative start codon is located at positions 147 to 149. The encoded polyprotein has a predicted Mr of 353.8K. Comparison of cistrons from tobacco vein mottling virus and tobacco etch virus with those predicted for PPV-NAT indicated a similar genome organization. A highly conserved sequence of 12 nucleotides was found in the 5' non-coding region of these three potyviruses. The potential polyadenylation signal from yeast (UAUGU) was found in the 3' non-coding region of PPV-NAT and several other members of the potyvirus group.
Amino Acid Sequence↗
Erythropoietin/haemoglobin relationship in leukaemia and ulcerative colitis.
The erythropoietin level was measured, by bioassay in polycythaemic mice, in the serum of anaemic patients suffering from different types of leukaemia. Comparative measurements were carried out in patients with ulcerative colitis. Serum erythropoietin was less well-correlated with the haemoglobin concentration in leukaemia than in ulcerative colitis. While serum erythropoietin did not exceed 200 mU/ml in patients with ulcerative colitis (lowest blood haemoglobin concentration 56 g/l), several of the leukaemic patients had serum erythropoietin levels above 500 mU/ml at comparable degrees of anaemia. Bone marrow biopsy showed that erythropoiesis was severely impaired in the leukaemic patients whose erythropoietin values were relatively high. These findings are in accord with the hypothesis that the plasma level of erythropoietin depends not only on the haemoglobin concentration of the blood but also on the bone marrow responsiveness to the hormone.
Adolescent↗
A new stable epithelial cell line (RK-L) from normal rat kidney.
A stable epithelial cell line has been established from the kidneys of a normal Sprague-Dawley rat. This line, termed RK-L, has a high proliferative capacity (minimal doubling time 12.3 h) and can be grown in medium containing 1% fetal bovine serum. Thus far, the line has been carried through more than 60 serial passages. The RK-L cells were found to display similarities with kidney tubule cells. Using light microscopy, confluent cultures were seen as pavement-like monolayers forming domes, which are thought to result from transepithelial fluid transport. Electron microscopy revealed polarized cells that had microvilli on the apical surface, junction complexes in the apical part of the lateral cell membrane, and a basal lamina-like layer. Pinocytotic activity was indicated by infoldings of the apical plasma membrane and the formation of vesicles. The RK-L line should prove useful for investigations of kidney tubule transport mechanisms.
Animals↗
Lowered plasma erythropoietin in hypoxic rats with kidney tubule lesions.
The role of the kidney tubules in the renal formation of erythropoietin is incompletely understood. Therefore, the capability to produce erythropoietin in response to hypoxia was studied in rats with tubular lesions. Nephron damage was induced in two different ways. First, rats were treated with the nephrotoxic aminoglycoside gentamicin (67.5 mg/kg and day) for 14 days. The animals were then subjected to simulated altitude (6,800 m) for 6 h. The resulting plasma erythropoietin concentration was significantly lower (0.5 IU/ml) than in saline treated control rats exposed to hypoxia (1.0 IU/ml). Second, unilateral hydronephrosis was induced by ureteral ligation. The contralateral kidney was removed immediately before the animals were exposed to simulated altitude for 6 h. The plasma erythropoietin concentration in the ureter-ligated rats did not increase above the value (0.3 IU/ml) in hypoxia exposed anephric rats. These results indicate that the production of erythropoietin is reduced following tubular injury. Tubule cells may directly produce the hormone or interfere with the O2-sensing mechanisms controlling its synthesis. The latter hypothesis would seem to be supported by our failure to demonstrate in vitro erythropoietin production by the two established kidney tubule cell lines, LLC-PK1 and PK-15.
Altitude↗
A comparison of the effects of renal artery constriction and anemia on the production of erythropoietin.
It is generally assumed that the O2 supply to the kidneys is the major determinant of the synthesis of erythropoietin (Ep). In the present study, the O2 supply of the kidneys of rats was lowered by the reduction of renal blood flow (rbf). Plasma Ep was determined after about 18 h of bilateral application of Goldblatt clips with graded inner diameters. The results were compared to findings in anemic rats, in which the systemic O2 supply was lowered by exchange transfusion of blood with plasma. We found a linear correlation between Ep levels in plasma and the degree of reduction of rbf. However, there was an exponential relationship between Ep levels and the concentration of hemoglobin in blood. In addition, the elevation of plasma Ep was only moderate, when rbf was reduced (maximum 0.07 IU Ep/ml plasma). The increase in Ep concentration was much more pronounced in anemia (up to about 7 IU Ep/ml plasma). From these results it may be concluded that decreasing oxygen supply to the kidney through reduction in renal blood flow (ischemic hypoxia) is less effective in increasing erythropoietin production than reducing the hemoglobin concentration (anemic hypoxia). The possibility must be considered that the increase in renal production of erythropoietin due to anemic hypoxia is triggered by one or more extrarenal signals.
Anemia↗
Prostaglandin E2 and atriopeptin III oppose the contractile effect of angiotensin II in rat kidney mesangial cell cultures.
Effects of vasoconstrictory and of dilatory hormones were studied on the contractile activity of cultured rat kidney mesangial cells. By phase contrast microscopy, a rapid contraction was seen of most cells treated with angiotensin II (10(-6) - 10(-10) mol/L), which was sometimes followed by autonomous relaxation after 10 to 20 min. Prostaglandin E2 and atriopeptin III prevented the contractile effect of angiotensin II in a dose-dependent manner. Angiotensin II, but not atriopeptin III, stimulated prostaglandin E2 synthesis in mesangial cell cultures.
Angiotensin II↗
Effect of PO2 on prostaglandin E2 production in renal cell cultures.
There is evidence both from in vivo and in vitro studies which suggests that hypoxia stimulates the synthesis of prostanoids in some tissues. In the present study, the in vitro production of prostaglandin E2 (PGE2) was studied in three different renal cell lines incubated at various PO2 values between 143 and 3 mm Hg for 24 h. In rat kidney mesangial cell cultures, PGE2 production increased up to 99 ng PGE2/mg protein at 7 mm Hg O2, compared to 52 ng/mg at 143 mm Hg O2, but was lowered at 26 ng/mg at 3 mm Hg O2. PGE2 production by the pig kidney tubule cell lines LLC-PK1 and PK-15 was insensitive to PO2 changes. Because PGE2 production is known to be Ca2+-dependent and was indeed stimulated by the Ca-ionophore A 23187, effects of hypoxia on 45Ca2+-fluxes were also studied. In none of the 3 cell lines, net 45Ca-influx was altered after incubation at low PO2. However, net 45Ca-efflux increased during hypoxic incubation of mesangial cells possibly as a result of intracellular Ca-mobilization. These results indicate that hypoxia stimulates PGE2 synthesis in mesangial but not in tubule cell cultures. However, at very low PO2 values, or anoxia, the formation of cyclic endoperoxides from arachidonic acid may be lowered. Since mesangiocytes are smooth muscle-like cells, the hypoxia-induced synthesis of relaxing prostanoids could play a role in the regulation of smooth muscle tone.
Animals↗
Dependence of erythropoietin production on blood oxygen affinity and hemoglobin concentration in rats.
Plasma erythropoietin titers (Ep) were compared in rats subjected to different kinds of systemic hypoxia. Ep increased exponentially, when hypoxia was induced by exposure to simulated altitude (from less than 0.025 IU Ep/ml plasma at sea-level up to 3.65 IU Ep/ml at 7000 m). An acute increase in the O2 affinity of blood augmented Ep production in normal rats but not in rats exposed to hypobaria. Ep also rose exponentially when isovolemic anemia was induced (e.g., 0.5 IU Ep/ml plasma were found at 7 g Hb/dl blood). When the same reduction in blood O2 carrying capacity was produced by CO-inhalation (0.1% CO in air), Ep increased to 5.57 IU/ml plasma. This very high value was considered to be partly due to the very high O2 affinity of carboxyhemoglobin. These results indicate that a left shift in the hemoglobin-O2 dissociation curve produces a stimulation of Ep production, particularly, when the O2-carrying capacity of blood is lowered.
Anemia↗
Renal erythropoietin: properties and production.
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Animals↗
Erythropoietin research, 80 years after the initial studies by Carnot and Deflandre.
The discovery and present state of knowledge of the specific hormonal mechanism controlling erythropoiesis are briefly reviewed. 80 years ago, Carnot and Deflandre postulated the existence of a humoral erythropoietic factor ('hémopoïétine') produced in response to anemia. The general approval of this concept required almost 50 years, when the factor was recognized to be a glycoprotein hormone and termed 'erythropoietin'. Very recently, human erythropoietin has been purified and its amino acid sequence been identified. The hormone is mainly of renal origin. Its production is stimulated by tissue hypoxia of different causes. The mechanism of O2 sensing and the exact site of erythropoietin synthesis in the kidney still remain to be clarified.
Animals↗
Erythropoietin production in cultures of rat renal mesangial cells.
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Animals↗
Erythropoietin production by fetal mouse liver cells in response to hypoxia and adenylate cyclase stimulation.
This study was done to investigate aspects of control of extrarenal erythropoietin (Ep) production. To this end we studied the effects of three stimuli of renal Ep production in the adult, i.e. hypoxia, cobalt, and activation of adenylate cyclase on Ep generation by cultured fetal mouse liver cells. The fetal liver was taken as a model for extrarenal Ep production because this organ is considered the predominant site of extrarenal Ep production. We found that Ep production by the cells increased as the oxygen concentration was decreased in the incubation atmosphere from 20% to 1%. Cobalt (10(-4)-10(-5) M) had no effect on Ep production. Activation of adenylate cyclase by forskolin (10(-5) M) or isoproterenol (10(-5) M) greatly enhanced Ep production. These findings indicate that the Ep-stimulating effect of cobalt is specific for the kidney. However, oxygen depletion and activation of adenylate cyclase seem to be more general stimuli in Ep-producing cells. Furthermore we found that Ep production in hypoxia correlated with lactate formation in the cultured liver cells. This finding suggests that Ep production in fetal livers under hypoxic conditions parallels the shift from aerobic to anaerobic cellular energy metabolism.
Adenylyl Cyclases↗
Erythropoietin production in normoxic and hypoxic rats with increased blood O2 affinity.
Effects of an acute increase in blood O2 affinity on erythropoietin production were studied in normoxic and hypoxic male rats. Blood O2 affinity was increased by exchange-transfusion with blood from sodium cyanate treated rats. P50 was lowered to 27.6 torr (pH 7.4, PCO2 = 40 torr, 37 degrees C) in the recipients compared to 41.8 torr in control rats exchange transfused with normal blood. Hypoxia was induced by exposure to simulated high altitude (4750 or 7000 m) for 16 h. Erythropoietin was determined by in vivo bioassay. In rats with normal blood O2 affinity, plasma erythropoietin was undetectable at 300 m, 0.26 +/- 0.10 U/ml at 4750 m (mean +/- SEM; n = 7), and 3.52 +/- 0.58 U/ml at 7000 m (n = 10). Plasma erythropoietin titers were significantly enhanced in rats with high blood O2 affinity at 300 m (0.05 +/- 0.01 U/ml; n = 4) and moderately increased at 4750 m (0.57 +/- 0.12 U/ml; n = 7), but unchanged at 7000 m (3.88 +/- 0.74 U/ml; n = 10). These results indicate that a high blood O2 affinity reduces the O2 delivery to the cells controlling erythropoietin production in normoxia and moderate hypoxia. However, this is offset at severe hypoxia most likely by an improved O2 loading to the blood.
Altitude↗
Hypoxia enhances prostaglandin synthesis in renal mesangial cell cultures.
In view of recent findings which suggest that renal prostaglandins mediate the effect of hypoxia on erythropoietin production, we have studied whether hypoxia is a stimulus for in vitro prostaglandin synthesis. Studies were carried out in rat renal mesangial cell cultures which produce erythropoietin in an oxygen-dependent manner. Production rates of PGE2 and in specified samples also of 6-keto-PGF1 alpha, as a measure of PGI2, and PGF2 alpha were determined by radioimmunoassay after incubation at either 20% O2 (normoxic) or 2% O2 (hypoxic) in gas permeable dishes for 24 hrs. Considerable variation in PGE2 production was noted among independent cell lines. PGE2 production appeared to be inversely correlated to the cellular density of the cultures. In addition, PGE2 production was enhanced in hypoxic cell cultures. The mean increase was 50 to 60%. PGF2 alpha and 6-keto-PGF1 alpha increased by about the same rate. These results indicate that hypoxia is a stimulus for in vitro prostaglandin production.
6-Ketoprostaglandin F1 alpha↗
Role of prostaglandins in hypoxia-stimulated erythropoietin production.
The role of prostaglandins in the mediation of hypoxia-stimulated erythropoietin (Ep) production by cultured rat renal mesangial cells was examined. It was found that an increase in prostaglandin E2 (PGE2) production accompanied the rise in Ep due to hypoxia (2% O2). The hypoxia-stimulated increase in Ep production was abolished in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M). When PGE2 (10(-6) M was added simultaneously with indomethacin, however, no diminution in hypoxia-stimulated Ep production was observed. Addition of arachidonic acid (AA, 10(-5) M), PGE2 (10(-6) M), or PGI2 (10(-4) M) enhanced Ep production under normoxic conditions (20% O2), while PGF2 alpha (10(-6) M) had no effect on Ep production. AA, PGE2, and PGI2 were found to stimulate adenosine 3',5'-cyclic monophosphate formation by the cultured mesangial cells. Enhancement of adenylate cyclase activity by forskolin (10(-5) M) also increased Ep production in the cell cultures. Our results suggest that hypoxia-stimulated Ep production by cultured mesangial cells is mediated by prostaglandins with subsequent stimulation of adenylate cyclase activity.
Adenylyl Cyclases↗
Activity in fetal bovine serum that stimulates erythroid colony formation in fetal mouse livers is insulinlike growth factor I.
In the present study, the erythropoietic activity of fetal serum was characterized. Using fetal bovine serum (FBS) as a source of the erythropoietic activity and serum-free cultures of fetal mouse livers (FMLC assay) as a detection system, we found that FBS stimulated colony formation from late erythroid progenitor cells (CFU-E) in a dose-dependent fashion. The slope of the dose-response curve, however, was significantly different from that for erythropoietin (Ep), the best-characterized erythropoietic activity so far. The erythropoietic activity of FBS was found in the 120-160- and 40-70-kD range at neutral pH. In the presence of 1 M acetic acid, however, the erythropoietic activity had an apparent molecular mass between 3 and 13 kD. From ion exchange experiments with DEAE-cellulose, the isoionic point of the activity was estimated to about pH 5. Furthermore, the erythropoietic activity of FBS was found to be co-eluted on Sephadex G-150 with the binding proteins of insulinlike growth factors (IGF). The IGF I concentration determined by radioimmunoassay was 70 ng IGF I/ml. The Ep activity of FBS was less than 5 mU/ml when determined with the posthypoxic polycythemic mouse assay for Ep. These results suggest that the erythropoietic activity of FBS is related to IGF and not to Ep. The erythropoietic activity of FBS was abolished by an antiserum against IGF I. Furthermore, IGF I was a factor of approximately 40 more potent than IGF II in stimulating erythroid colony formation. All of these findings suggest that the erythropoietic activity of FBS is IGF I.
Animals↗
Oxygen binding and acid base status of the blood from the freshwater turtle, Phrynops hilarii.
Oxygenation studies with the whole blood of Phrynops hilarii show a P50 of 38 torr at extracellular pH (pHe) of 7.4 which corresponds to an intracellular pH (pHi) of 7.05 at 25 degrees C. The blood CO2 Bohr effect was -0.56 when related to pHi. pHi is related to pHe by the following equation: pHi = 0.75.pHe + 1.54 (r = 0.99); pHi = 0.72. pHe + 1.72 (r = 0.96) at 10 and 25 degrees C respectively. Blood pHe, for 25 degrees C, was 7.519 +/- 0.254 (n = 6). Blood gas partial pressures were: pCO2 = 25.8 +/- 3.8 torr (n = 6); pO2 = 61.7 +/- 21.2 torr (n = 6). The major red cell phosphates, in mmole/l erythrocytes, n = 6, were: ATP (3.66 +/- 0.86); GTP (0.53 +/- 0.28); 2.3-DPG (0.32 +/- 0.12) and inorganic phosphates (2.00 +/- 0.35). The plasma inorganic ion composition, n = 6, was, in mEq/l: K+ (3.04 +/- 0.40); Na+ (148.4 +/- 12.6); Ca2+ (4.75 +/- 1.32); Cl- (106.6 +/- 5.0). Additional blood parameters of interest (n = 6) were: lactate (2.07 +/- 1.72 mM in plasma); erythrocytes/mm3 (416 X 10(3) +/- 4.6 X 10(3)); leucocytes/mm3 (44636 +/- 2618); haematocrit (%) (14.5 +/- 3.6); haemoglobin, g/dl (3.2 +/- 0.5); plasma protein g/dl (4.4 +/- 0.4); osmolarity (293 +/- 10 mOsm/l). The non-bicarbonate buffer value was -22.6 mmol/kg H2O/pH. For a constant CO2 content, delta pHe/delta t = 0.0141 +/- 0.002 (n = 18) and delta pHi/delta t = 0.0157 +/- 0.003 (n = 18).
Acid-Base Equilibrium↗