Stimulation of retinal dopamine biosynthesis in vivo by exogenous tetrahydrobiopterin: relationship to tyrosine hydroxylase activation

Liquid cultures of bone marrow cells enriched for megakaryocytes were assayed for incorporation of 3H-thymidine (3H-TdR) into acid-precipitable cell digests to determine the effect of thrombopoietin on DNA synthesis. As previously described, thrombopoietin was prepared by ammonium sulfate fractionation of pooled plasma obtained from thrombocytopenic rabbits. A control fraction was prepared from normal rabbit plasma. The thrombopoietic activity of these fractions was determined in vivo with normal rabbits as assay animals and the rate of incorporation of 75Se-selenomethionine into newly formed platelets as an index of thrombopoietic activity of the infused material. Guinea pig megakaryocytes were purified using bovine serum albumin gradients. Bone marrow cultures containing 1.5-3.0x104 cells and 31%-71% megakaryocytes were incubated 18 h in modified Dulbecco’s MEM containing 10% of the concentrated plasma fractions from either thrombocytopenic or normal rabbits. In other control cultures, 0.9% NaCl was substituted for the plasma fractions. 3H-TdR incorporation was measured after cells were incubated for 3 h with 1 μCi/ml. The protein fraction containing thrombopoietin-stimulating activity caused a 25%-31% increase in 3H-TdR incorporation over that in cultures which were incubated with the similar fraction from normal plasma and a 29% increase over the activity in control cultures to which 0.9% NaCl had been added. These data suggest that thrombopoietin stimulates DNA synthesis in megakaryocytes and that this tecnique may be useful in assaying thrombopoietin in vitro.

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Contamination of erythropoietin by endotoxin: in vivo and in vitro effects on murine erythropoiesis

Blood ◽

10.1182/blood.v54.1.146.146 ◽

1979 ◽

Vol 54 (1) ◽

pp. 146-158 ◽

Cited By ~ 8

Author(s):

KS Zuckerman ◽

PJ Quesenberry ◽

J Levin ◽

R Sullivan

Keyword(s):

Significant Inhibition ◽

Erythropoietic Activity ◽

Limulus Amebocyte Lysate ◽

Endogenous Erythropoietin ◽

Significant Change ◽

In Vitro Effects ◽

Stimulation Of

Abstract Endotoxin was detected in all erythropoietin preparations tested and was removed from four lots, without loss of erythropoietic activity, by adsorption with limulus amebocyte lysate. Comparison of adsorbed (endotoxin-depleted) and nonadsorbed (endotoxin-containing) erythropoietin preparations demonstrated significant inhibition of CFU- e and BFU-e in vitro by nonadsorbed erythropoietin at concentrations higher than 0.25 U/ml and 2.0 U/ml, respectively. CFU-e and BFU-e were inhibited significantly by readdition in vitro of 10(-5)-10(-3) mug of endotoxin per unit of limulus-adsorbed erythropoietin. Administration of saline or 6 U of nonadsorbed or adsorbed erythropoietin twice a day for 4 days of CF1 mice resulted in reticulocyte counts of 2.1%, 9.9%, and 15.9%, respectively. Nonadsorbed erythropoietin resulted in a 29% decrease in erythropoiesis, a 42% decrease in CFU-e, and a 16% increase in granulopoiesis in the marrow, whereas adsorbed erythropoietin caused a 28% increase in erythropoiesis, no significant change in CFU-e and a 19% decrease in granulopoiesis in the marrow. Both preparations resulted in marked increases in splenic erythropoiesis and granulopoiesis. The effects of adsorbed erythropoietin are similar to those produced following stimulation of hematopoiesis by endogenous erythropoietin. Hemopoietic changes induced by nonadsorbed erythropoietin in vivo and in vitro are affected substantially by contamination of the erythropoietin preparations with endotoxin.

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A Novel α-Conotoxin Identified by Gene Sequencing Is Active in Suppressing the Vascular Response to Selective Stimulation of Sensory Nerves in Vivo†

Biochemistry ◽

10.1021/bi034043e ◽

2003 ◽

Vol 42 (22) ◽

pp. 6904-6911 ◽

Cited By ~ 127

Author(s):

D. W. Sandall ◽

N. Satkunanathan ◽

D. A. Keays ◽

M. A. Polidano ◽

X. Liping ◽

...

Keyword(s):

Gene Sequencing ◽

Sensory Nerves ◽

Vascular Response ◽

Selective Stimulation ◽

Stimulation Of

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Interactions between cholinergic agonists and enteric factors in the regulation of insulin secretion from isolated perifused rat islets

Acta Endocrinologica ◽

10.1530/acta.0.1200702 ◽

1989 ◽

Vol 120 (6) ◽

pp. 702-707 ◽

Cited By ~ 15

Author(s):

Walter S. Zawalich ◽

Kathleen C. Zawalich ◽

Howard Rasmussen

Keyword(s):

Insulin Secretion ◽

Gastric Inhibitory Polypeptide ◽

Moderate Increase ◽

Rat Islets ◽

Insulin Requirements ◽

Isolated Rat Islets ◽

First Phase Insulin Secretion ◽

Sensitizing Effect ◽

Stimulation Of

Abstract. The ability of the cholinergic agonist carbachol to sensitize islets to the action of combined glucose, cholecystokinin and gastric inhibitory polypeptide was determined in isolated rat islets. In response to this combination, peak first phase insulin secretion from control islets averages 85 ± 5 pg · islet−1 · min−1 (mean ± sem) and the insulin secretory rates measured 35–40 min after the onset of stimulation averages 127 ± 34 pg · islet−1 · min−1. A prior 20 min exposure to 1 mmol/l carbachol potentiates the modest insulin stimulatory response to this combination of stimulants: peak first phase release is 354 ± 61 pg · islet−1 · min−1, and release measured 35–40 min after the onset of stimulation is 179 ± 34 pg · islet−1 · min−1. This sensitizing effect of carbachol lasts for at least 40 min and can be duplicated by the natural in vivo agonist acetylcholine. These results demonstrate that cholinergic stimulation of isolated islets primes them to the subsequent stimulatory effect of a moderate increase in the circulating glucose level and to several postulated incretin factors. If operative in vivo, this communications network between cephalic and enteric factors represents a remarkable control system to ensure the release of insulin in amounts commensurate to meet the anticipated and actual insulin requirements for insulin-mediated fuel disposition.

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Oestradiol inhibits collagen breakdown in the involuting rat uterus

Biochemical Journal ◽

10.1042/bj1270705 ◽

1972 ◽

Vol 127 (4) ◽

pp. 705-713 ◽

Cited By ~ 32

Author(s):

Janet N. Ryan ◽

J. Frederick Woessner

Keyword(s):

Cathepsin D ◽

Density Gradient Centrifugation ◽

Post Partum ◽

Gradient Centrifugation ◽

Specific Radioactivity ◽

Rat Uterus ◽

Oestradiol Treatment ◽

Cathepsin D Activity ◽

Stimulation Of

1. The earlier observation (Woessner, 1969) of oestradiol inhibition of collagen breakdown is confirmed and extended. Administration of 100μg of oestradiol-17β/day to parturient rats strongly inhibits the loss of collagen from the involuting uterus. Three experiments show that this effect is due to an inhibition of collagen degradation rather than to a stimulation of collagen synthesis. 2. Uterine collagen was labelled with hydroxy[14C]-proline by the administration of [14C]proline near the end of pregnancy. By 3 days post partum, control uteri lost 83% of their collagen and 90% of their hydroxy[14C]proline. Uteri from oestradiol-treated rats lost only 50% of both total and labelled hydroxyproline, with no decrease in the specific radioactivity of the hydroxyproline. 3. Incorporation of [14C]proline into uterine collagen hydroxyproline in vivo was not affected by oestradiol treatment. 4. Urinary excretion of hydroxyproline was increased in post-partum control rats and decreased in oestradiol-treated rats. 5. An enzyme capable of cleaving 4-phenylazobenzyloxycarbonyl-l-prolyl-l-leucylglycyl- l-prolyl-d-arginine (a substrate for clostridial collagenase) increased in activity in the post-partum uterus and was unaffected by oestradiol treatment. 6. Uterine homogenates digested uterine collagen extensively at pH3.2. This digestion was unaffected by the oestradiol treatment. 7. Lysosomal fractions prepared by density-gradient centrifugation of uterine homogenates contained coincident peaks of cathepsin D activity and peptide-bound hydroxyproline. The cathepsin D and hydroxyproline contents of this peak were unaffected by oestradiol treatment.

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