Demonstration of burst-promoting activity of recombinant human GM-CSF on circulating erythroid progenitors using an assay involving the delayed addition of erythropoietin

We demonstrate through the use of an in vitro assay involving the delayed addition of erythropoietin that human recombinant GM-CSF, cloned from a mature T cell line, Mo, clearly has burst-promoting activity (BPA) on peripheral blood erythroid progenitors at picomolar concentrations. Delay for up to 72 hours of the addition of erythropoietin to semi-solid methylcellulose cultures of concentrated peripheral blood progenitors minimizes or eliminates BPA-independent erythroid colony formation with little loss of BPA-dependent erythroid colony formation. This assay will prove useful in accurately detecting sources of BPA.     

Heparin does not interfere with prostacyclin and prostaglandin D2 binding to platelets

Heparin has been reported to antagonize the platelet antiaggregating activity of prostacyclin (PGI2) and prostaglandin D2 (PGD2). To investigate whether heparin interferes with PGI2 and/or PGD2 binding to the specific membrane platelet receptors, the number and the affinity of binding sites for tritiated PGI2 and PGD2 were determined in 8 healthy subjects (aged 25-32; 4 for PGI2 and 4 for PGD2 studies) in the absence and in the presence of heparin. Preliminary aggregation tests indicated that the heparin concentration tested (2 I.U./ml) reduced the antiaggregating activity of PGI2 and PGD2. Heparin, when preincubated with platelet suspension, did not induce any significant change in the number/platelet (bs/plt) and affinity (Kd) of PGI2 and PGD2 binding sites (bs) in comparison to control values (PGI2 high affinity bs: bs/plt = 106 +/- 12 vs 107 +/- 17 - Kd = 9.7 +/- 3.1 vs 10.0 +/- 2.3 nM; PGI2 low affinity bs: bs/plt = 3551 +/- 233 vs 3670 +/- 465 - Kd = 877 +/- 125 +/- 125 vs 833 +/- 104 nM; PGD2 bs: bs/plt = 228 +/- 14 vs 234 +/- 24 - Kd = 68 +/- 10 vs 73 +/- 7 nM; p greater than 0.4 for all the differences). No significant binding modification was also observed when heparin was preincubated with 3H-PGI2 and 3H-PGD2. The present demonstration that heparin does not interfere with PGI2 and PGD2 binding to platelets is consistent with the hypothesis that heparin reduces the antiaggregating effects of PGI2 and PGD2 by directly potentiating platelet aggregation.