Platelet-derived mitogenic activity and bone marrow fibrosis in myeloproliferative disorders.

Mitogenic activity, measured as 3H-thymidine incorporation by NIH 3T3 cells, following stimulation with platelet-rich-plasma-derived serum (PRS), platelet-poor-plasma-derived serum and platelet extract was studied in 14 patients with myeloproliferative disorders (MPD) and 7 normal subjects. Reduced mitogenic activity was found in PRS and platelet extract of patients with MPD, as compared to controls. The average levels of platelet-derived growth factor (PDGF) equivalents were as follows: 16.3 +/- 7.2 pg/10(6) platelets in controls, 6.2 +/- 2.2 pg/10(6) (p less than 0.05) platelets in patients with polycythaemia vera, 1.8 +/- 0.4 pg/10(6) (p less than 0.01) platelets in patients with idiopathic myelofibrosis and 4.0 +/- 0.8 pg/10(6) (p less than 0.05) platelets in patients with essential thrombocythaemia (Dunnett test). A reduction of intraplatelet levels of beta-thromboglobulin, although not statistically significant, was found in the same patients. No apparent relation was found between the amount of PDGF equivalents and the degree of bone marrow fibrosis.