PLATELET ALPHA-GRANULES CONTAIN A GROWTH-FACTOR FOR FIBROBLASTS

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  • 1 January 1979
    • journal article
    • research article
    • Vol. 53  (6) , 1043-1052
Abstract
Platelets contain a polypeptide growth factor that stimulates the replication of normal connective tissue cells. This platelet-derived growth factor (PDGF) is released during the clotting process. Human platelets from normal volunteers were disrupted by nitrogen cavitation, and the subcellular organelles were fractionated by ultracentrifugation through a 30%-60% sucrose gradient. EM revealed that fraction 7 (density 1.23 g/l) contained the largest number of .alpha. granules. The specific activity of platelet fibrinogen, an .alpha.-granule marker, was also highest in this fraction. The subcellular fractions were assayed for the presence of PDGF and for .beta.-thromboglobulin. PDGF was assayed quantitatively by the stimulation of DNA synthesis in confluent growth-arrested BALB/c[mouse fibroblast]-3T3 cells; the concentration of .beta.-thromboglobulin was determined by radioimmunoassay. The highest concentrations of PDGF and .beta.-thromboglobulin were in the .alpha.-granule fraction. .beta.-Glucuronidase, a lysosomal enzyme, was more diffusely distributed and had its highest specific activity in fractions of lower density than those for PDGF, .beta.-thromboglobulin or fibrinogen. The .alpha. granules of platelets provide a unique delivery system for PDGF, a polypeptide hormone with growth-promoting activity for connective tissue cells.