The Effect of Vincristine on the Platelet Count in Rats

Abstract

Summary. The effect of vincristine on the platelet count of rats is described. It was found that, depending upon dosage, the drug can cause either a thrombocytosis or marrow hypoplasia with thrombocytopenia in normal rats. Thrombocytosis was found even after prolonged treatment with vincristine when this was given at appropriate dosage. The thrombocytosis promoting effect of the drug was not enhanced by an increase in the splenic platelet pool or decreased by splenectomy. However, it was abolished when prior treatment was given to suppress marrow thrombopoiesis.

The effects of colcemid on hematopoiesis in the mouse.

“…The biphasic dose response and the timecouirse of these changes are also similar to those observed with Colcemid (25). The most pronounced thrombocytosis is observed with doses close to the minimutm dose requiired to prodtuce an effect (19)(20)(21)(22)(23)(24)(25). However, at higher dosage an early thrombocytopenia is followed by a late reactive thrombopoietic response.…”

“…In laboratory animals the transition from maximum thrombocytosis to thrombocytopenia is observed over a twofold range of vincristine dosage (19)(20)(21)(22)(23)(24)(25)(26)(27)(28). In contrast, in the present study thrombocytopenia was not observed over a sevenfold increase in Colcemid dosage.…”

“…Colchicine and its derivatives are known to induce endoreduplication and polyploidy in a variety of plant and animal cell systems (7)(8)(9)(10). Detailed studies in colchicine treated cell populations have shown that newly formed tetraploid cells are derived from cells that had previously been arrested in metaphase (7,8 (19)(20)(21)(22)(23)(24)(25) which has been attribuited to increased platelet produLction (19,20,22,23), secondary to an increase in marrow megakaryocytes (24), and megakaryocyte endomitosis (20). The biphasic dose response and the timecouirse of these changes are also similar to those observed with Colcemid (25).…”

“…Vincristine and vinblastine have since been shown to have a therapeutic effect in thrombocytopenias of varying etiologies (13)(14)(15)(16). Although immunosuppression (14,17) and alterations in platelet release (18) have been suggested as possible underlying mechanisms, laboratory investigations have suggested that the thrombocytosis was secondary to an increase in marrow production, resulting from an increase in number, size, and ploidy of megakaryocytes (19)(20)(21)(22)(23)(24)(25).…”

Reversible Thrombocytosis and Anemia Due to Miconazole Therapy

“…This reaction to miconazole administration may be similar to that described after the administration of vinca alkaloids in experimental animals or in humans (4,(6)(7)(8)10). It is possible that the impressive increase of peripheral platelets was related to mobilization of splenic thrombocytes, but such a mechanism remains speculative.…”