Hematologic changes and thrombopoietin production in mice after X-irradiation and platelet-specific antisera

Sera or plasma thrombopoietin (TSF) levels of mice were determined after: (a) no treatment; (b) induction of thrombocytopenia by injection of rabbit anti-mouse platelet serum (RAMPS); (c) exposure to 750 R or 900 R whole-body x-irradiation; or (d) irradiation and injection with RAMPS. Levels of TSF were assayed in thrombocythemic mice, using Na235SO4 uptake. RAMPS produced an immediate, severe thrombocytopenia without altering RBC or WBC counts of mice. Plasma collected from mice 4 hours after RAMPS injection increased both 35S incorporation into platelets (170% of control, P less than 0.005) and platelet counts (P less than 0.025) of TSF-assay mice. Although severe thrombocytopenia persisted, plasma TSF levels decreased thereafter, i.e., 111% of control after 8 hours and 99% of control after 16 hours. Platelet counts in mice exposed to 750 R and 900 R x-rays progressively decreased to severe thrombocytopenia by day 7, but almost normal RBC counts were maintained. Sera or plasma from animals with x-ray-induced thrombocytopenia caused significant increases in 35S incorporation into platelets of TSF-assay mice (196% of control, P less than 0.005 after 750 R and 141% of control, P less than 0.025 after 900 R). A combination of x-irradiation and RAMPS-injection did not produce greater TSF levels in mice than did x-ray or RAMPS treatment alone.