RESUMEN
Erythropoietin (EPO) has been previously shown to affect platelet as well as red cell production. In addition, recent studies demonstrated that platelets from EPO-treated dogs are hyperreactive towards thrombin when compared to age-matched, control platelets. This report extends these observations by quantitating the thrombogenic potential of EPO in dogs. Dogs with arterio-venous (A-V) shunts received 100 U EPO/kg/day for 6 days, and thrombogenicity was serially monitored by insertion of a thrombotic surface into the A-V shunt. The resulting experimental thrombi were analyzed for platelet and erythrocyte content after formalin-fixation and chymotrypsin digestion, a technique which allows non-isotopic quantitation of cellular components. By day 5 of EPO-administration all animals demonstrated a significant increase in platelet and red cell content of the experimental thrombi; the average increase in platelet number was 2.94 +/- 0.12 fold (mean +/- 1 SE; n = 3; p = 0.006) above baseline while that for red cells was 2.46 +/- 0.18 fold above baseline (p = 0.023). After cessation of EPO, thrombogenicity returned to normal. During EPO-treatment, the percentage of thiazole orange-positive (TO+) platelets increased significantly to 17.2 +/- 1.6% (mean +/- 1 SE; n = 3) on day 5 compared to a pre-treatment level of 8.5 +/- 0.9% (p = 0.029). Although the percentage of TO+ erythrocytes also increased during the short course of EPO administration, the change was not significant. Despite the increases in TO+ cells, total platelet and erythrocyte counts did not change significantly within the time frame of these experiments. Fibrin/fibrinogen content of the experimental thrombi was unaltered with EPO-treatment. These data demonstrate that human EPO is pro-thrombotic in dogs and, in conjunction with earlier studies, suggest that hyperreactive platelets may be responsible for the potentiated thrombogenicity.
Asunto(s)
Plaquetas/fisiología , Eritropoyetina/farmacología , Trombosis/fisiopatología , Animales , Derivación Arteriovenosa Quirúrgica , Plaquetas/efectos de los fármacos , Perros , Recuento de Eritrocitos , Fibrina/análisis , Fibrinógeno/análisis , Humanos , Recuento de Plaquetas , Proteínas Recombinantes/farmacología , Factores de TiempoRESUMEN
Administration of erythropoietin (EPO) to adult dogs resulted in a dramatic increase in the number of thiazole orange-positive (TO+) platelets, also referred to as reticulated platelets. Pre-treatment level of TO+ platelets was 6.2 +/- 0.5% (mean +/- 1 SE: n = 5); following day 5 of treatment with 500 U EPO/kg/day, the percentage of TO+ platelets peaked at 16.8 +/- 2.3% (n = 5; p <0.02). After cessation of the hormone, the number of TO+ platelets fell rapidly to below starting levels. Unexpectedly, there was a significant decline in total platelet count during EPO administration despite an increased level of TO+ platelets. To assess platelet reactivity, total platelets and TO+ platelets from EPO-treated dogs were analyzed for thrombin-responsiveness as quantitated by P-selectin expression on the cell surface; reactivity was expressed as a thrombin EC50, the thrombin concentration required to activate 50% of platelets. Both total and TO+ platelets were hyperreactive during EPO treatment when compared either to pre-treatment values or to control animals. Thrombin EC50 values for total and TO+ platelets on day 5 fell to 66.5 +/- 5.4% (mean +/- 1 SE; n = 5; p <0.02) and 62.2 +/- 8.7% (n = 5; p <0.025), respectively, of pre-treatment levels. These data indicate that EPO not only promotes the synthesis of increased numbers of TO+ platelets in the dog but that these newly produced platelets are hyperreactive when compared to TO+ platelets from control animals.