Effects of endotoxin treatment on the differentiation of guinea pig megakaryocytes to blood platelets.

The effect of endotoxin treatment (30 micrograms/kg body weight) on megakaryocyte development and platelet production in guinea pigs was investigated. A moderate thrombocytopenia was noted at 24 h after endotoxin administration. Recovery was observed at 48 h when the platelet count had almost reached the normal level. A significant increase in platelet production was obtained at 48 h, indicated by an enhancement in incorporation of labelled sulphate into platelets and also by an increase in the number of circulating heavier platelets. Megakaryocytes were classified into different developmental stages - megakaryoblast, promegakaryocyte, megakaryocyte - using standard morphological criteria (size, shape of nucleus, nucleus/cytoplasm ratio). The number of mature megakaryocytes increased at 24 and 48 h after endotoxin treatment. It was possible to distinguish between two different types of mature megakaryocytes - early mature and mature megakaryocytes - by the presence of a methanol-sensitive acid phosphatase. This enzyme is found mainly in mature, presumably platelet-forming, megakaryocytes and in platelets. The increased number of mature megakaryocytes at 24 h was due to an enhancement in the number of early mature megakaryocytes, whereas the change at 48 h was due largely to an increased number of mature, platelet-forming megakaryocytes. Megakaryocytes were isolated from bone marrow of guinea pigs by Percoll density-gradient centrifugation and incubated with radioactively labelled leucine. Compared with the untreated controls megakaryocytes isolated 24 h after endotoxin treatment took up and incorporated higher amounts of leucine into protein, indicating a higher metabolic capacity of the early mature megakaryocytes. No alteration in the ploidy distribution of megakaryocytes was noted after endotoxin treatment.