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Evaluation of ploidy of mature canine megakaryocytes, using Feulgen staining and microspectrophotometry.

OBJECTIVE
To evaluate megakaryocyte size and ploidy, using Feulgen staining and microspectrophotometry, in adult dogs with normal platelet count.


ANIMALS
Group A contained 8 and group B contained 11 adult dogs.


PROCEDURE
Megakaryocytes were evaluated by light microscopy and staged according to maturation status. Stage-III megakaryocytes were measured and mapped for future relocation. Bone marrow aspirates were destained and restained, using the Feulgen method. Previously identified stage-III megakaryocytes were measured for DNA content, using microspectrophotometry.


RESULTS
Megakaryocyte size correlated with ploidy values, and mean sizes within ploidy groups were significantly (P < 0.05) different from each other for both groups. The model ploidy value of stage-III megakaryocytes, which represented 18% of the total megakaryocyte population of the combined groups, was 32N. This is in contrast to results of flow cytometric studies, which indicated that the modal ploidy value for all canine megakaryocytes was 16N.


CONCLUSIONS
Reasons for the disparate results between microspectrophotometric techniques and flow cytometry include maturation stage of the megakaryocyte population evaluated and percentage of megakaryocytes within that maturation stage. Flow cytometric methods, which evaluate all megakaryocytes detectable by antibody, may include cells still capable of DNA synthesis, resulting in a shift in the observed modal ploidy value. Recognition of the difference between canine and human megakaryocyte ploidy distribution is important, particularly in studies in which the dog is used as an animal model for human megakaryocytopoiesis.