Relationship of megakaryocyte ploidy with platelet number and size in cats, dogs, rabbits and mice

Feline platelets are larger than platelets of many other species. The following parameters were examined in 13 normal cats in an attempt to determine a reason for the difference: platelet count, mean platelet volume (MPV), platelet mass and ploidy of mature megakaryocytes. Average ± SEM platelet count was 213 000 ± 15000/μl, MPV was 11.1 ± 0.2 fl, and platelet mass was 2.4 ± 0.2 × 106 fl/μl. The predominant ploidy classes of feline megakaryocytes were 32N (41.6%) and 64N (47.1%). These findings were compared to existing data from normal dogs, rabbits, and mice. These species exhibited progressively higher platelet counts (313 000 ± 28 000, 568 000 ±35000, and 1328 000 ± 79 000/μl, respectively) and progressively smaller MPVs (7.2 ± 0.2, 4.4 ± 0.1 and 3.9 ± 0.1 fl, respectively) than cats. Platelet mass was the same in cats, dogs and rabbits, but it was much higher in mice (5.2 ± 0.3 × 106 fl/μl) The modal megakaryocyte ploidy was 16N in mice and 32N in dogs and rabbits. The MPV was directly related to the ploidy of fully mature megakaryocytes except when comparing dogs and rabbits for which MPVs differed, but ploidy distributions did not. The findings suggested that ploidy of a megakaryocyte may be one of the determinants of the size and number of platelets it will produce during normal haemopoiesis.