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Megakaryocytopoiesis and platelet production are stimulated during late
pregnancy and early postpartum in the rat
CW Jackson, SA Steward, RA Ashmun and TP McDonald
Department of Hematology/Oncology, St Jude Children's Research Hospital,
Memphis, TN 38101.
Platelet count during uncomplicated pregnancy shows considerable patient
variation. To gain a better understanding of thrombocytopoiesis during
pregnancy, megakaryocytes and platelets were examined during gestation and
the early postpartum period, using as a model the rat. Platelet counts and
megakaryocyte concentrations and DNA content distributions of
timed-pregnant rats were examined at intervals from day 10 of gestation
through parturition on day 22 and days 1 through 7 postpartum. Platelet
survival was studied in late gestation and the early postpartum. Platelet
volume was measured on gestation day 21. Platelet counts were moderately
increased on gestation days 17 and 19 through 22, and on days 2 to 3
postpartum. However, the actual rate of platelet production was much higher
than the platelet count suggests because the blood volume increased in late
gestation to 1.5 times the nonpregnant level. Mean platelet volume and
platelet volume distribution width of day 21 gestation rats were not
significantly altered. Platelet survival in pregnant rats was not
significantly different from that in nonpregnant females. In contrast,
megakaryocyte concentration was significantly increased on gestation days
12, 17, and 19 through 21, and 2 to 3 days postpartum. In addition, in late
gestation, megakaryocyte DNA content distributions displayed a marked
increase in the proportion of high ploidy cells, which peaked 1 day before
parturition. At that time, the proportions of 32N (43%) and 64N cells (3%)
were, respectively, three and four times nonpregnant values. In contrast to
megakaryocyte concentration, megakaryocyte DNA content distributions had
returned to the nonpregnant pattern by day 1 postpartum. The changes in
megakaryocyte DNA content distribution were accompanied by changes in
megakaryocyte size. These data indicate that thrombopoiesis is
substantially increased during late pregnancy, and that this increase is
accomplished through an increase in megakaryocyte DNA content and size, as
well as megakaryocyte number. The more rapid return of megakaryocyte DNA
content than of megakaryocyte concentration to nonpregnant levels
postpartum suggests that pregnancy-associated hormonal changes which
produce an increase in megakaryocyte DNA content and size differ from those
which cause an increase in megakaryocyte number.
Volume 79,
Issue 7,
pp. 1672-1678,
04/01/1992
Copyright © 1992 by The American Society of Hematology
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