• Embryo development;
  • platelet-activating factor;
  • maternal recognition of pregnancy

ABSTRACT: Published reports of pregnancy associated thrombocytopenia in mice have utilized the Quackenbush strain. The inability of some laboratories to verify this observation in other mouse strains prompted us to report our findings by using Swiss Albino ICR mice. In Exp. 1, pregnant and pseudopregnant mice were bled prior to mating (time 0) and daily on day 1 (vaginal plug) through day 7. In Exp. 2, media from 24 hr cultures of 2-cell mouse embryos or media from unfertilized oocytes were injected into splenectomized mice. Animals were bled at time 0 (before injection) and at 30,60, and 120 min after injection. In Exp. 3, splenectomized mice were treated with either media from 2-cell stage embryos or with media supplemented with synthetic platelet-activating factor (PAF: 0.05, 0.1 or 0.2 μg). Animals were bled as in Exp. 2. Platelet numbers were determined in duplicate from each blood sample by using a hemacytometer. In Exp. 4, antagonist (SRI 63–441) or vehicle was administered to mated mice on days 1 through 4 of pregnancy. Animals were examined on day 8 to determine number of developing conceptuses. In Exp. 1–3, data were analyzed by using ANOVA for repeated measures, and in Exp. 4 data were analyzed by chi-square analysis. In Exp. 1, there was a treatment × time interaction (P<.06) due to transient thrombocytopenia in pregnant but not pseudopregnant mice. In Exp. 2, there was a significant treatment × time interaction (P<.02) with platelet numbers being markedly reduced at 30 min in animals treated with media from 2-cell embryos but not with media from unfertilized oocytes. In Exp. 3, the response to PAF was not different (P>.10) than the response to 2-cell embryo culture media. In Exp. 4, a total dose of 20 μg of antagonist did not alter (P>.1) the frequency of animals pregnant on day 8 while 20 μg/day of antagonist significantly (P<.05) reduced the frequency of animals that were pregnant. These data agree with reports using Quackenbush mice and support the hypothesis that reduction in platelet numbers is associated with early pregnancy in mice.