Increased red cell aggregation does not reduce uteroplacental blood flow in the awake, hemoconcentrated, late-pregnant guinea pig.

The effect of increased red blood cell aggregation on uteroplacental blood flow was studied in 11 awake, late-pregnant guinea pigs. The aggregation of the red cells was increased by administering high molecular weight dextran (HMWD) to the previously hemoconcentrated animal. The purpose of the hemoconcentration before HMWD was 1) to use a preeclampsia model in which the hemorheology may be impaired because of the combined effect of polycythemia, an increased red cell aggregation, and an increased plasma viscosity and 2) to potentiate the aggregation-increasing effect of HMWD. Relative to the pre-HMWD condition, arterial blood pressure and systemic vascular resistance increased by 10 and 26%, respectively. The cardiac output fraction shunted across the systemic circulation and the arterial hematocrit decreased by 30 and 4%, respectively. Neither cardiac output nor the weighted organ flows, including those to the placentas, changed in response to the rise in red cell aggregation. We conclude that an imposed increase in red cell aggregation has no appreciable effect on uteroplacental blood flow in the awake and healthy late-pregnant guinea pig. These data do not exclude the possibility that increased red blood cell aggregation potentiates the negative effects on uteroplacental blood flow, e.g. in pregnancy-induced hypertension or preeclampsia, where the placenta is not only marginally perfused but also frequently damaged histologically.