THE EFFECT OF VOLUME EXPANSION ON PLACENTAL BLOOD-FLOW IN AWAKE HYPOVOLEMIC RATS IN LATE PREGNANCY

Symptomatic hypovolemia in preeclampsia is often treated by volume expansion. However, the effect of this treatment on placental blood flow is unclear. In the present study the hypothesis was tested that slow volume expansion, imposed on volume-depleted rats, does not compromise placental blood flow. Mild hypovolemia was induced in rats in late pregnancy by 24 hours' thirsting. The resulting gradual dehydration was associated with a 7% reduction in blood volume. These rats were then subjected to blood volume expansion by a continuous infusion with a plasma substitute. Volume expansion increased blood volume by 32% and cardiac output by 73%. The extra cardiac output was distributed to kidneys, carcass, and portal bed. Placental blood flow decreased by 31%. The pattern of response was comparable to the one previously observed in normovolemic rats. However, the magnitude of the changes was larger, probably associated with a delayed or impaired diuretic response. These data suggest that volume expansion therapy in midly hypovolemic pregnant rats elicits an exaggerated hemodynamic response as compared with normovolemic rats, including placental compromise.