Fall in blood pressure in response to volume expansion in pregnancy-associated hypertension (pre-eclampsia): why does it occur?

The infusion of 500 ml of a volume expanding solution caused a significant fall in blood pressure for up to 72 h in 35 women with pregnancy-associated hypertension of varying grades of severity. The response to the infusion was not obviously related to the clinical severity of the underlying disorder, nor to the extent of plasma volume expansion produced. The plasma volume of oedematous women increased, while there was no significant change in non-oedematous women in response to the infusion. Changes in other measurements were similar in oedematous and non-oedematous women. There was no evidence for prostacyclin release into the circulation in response to the infusion as a mediator of the blood pressure response. Both 6-keto-prostaglandin F1 alpha levels and 13,14-dihydro-15-keto-prostaglandin F (PGFM) levels fell significantly, suggesting suppression of prostaglandin release by the infusion. The antihypertensive effect of volume expanders in pregnancy-associated hypertension is mediated by a factor other than simple volume expansion.