Ratio between aldosterone and atrial natriuretic peptide in pregnancy

The possibility of evaluating the ratio between aldosterone and atrial natriuretic peptide (ANP) instead of the two hormones by themselves in studying sodium handling in normal pregnancy and in preeclampsia in the steady state and following albumin infusion was examined in this study. In 32 normal pregnancies monitored monthly, the highest aldosterone/ANP ratio was observed in the last weeks (28.7 +/- 12), and dropped in the first postpartum week (3.6 +/- 2.8), without changes in fractional excretion of sodium. In 18 preeclamptic patients, the ratio was significantly lower than in normal pregnancy at the same gestational ages, and it was coupled with absolute reduction in the sodium excretion. Among preeclamptic patients, a significant inverse correlation (P less than 0.025) was revealed between the ratio and sodium excretion. Natriuresis in response to acute volume expansion with albumin infusion occurred only in 50% of preeclamptic patients, and was associated with an ANP increase, an aldosterone decrease, and a further decrease in the ratio. A blunted natriuresis was observed in cases with a particularly low prealbumin value of this ratio. Furthermore, in preeclampsia, a particularly low ratio seemed to be typical of the patients who showed poorer placental flows and fetal outcomes. These results suggest that the balance between aldosterone and ANP may be a useful index in understanding sodium homeostasis in these settings.