Levels of Plasma Atrial Natriuretic Peptide and Plasma Renin Activity, and The Ratio between Them During Normal and Preeclamptic Pregnancies

To clarify the possible role of atrial natriuretic peptide (ANP) and plasma renin activity (PRA) in the pathophysiology of preeclampsia, and to evaluate the relationship between ANP and PRA in normal and preeclamptic pregnancies, we simultaneously measured ANP and PRA levels, and also determined ANP/PRA ratios in both normal pregnants (n=8) and preeclamptic patients (n=8) within their third trimesters. In the normal and preeclamptic pregnant women, mean (±SE) plasma ANP values were 25.48 ± 5.52 and 36.27 ± 6.70 pg/ml; and mean (±SE) PRA values were 2.70 ± 0.56 and 3.21 ± 1.09 ng/ml/h, respectively. The higher plasma ANP and PRA values in the preeclamptics were found to be non-significant. Mean (±SE) ANP/PRA ratio in the preeclamptic group was determined to be higher than that in normal pregnancy, the values being 23.0 ± 8.41 pg/ml and 14.05 ± 4.16 ng/ml/h respectively; this difference between the two groups was also found to be nonsignificant. Despite plasma volume reduction in preeclampsia, elevated plasma ANP levels suggest that ANP may be released in response to a rise in intra-atrial pressures secondary to hypertension in this state. It is also concluded that ANP, which is also a potent vasorelaxant, can induce compensatory mechanisms in preeclampsia following increased PRA levels, which otherwise would trigger release of angiotensin II and aldosterone further and hence cause vasoconstriction and sodium retention to be more augmented.