Circadian rhythm of plasma atrial natriuretic peptide, aldosterone, and blood pressure during the third trimester in normal and preeclamptic pregnancies.

The influence of pregnancy on circadian variations of plasma atrial natriuretic peptide and aldosterone was studied. In those women with normal pregnancies, the mean 24-hour values of atrial natriuretic peptide and aldosterone increased, compared with the levels in normal nonpregnant subjects. In cases of severe preeclampsia, levels of atrial natriuretic peptide were significantly higher than in the other subjects, but aldosterone levels decreased to nearly those seen in the nonpregnant subjects. Atrial natriuretic peptide did not establish a rhythm in normal nonpregnant and pregnant subjects, but in the studies of aldosterone levels, a clear circadian rhythm was evident. In severe cases of preeclampsia, atrial natriuretic peptide established a circadian rhythm similar to that of blood pressure, and the circadian rhythm of aldosterone disappeared. The main characteristic of the rhythm in atrial natriuretic peptide and blood pressure in women showing preeclamptic signs is that the acrophase occurred at midnight. This evidence suggests that in women with symptoms of preeclampsia the load to the atria increases at midnight.