Decrease of angiotensin sensitivity after bed rest and strongly sodium-restricted diet in pregnancy.

Angiotensin II (A-II) sensitivity was determined in 23 nonmedicated nulliparas in the third trimester of pregnancy, before and after a 7- to 10-day period of bed rest and a strongly sodium-restricted diet (maximal 20 mmol Na+/24 hr). Seventeen nulliparous women had pregnancy-induced hypertension (PIH). The effective pressor dose (EPD), that is the minimal amount of A-II necessary for a 20 mm Hg elevation of the diastolic blood pressure, rose from a mean of 11.0 +/- 5.0 to 17.9 +/- 5.7 ng/kg/min. This is an increase of the mean of 63%. Six women were normotensive during the course of the pregnancy. They showed an increase of EPD from 12.6 +/- 4.9 to 28.3 +/- 10.9 ng/kg/min after sodium restriction and bed rest. This is a mean increase of 124%. It is concluded from this study that sodium not only is important in volume regulation but also seems to play a role in vessel wall reactivity. This effect of sodium on vascular reactivity could be the explanation for the favorable effect of a strongly sodium-restricted diet in lowering the incidence of eclampsia in women with PIH.