Plasma angiotensin II and blood pressure changes during dietary sodium manipulation

The renin-angiotensin system and dietary sodium have been repeatedly implicated in the pathogenesis of pregnancy induced hypertension (PIH). Mechanisms responsible for increased vascular responsiveness to angiotensin II (A-II) observed in PIH are not completely understood. Plasma A-II levels and blood pressure are functions of sodium balance in the non-pregnant state, but less is known about their relationship during gestation. Plasma levels of A-II increase in normal pregnancy, but the reported levels of this pressor substance circulating in subjects with PIH are in conflict. The pregnant rabbit demonstrates several conditions similar to those found in pregnant human subjects. We used this model to study the effects of dietary sodium manipulation on plasma levels of A-II and mean arterial pressure during late pregnancy in 30 chronically prepared New Zealand white rabbits. The animals were 24 to 28 days gestation (term 30 +/- 1 day). All animals were maintained on 1 of 3 diets for 8 days prior to operation and for the duration of the investigation: 10 were fed Purina regular chow (0.4% sodium), and permitted to drink 0.9% saline, 10 were fed trace-sodium diet (Purina 5881-R) and deionized water ad libitum; and 10 were continued on tap water and regular rabbit chow (0.4% sodium) and served as controls. Urines were collected for 24 hours prior to surgery for sodium determination. An indwelling catheter was placed in the carotid artery for blood pressure recording and blood sampling. After a 20 minute stabilization period, mean arterial pressure was repeatedly recorded and blood samples were obtained for determination of A-II levels and sodium concentration.(ABSTRACT TRUNCATED AT 250 WORDS)