Increase of the pressor response to angiotensin II in normal pregnancy. A sign of increasing blood volume more than decreasing vascular reactivity

: Plasma volume and the pressor dose of angiotensin II were estimated in 15 normotensive pregnant women during the second and third trimester and 2-3 months post-partum together. Plasma volume estimated by the Evans Blue technique increased during pregnancy significantly more than the body weight: its increase was 37 and 54% of the post-partum values whereas the body weight increase was only 6 and 12%. The pressor dose of angiotensin II was significantly increased during pregnancy only when it was related to body weight (14.2 +/- 4.3 and 14.9 +/- 5.2 at the 2nd and 3rd trimester versus 11.2 +/- 2.9 ng min-1 kg-1 BW post-partum) but not when it was related to plasma volume (0.25 +/- 07 and 0.26 +/- 0.09 versus 0.25 +/- 0.07 ng min-1 ml-1 PV). It is concluded that the increased pressor dose of angiotensin II (related to body weight) observed in normal pregnancy cannot be interpreted as an evidence for decreased vascular reactivity but that it could be a mere reflection of plasma volume increase.