Effect of sodium chloride and sorbitol infusions on vascular angiotensin reactivity during third trimester pregnancy

Normal pregnancy is associated with refractoriness to the pressor effects of i.v. administered angiotensin II (A II). In pre-eclampsia, this refractoriness to A II is lost several weeks prior to the increase of blood pressure. Infusions of 200 ml of 3% saline or of 40% sorbitol over 30 min, or administration of 2,000 ml of normal saline infused over 2 h, respectively, resulted in an increased vascular angiotensin sensitivity. The effective angiotensin pressor dose (APD) decreased significantly after each test substance (decrease of the mean APD 14.5% after 3% saline, 24% after 40% sorbitol and 25% after normal saline). The data confirm the hypothesis that the principal determinant of pressor responsiveness to A II during pregnancy is arteriolar response; this seems to be modulated by alterations in the sodium content of the vessel wall.