Twelve women in their first 3 months of pregnancy received an i.v. saline load (3 mmol sodium/kg) and a graded infusion of angiotensin II (Ang II; i.e. 4, 8 and 16 ng/kg per min). As controls, twelve comparable pregnant subjects received the saline infusion alone. Eight non-pregnant women underwent both protocols, with doses of 2, 4 and 8 ng/kg per min Ang II, and thus acted as their own controls. Saline loading evoked proportionately similar falls in basal plasma renin (PRC) and plasma aldosterone (PAC) concentrations in pregnant and non-pregnant women. Angiotensin II evoked a dose-dependent pressor response, a graded increase in PAC and a reduction in sodium and urate excretion in both pregnant and non-pregnant women. The administration of Ang II had a proportionately greater effect on sodium and urate excretion in non-pregnant than in pregnant women; the pressor response to Ang II was also decreased in the pregnant women. The stimulation of PAC by Ang II, however, did not differ between the two groups. These results show that refractoriness to the renal and vascular effects of Ang II is present as early as the eleventh week of gestation. They also support the hypothesis that there is a degree of dissociation between the renin-angiotensin system and PAC in normal pregnancy.
