ObjectiveThe present study investigated the antagonism of the amino-terminal heptapeptide fragment of angiotensin II {[des-Phe8]-angiotensin II; Ang(1–7)} to angiotensin II (Ang II) both in vitro in rabbit aortae and in vivo in rats.Methods and resultsIn rabbit isolated endothelium intact aortic rings Ang(1–7) caused a concentration-related rightward displacement of the Ang II curve and depressed the maximum response to Ang II. By applying the data to a Schild plot an apparent pA2 of 5.5 was calculated. This depression of maximum response could be reversed by co-incubation of Ang(1–7) with the competitive angiotensin antagonist losartan. Ang(1–7) had no effect on the contractile responses of several other agonists. Intravenous infusion of 10 or 100 μg/kg per min Ang(1–7) had no effect on the resting blood pressure in the anaesthetized rat but inhibited Ang II-induced pressor responses.ConclusionThe present results show that Ang(1–7) is a specific non-competitive antagonist of Ang II at type 1 angiotensin II receptors.