To assess the importance for vasoconstriction of in situ angiotensin (Ang)
II generation, as opposed to Ang II delivery via the circulation, we
determined forearm vasoconstriction in response to Ang I (0.1 to 10 ng.
kg(-1). min(-1)) and Ang II (0.1 to 5 ng. kg(-1). min(-1)) in 14
normotensive male volunteers (age 18 to 67 years). Changes in forearm
blood flow (FBF) were registered with venous occlusion plethysmography.
Arterial and venous blood samples were collected under steady-state
conditions to quantify forearm fractional Ang I-to-II conversion. Ang I
and II exerted the same maximal effect (mean+/-SEM 71+/-4% and 75+/-4%
decrease in FBF, respectively), with similar potencies (mean EC(50)
[range] 5.6 [0.30 to 12.0] nmol/L for Ang I and 3.6 [0.37 to 7.1] nmol/L
for Ang II). Forearm fractional Ang I-to-II conversion was 36% (range 18%
to 57%). The angiotensin-converting enzyme (ACE) inhibitor enalaprilat (80
ng. kg(-1). min(-1)) inhibited the contra