Figure 37-2 Renin released into the circulation interacts with angiotensinogen to cleave off the decapeptide angiotensin I; through converting enzymatic activity, this becomes the active octapeptide angiotensin II. Angiotensin II is a potent vasopressor and has a direct effect on the adrenals to stimulate aldosterone. By its vasoconstrictive action, angiotensin II increases salt retention.