<prompt> Physiologically inactive form is:Angiotensin IAngiotensin IIAngiotensin IIIAngiotensin IV  <response>: Angiotensin I is 1 as potent as Ang II. Ang III and Ang II have qualitatively similar effects; both stimulate aldosterone secretion with equal potency, but Ang III is only 25 and 10 as potent as Ang II in elevating blood pressure and stimulating the adrenal medulla, respectively. Angiotensin III produces the hexapeptide sometimes called angiotensin IV, which is also said to have some activity.The lungs play an important role in activating angiotensin. The physiologically inactive decapeptide angiotensin I is converted to the pressor, aldosterone-stimulating octapeptide angiotensin II in the pulmonary circulation. Angiotensin III has about 40 of the pressor activity of angiotensin II, but 100 of the aldosterone-stimulating activity. Angiotensin III is simply a breakdown product with some biologic activity. The same is probably true of angiotensin IV, though some researchers have argued that it has unique effects in the brain.Structure of the amino terminal end of angiotensinogen and angiotensins I, II and III in humans. 