Physiologically inactive form is:
Correct Answer: Angiotensin I
Description: 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.
Category:
Physiology
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