Saralasin is a partial agonist of angiotensin II receptors, though it is commonly mistaken as a competitive antagonist. Saralasin's distinction as a partial agonist is based on the fact that its therapeutic effect (i.e. reduced hypertension) is only observed in patients with high plasma angiotensin II levels, but in patients with low angiotensin II levels Saralasin causes hypertension. In other words, the effects of Saralasin on the angiotensin II receptor in the absence of angiotensin II is pharmacodynamically similar to angiotensin II itself thus it is a partial agonist, because if it was an antagonist it would not elicit an effect when bound to its receptor. Saralasin is an angiotensin II analogue, containing sarcosine-1 and alanine-8, hence the name (sarcosine, alanine, angiotensin).
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