Losartan is a non-peptide, orally active angiotensin II receptor antagonist. It works by blocking the action of angiotensin II, a potent vasoconstrictor, which ultimately leads to the relaxation of blood vessels and a reduction in blood pressure. As an angiotensin II receptor antagonist, Losartan specifically targets the AT1 receptor, preventing angiotensin II from binding to it. This action helps in managing hypertension and reduces the risk of stroke in patients with high blood pressure and an enlarged heart. Losartan is commonly prescribed for the treatment of hypertension and for the protection of kidneys in patients with type 2 diabetes. It is also used in cases of heart failure and to improve survival after a heart attack.

**_ Saralasin is a peptide analog of angiotensin II and acts as a partial agonist/antagonist at angiotensin receptors. Due to its peptide nature, it is not orally active and requires parenteral administration. Therefore, it does not fit the criteria of being a non-peptide, orally active angiotensin II receptor antagonist. Lisinopril is an angiotensin-converting enzyme (ACE) inhibitor, not an angiotensin II receptor antagonist. It works by inhibiting the conversion of angiotensin I to angiotensin II, thereby lowering blood pressure. However, it is not classified as an angiotensin II receptor antagonist. Similar to Lisinopril, Enalapril is also an ACE inhibitor. It prevents the formation of angiotensin II by inhibiting the enzyme ACE, which converts angiotensin I to angiotensin II. It is not an angiotensin II receptor antagonist. Among the given options, Losartan is the correct answer as it is a non-peptide, orally active angiotensin II receptor antagonist. It is effective in treating hypertension and related cardiovascular conditions by blocking the action of angiotensin II at the AT1 receptor.