The Xbox 360 version has a glitch that allows you can automatically refill your endurance meter to full. When you have taken Endurance damage. Just go in Inventory, go to Armor, and re-equip your armor (highlight armor and press A), giving yourself a full endurance bar.
Complete the "Defeat Nasri's Guards" objective and stay in that room. Notice that there are three sets of stairs. There is a door behind two of them and another with a table across the top. In front of that table is a random ammo collectible. This collectible will respawn after around thirty seconds.