Effects of vasodilation and constriction on blood vessel regression. (A-C) Effect of captopril on oxygen-induced vaso-obliteration. Nine-day-old pups were injected periocularly with 5 μL of vehicle (A) or 300 mg/mL captopril (B); 4 hours later, animals were placed into high oxygen chamber and retinas were analyzed after another 24 hours. (C) Quantification of avascular areas. Fellow untreated eyes were used as a control. Original magnifications, ×40. (D-E) Effect of ITV mock injection (D) or injection of 0.75 μL of 0.2M of angiotensin II (Ang II) (E) on retinal blood vessels. Collagen IV staining (red) and GS lectin staining (green). Original magnifications, ×200. (F-I) Effect of ITV mock injection (F) or injection of 0.25 μL of 20 mg/mL of adrenomedullin (G) on retinal blood vessels exposed to high oxygen for 6 hours (F-G) or 24 hours (H-I). GS lectin staining (green) and ConA perfusion (red). Original magnifications, ×40.