EFFECTS OF INHIBITOR OF ENDOTHELIUM-DERIVED RELAXING FACTOR ON HYPOXIC CONTRACTION OF ISOLATED PIG CORONARY-ARTERY

Exposure of isolated pig coronary artery with endothelium intact to hypoxia Krebs-Henseleit solution aerated with 95 % N-2 + 5 % CO2 caused a transient contractile response, and the coronary artery without endothelium exhibited a gradual decrease in basal tension. The endothelium-dependent contractile response to hypoxia was almost completely blocked by nitro-L-arginine (0.2 mmol . L(-1)), and inhibited by methylthioninium chloride (10 mu mol . L(-1)). The inhibitory effect of the NLA was partially reversed by L-arginine (2 mmol . L(-1)). Sodium nitroprusside (10 mu mol . L(-1)) was also completely antagonized and nicorandil (0.3 mol . L(-1)) remarkably reduced the hypoxic contractile; response. Tetraethylammonium (10 mmol . L(-1)) and glibenclamide (1 mu mol . L(-1)) had little effect on hypoxia-induced vascular constraction, whereas cromakalim (1 mu mol . L(-1)) produced obvious relaxing effect on hypoxic response. These results suggest that suppression of basally released nitric oxide (NO) is an important mechanism of coronary vasoconstriction induced by hypoxia.