Effect of pancreatic type phospholipase A2 on isolated porcine cerebral arteries via its specific binding sites

Abstract

The addition of porcine pancreatic group I phospholipase A₂ (PLA₂-I) produced a transient contraction followed by a relaxation in helical strips of porcine cerebral arteries. Its ED₁₀ value (2.3 nM) was almost identical to the K ₄ value(3.9 nM) calculated from the specific binding of ¹²⁵I-labeled porcine PLA₂-I in cultured porcine cerebral arterial smooth muscle cells. Type-specific action of PLA₂s and homologous desensitization strongly implicated the involvement of PLA₂-I-specific sites in the response. The transient contraction was abolished by treatment with indomethacin as well as by the removal of endothelium, indicating the dependence of vasoconstrictor prostoglandins synthesized by PLA₂-I in endothelium. The PLA₂-I-induced relaxation response was also observed in bovine and cat cerebral arteries, thus providing a new aspect of PLA₂-I as a vasoactive substance.