Para-bromophenacyl bromide inhibits endothelium-dependent arterial relaxation and cyclic GMP accumulation by effects produced exclusively in the smooth muscle

Abstract

The alkylating agent para-bromophenacyl bromide (PBPB) has been reported to block endothelium-dependent relaxation of arteries, presumably by inhibiting phospholipase in the endothelium. We have investigated the site of action of PBPB-induced inhibition of melittin (MEL)- and bradykinin (BK)-stimulated endothelium-dependent relaxation and vascular smooth muscle (VSM) cyclic GMP (cGMP) accumulation. Studies were performed using short-term co-cultures of bovine pulmonary artery endothelial cells (EC) grown on microcarrier beads and rat aortic VSM. The culture system allowed separate pretreatment of ECs and VSM cells with PBPB (3 X 10(-5) M) before placement of the two cell types in co-culture. Because PBPB is an alkylating agent, it was felt that any blockade would endure after washout. Intracellular (VSM) concentrations of cGMP rose in response to MEL or BK stimulation only when EC were present, and were not decreased when only the EC had been pretreated with PBPB. cGMP accumulation induced by MEL or BK was significantly (P less than .01) inhibited in co-cultures where either the VSM alone or VSM and EC combined were pretreated with PBPB. The PBPB pretreatment adequately blocked EC phospholipase activity as measured by attenuation of the release of [3H]arachidonate from prelabeled EC by MEL. In parallel studies, when endothelium-derived relaxing factor was transferred by superfusion of EC to denuded rabbit aortic rings contracted with phenylephrine and pretreated with PBPB, the relaxation response induced by MEL or BK was inhibited. Similarly, when endothelium-derived relaxing factor was transferred to wells of cultured VSM pretreated with PBPB, cGMP accumulation was inhibited.(ABSTRACT TRUNCATED AT 250 WORDS)