Characterization of the contractile effects of human recombinant nonpancreatic secretory phospholipase A2 (PLA2) and other PLA2s on guinea pig lung pleural strips.

Contractile activities of nPLA2, pPLA2 and hPLA2 were characterized on pleural strips of guinea pig lung. The rank order of potency for these PLA2s was nPLA2 > pPLA2 > hPLA2. The concentration-related contractions induced by nPLA2 (0.0002-0.67 micrograms/ml), pPLA2 (0.006-20 micrograms/ml) and hPLA2 (0.1-30 micrograms/ml) appear to be mediated primarily by the formation of cyclooxygenase products and to a lesser extent by 5-lipoxygenase products, as revealed by experiments using indomethacin and BW A4C. To further support a PLA2-related mechanism, the selectivity and inhibitory effects of two irreversible PLA2 inhibitors, parabromophenacyl bromide (pBPB) and manoalogue, were evaluated against the contractile responses induced by each PLA2. Various concentrations of manoalogue and pBPB were incubated with individual PLA2s for 24 hr before initiating experiments. Both agents suppressed each PLA2-induced contractile activity in a concentration-related manner. The inhibitory effects of pBPB were similar at the highest concentration, whereas manoalogue was more effective in blocking contractions induced by pPLA2 and hPLA2. Conversely, methylated manoalogue, an inactive analog, failed to reduce the PLA2-induced contractions. These results demonstrate that hPLA2 has the ability to catalytically induce the release of arachidonic acid and the formation of proinflammatory eicosanoids that contract the pleural strips. This tissue bath preparation may be a useful model for the evaluation of novel PLA2 inhibitors as potentially useful therapeutic agents.