Synthesis of prostanoids and cyclic nucleotides by phagocytosing rat Kupffer cells

Abstract

Rat Kupffer cells in monolayer culture were allowed to phagocytose unopsonized zymosan granules. They responded with a strongly stimulated synthesis and release of prostanoids, mainly the immunologically determined prostaglandins PGE₂ and PGF_2α. The same response could be obtained by treatment with the calcium ionophore A23187. The effects of the ionophore and the zymosan particles were of the same magnitude but not additive. The rapid uptake of Ca²⁺ after contact with phagocytosable material recently described by us [(1983) Eur. J. Biochem. 131, 539–543] appears to mediate the enhanced prostaglandin synthesis. That response was suppressed not only by indomethacin but also by trifluoperazine which does not inhibit Ca²⁺ entry in the Kupffer cells. Similar effects by R24571 and 4-bromophenacyl bromide support the participation of calcium-calmodulin and of phospholipase A₂. The calcium channel blocker Verapamil® did not influence the zymosan-provoked production of prostaglandin PGE₂ nor were any indications obtained for a feedback inhibition by PGE₁ or PGE₂. Contact with zymosan resulted in a rapid but transient rise of the intracellular levels of cAMP and cGMP: 10 nM indomethacin completely blocked the increase of both cyclic nucleotides while trifluoperazine elicited different responses in the cAMP and cGMP levels. The stimulated release of prostaglandin E₂ was inhibited in a dose-dependent manner by nordihydroguaiaretic acid, an inhibitor of 5-lipoxygenase and by FPL 55712, known as a receptor antagonist for some leukotrienes. This suggests a regulatory role for its metabolites on prostaglandin synthesis.