Distinction between responsiveness of macrophages to cyclic-AMP elevation by prostaglandin E2 and prostacyclin

Macrophages, isolated from carrageenin-induced granuloma (an immune-related inflammatory model), were used to examine the effects of prostaglandin E2 and prostacyclin on intracellular levels of cyclic-AMP. It appears that during the development of the tissue-growth component of this granuloma in rats the infiltrating mononuclear phagocytes undergo a change, resulting in macrophages which are very sensitive to cyclic-AMP elevation by PGE2 but insensitive to a similar effect of prostacyclin. Arguments are presented that the difference between the responsiveness of these macrophages to PGE2 and prostacyclin observed in vitro is directly related to the previously reported distinction between these two metabolites of arachidonate as inhibitors of the carrageenin-induced granuloma in vivo.