Characterization of prostanoid receptors on rat neutrophils

1 The effects of various prostanoid agonists have been compared on the increase in intracellular free calcium ([Ca 2+ ] i ) and the aggregation reaction of rat peritoneal neutrophils induced by N‐formyl‐L‐methionyl‐L‐leucyl‐L‐phenylalanine (FMLP). 2 Prostaglandin E 2 (PGE 2 ) and the specific IP‐receptor agonist, cicaprost, both inhibited the FMLP‐induced increase in [Ca 2+ ] i (IC 50 33 n m and 18 n m respectively) and the FMLP‐induced aggregation reaction (IC 50 5.6 n m and 7.9 n m respectively). PGD 2 , PGF2 α , and the TP‐receptor agonist, U 46619, were inactive at the highest concentration tested (1 μ m ). 3 The EP 1 receptor agonist, 17‐phenyl‐ω‐trinor PGE 2 , and the EP 3 ‐receptor agonists, GR 63799X and sulprostone, had no inhibitory effect on FMLP‐stimulated rat neutrophils. 4 PGE 1 (EP/IP‐receptor agonist) and iloprost (IP‐receptor agonist) inhibited the FMLP‐induced increase in [Ca 2+ ] i with IC 50 values of 34 n m and 38 n m respectively. The EP 2 ‐receptor agonists, butaprost and misoprostol (1 μ m ), inhibited both FMLP‐stimulated [Ca 2+ ] i and aggregation. However another EP 2 ‐receptor agonist, AH 13205, was inactive in both assays. 5 Prostanoid receptors present on rat neutrophils were further characterized by measuring [ 3 H]‐adenosine 3′:5′‐cyclic monophosphate ([ 3 H]‐cyclic AMP) accumulation. Only those agonists capable of stimulating [ 3 H]‐cyclic AMP accumulation were able to inhibit both FMLP‐stimulated [Ca 2+ ] i and aggregation. 6 These results indicate that rat neutrophils possess inhibitory IP and EP‐receptors; the relative potencies of PGE 2 , misoprostol and butaprost are those expected for the EP 2 ‐receptor subtype. No evidence for DP, FP, TP or EP 1 and EP 3 ‐receptors was obtained.