The regulation of prostaglandin and arachidonoyl-CoA formation from arachidonic acid in rabbit kidney medulla microsomes by palmitoyl-CoA

Abstract

Under physiological conditions, small amounts of free arachidonic acid (AA) are released from membrane phospholipids, and cyclooxygenase (COX) and acyl-CoA synthetase (ACS) competitively act on this fatty acid to form prostaglandins (PGs) and arachidonoyl-CoA (AA-CoA). In the present study, we investigated the effects of palmitic acid (PA) and palmitoyl-CoA (PA-CoA) on the PG and AA-CoA formation from high and low concentrations of AA (60 and 5 μM) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 μM [ 14C]-AA in 0.1 M-Tris/HCl buffer (pH 8.0) containing cofactors of COX (reduced glutathione and hydroquinone) and cofactors of ACS (ATP, MgCl 2 and CoA). After incubation, PG (as total PGs), AA-CoA and residual AA were separated by selective extraction using petroleum ether and ethyl acetate. PA (10–100 μM) had no effect on the PG and AA-CoA formation from either 60 or 5 μM AA. PA-CoA (10–100 μM) was without effect on the PG and AA-CoA formation from 60 μM AA, whereas it markedly decreased the PG formation (6–40%) and increased the AA-CoA formation (1.1–2.3-fold) from 5 μM AA, showing that the effects of PA-CoA on the PG and AA-CoA formation change depending on the AA concentration. These results suggest that PA-CoA, but not PA, may regulate the PG and AA-CoA formation at low substrate concentrations (close to the physiological concentration of AA), and that this in-vitro method using 5 μM AA may be useful for clarifying the homeostatic control of the metabolic fate of AA into these two enzymatic pathways.