Prostaglandin synthetase activity in bovine adrenocortical cells and subcellular preparations: effect of ACTH.

Prostaglandin (PGE2, PGF2 alpha) production by bovine fasciculo-reticulata adrenocortical cell suspensions was examined using specific radioimmunoassay procedures. No detectable PGs (greater than 50 pg) could be measured in the extract from up to 2 x 10(6) cell incubations after 1 h, with or without the presence of ACTH, although these cells expressed full steroidogenic capabilities under these conditions. The same preparations could produce PGs when supplemented with arachidonic acid but ACTH had no effect on this process. These negative findings could not be explained by analytical artifacts or metabolic transformation. However, an active PG synthetase system was characterized in bovine adrenocortical subcellular preparations. This system converted arachidonate and endogenous substrate(s) to PGE2 as the major product. No thromboxane or prostacyclin pathways were detected even at high enzyme/substrate ratio. Although the microsomal adrenal cortex PG synthetase activity shares many features with those observed in other tissues (Km = 8.3 x 10(-5) M, optimal pH at 8.0, stimulation of PGE2 formation in the presence of glutathione and L-epinphrine), its specific activity was comparatively low (Vmax = 2.5 ng PGE2/min/mg microsomal proteins), which may explain our negative findings using cell suspensions. These findings do not provide evidence to support the hypothesis proposing a role of endogenous PGs in the mechanism of acute ACTH action in the case of bovine adrenal cortex.