EICOSANOID BIOSYNTHESIS INHIBITORS MODULATE BASAL FLUID SECRETION RATES IN THE MALPIGHIAN TUBULES OF THE ANT, FORMICA-POLYCTENA

Inhibition of eicosanoid biosynthesis in in vitro preparations of Malp ighian tubules isolated from adult ants, Formica polyctena, reduced ba sal fluid secretion rates. Inhibition of total eicosanoid biosynthesis with 100 mu M 5,8,11,14-eicosatetraynoic acid (ETYA) and inhibition o f prostaglandin biosynthesis with 100 mu M indomethacin strongly reduc ed basal fluid secretion. The lipoxygenase inhibitor esculetin and the epoxygenase inhibitor SKF-525A did not influence fluid secretion rate s during its application, although it blunted the cAMP effect somewhat after washout. These findings indicate that prostaglandins are involv ed in regulating fluid secretion rates in ant Malpighian tubules. Alth ough stimulation by cAMP was somewhat reduced, the influence of ETYA a nd indomethacin on fluid secretion rates did not prevent adenosine 3', 5'-cyclic monophosphate from exerting its secretagogue effect. This in dicates that the eicosanoid biosynthesis inhibitors acted in a physiol ogical way on the Malpighian tubules. The eicosanoid-precursor polyuns aturated fatty acid, arachidonic acid, is present in phospholipids of Malpighian tubules. This finding indicates that substrate for prostagl andin biosynthesis is available.