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 Malpighian tubules isolated from adult ants, Formica polyctena, reduced basal fluid secretion rates. Inhibition of total eicosanoid biosynthesis with 100 μM 5,8,11,14-eicosatetraynoic acid (ETYA) and inhibition of prostaglandin biosynthesis with 100 μM indomethacin strongly reduced basal fluid secretion. The lipoxygenase inhibitor esculetin and the epoxygenase inhibitor SKF-525A did not influence fluid secretion rates during its application, although it blunted the cAMP effect somewhat after washout. These findings indicate that prostaglandins are involved in regulating fluid secretion rates in ant Malpighian tubules. Although stimulation by cAMP was somewhat reduced, the influence of ETYA and indomethacin on fluid secretion rates did not prevent adenosine 3′,5′-cyclic monophosphate from exerting its secretagogue effect. This indicates that the eicosanoid biosynthesis inhibitors acted in a physiological way on the Malpighian tubules. The eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid, is present in phospholipids of Malpighian tubules. This finding indicates that substrate for prostaglandin biosynthesis is available.