The Biology of Prostaglandins and Related Eicosanoids in Invertebrates: Cellular, Organismal and Ecological Actions

SYNOPSIS. Prostaglandins and related eicosanoids are oxygenatedmetabolites of C20 polyunsaturated fatty acids. These compoundshave been detected in species representing all major animalphyla. The significance of eicosanoids lies in two broad areasof animal biology. In one, eicosanoids are involved in regulationof many cellular events. In the other, eicosanoids facilitatecertain ecological interactions. Eicosanoids are known bestin the narrow context of their clinical signif-icance in humanmedicine. In this essay we suggest a new, broader paradigm forunderstanding the meaning of eicosanoids. Under this paradigm,called the biological paradigm, we note eicosanoids were recruitedinto roles as biological signal moieties long before the originsof the Metazoa. During the ensuing evolutionary diversificationof animals, eicosanoids have been used in a vast diversity ofbiolog ical roles, some of which occur only in invertebrates.We think this diversity endows eicosanoids with unusual explanatorypower in apprehending biological phenomena. In this review,we recount the literature on eicosanoids in protozoans and procaryotes,then provide a detailed review of the roles of eicosanoids ininverte-brate immunity. We draw upon recent work in parasitoiogyto outline an ecological role of eicosanoids in host-parasiterelationships. It appears to us that eicosanoids exert profoundeffects at the cellular, organismal and ecological levels ofbiologicalorganization. We suggest that continued inquiry into the biologicalsignificance of eicosanoids will yield important new informationon invertebrates.