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

SYNOPSIS. Prostaglandins and related eicosanoids are oxygenated metabolites of C20 polyunsaturated fatty acids. These compounds have been detected in species representing all major animal phyla. The significance of eicosanoids lies in two broad areas of animal biology. In one, eicosanoids are involved in regulation of many cellular events. In the other, eicosanoids facilitate certain ecological interactions. Eicosanoids are known best in the narrow context of their clinical signif-icance in human medicine. In this essay we suggest a new, broader paradigm for understanding the meaning of eicosanoids. Under this paradigm, called the biological paradigm, we note eicosanoids were recruited into roles as biological signal moieties long before the origins of the Metazoa. During the ensuing evolutionary diversification of animals, eicosanoids have been used in a vast diversity of biolog ical roles, some of which occur only in invertebrates. We think this diversity endows eicosanoids with unusual explanatory power 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 in inverte-brate immunity. We draw upon recent work in parasitoiogy to outline an ecological role of eicosanoids in host-parasite relationships. It appears to us that eicosanoids exert profound effects at the cellular, organismal and ecological levels ofbiological organization. We suggest that continued inquiry into the biological significance of eicosanoids will yield important new information on invertebrates.