Eicosanoid biosynthesis by hemocytes from the tobacco hornworm, Manduca sexta

We describe eicosanoid biosynthesis by microsomal-enriched preparations of hemocytes from larvae of the tobacco hornworm Manduca sexta. Four major prostaglandins, PGA2, PGE2, PGD2, and PGF2 alpha, and a lipoxygenase product that co-chromatographed with 15-hydroxyeicosatetraenoic acid (HETE) were synthesized under most conditions. The HETE's fraction was the predominant product. Eicosanoid biosynthesis was sensitive to experimental conditions, including incubation time, temperature, and protein concentration. Optimal biosynthesis was observed with 1.5 mg of microsomal-enriched protein, incubated at 30 degrees C for 2 min. The hemocyte preparation is sensitive to low dosages of naproxin and esculetin. As in mammals, most lipoxygenase activity (87%) was localized in the cytosolic fraction of hemocytes. Unlike mammals, in which PGH synthase is associated with intracellular membranes, the hemocytic activity was detected in microsomal (59%), cytosolic (35%) and mitochondrial fractions (5%).