In vitro secretion of digestive phospholipase A(2) by midguts isolated from tobacco hornworms, Manduca sexta

We report on secretion of phospholipase A(2) (PLA(2)) by in vitro preparati ons of midguts isolated from tobacco hornworms, Manduca sexta. This enzyme is responsible for hydrolysis of fatty acids from the sn-2 position of phos pholipids, a necessary step in fatty acid absorption, The in vitro midgut p reparations are competent to secrete PLA(2) into incubation buffer, Secreti on began within the first 30 min of incubation and increased to a maximum a t 8 h, We selected 2 h incubations because substantial loss of tissue integ rity was observed after 8 h incubations. Using 2 h incubations, we recorded increased secretion of digestive PLA(2) from midguts incubated in buffer a mended with diet or with yeast as a component of the diet, We also recorded small increases in secretion of PLA(2) from midguts incubated in buffer am ended with a specific phospholipid, phosphatidylcholine. Midguts incubated in buffer amended with increased concentrations of phospholipid did not yie ld higher levels of PLA(2) activity, Lepidopteran midguts can be divided in to three regions, and we recorded the highest secretion of PLA(2) from the middle region and lowest secretion from the anterior region. Because isolat ed midguts responded to food chemicals with increased secretion of digestiv e PLA(2), we suggest that secretion of digestive enzymes in tobacco hornwor ms is regulated by a prandial and/or paracrine mechanism, as suggested for digestive proteases in other insect species. Arch. Insect Biochem, Physiol, 42:179-187, 1999. (C) 1999 Wiley-Liss, Inc.