Histochemical Distribution of "Leucine" Aminopeptidase in Oesophagostomum radiatum Grown In vivo and In vitro

The distribution of nonspecific leucine aminopeptidase (LAP) in Oesophagostomum radiatum infective larvae, all phases and stages of parasitic development in cattle, and through the fourth stage in vitro was determined histochemically using fresh frozen sections and the substrate, L-leucylbeta-naphthylamide. LAP was not present in ensheathed and artificially exsheathed infective larvae. LAP was present and limited to the body wall layers, intestine, excretory gland cells, and parts of the reproductive system in parasitic larval stages and adults, and in mature male copulatory organs. Major sites of LAP were in the intestine of larvae and the intestine, developing sex cells and walls of some reproductive organs of adults. LAP-positive "lysosomelike bodies or granules" were detected intracellularly and extracellularly in the intestine and intracellularly in cells undergoing oogenesis, ova, somatic muscles, hypodermal chords, genital primordia, and immature adult testis and ovaries. There were no essential differences in the distribution and activity of LAP between histotropic larvae in situ and isolated larvae, between comparable stages grown in vivo or in vitro, and between comparable stages grown in different culture systems. The enzyme's presence in the nematode appears to be primarily involved with intestinal functions. There was no evidence of its involvement with the processing of molting and ecdysis.