Inhibition by juvenile hormone of growth of Crithidia fasciculata in culture

Activity of juvenile hormone and juvenile hormone analogues on the growth of Trypanosoma cruzi

The effects of juvenile hormone-III (JH-III) and the juvenile hormone analogues (JHA) methoprene and fenoxycarb on the growth and macromolecular biosynthesis in Trypanosoma cruzi were studied in vitro. It was observed that JH-III and JHA blocked growth and 3H-thymidine incorporation without killing the cells within certain concentrations (< or = 1 x 10(-4) M), but they caused cellular death at concentrations over 1 x 10(-3) M. The inhibitory effect on growth was partially reversible. On the other hand, the inhibitory action of JH-III, methoprene and fenoxycarb was an unspecific effect according to the results obtained with Leishmania mexicana mexicana (promastigotes) and human peripheral blood lymphocytes. The JHA have a good possibility of being used in the control of trypanosomiasis.

Hormonal effects on insects and other endoparasites in vitro

Metamorphic and reproductive events in vertebrates and invertebrates are under endocrine control and are often correlated with developmental, behavioral, or reproductive changes in the parasites living in or on these hosts. This paper reviews selected examples of a) host hormone mediated influences on endoparasites in vivo, b) host hormone effects in vitro on protozoan, helminth, and insect endoparasites, and c) identifies possible relationships in hormone effects across parasite taxa. The significance of studies on endoparasites in vitro in relation to the impact of host hormones, antihelminthic, and prophylactic drugs on parasite growth and proliferation will also be addressed. A review of the literature indicates only limited studies have been done in vitro in an attempt to elucidate the bases of reported host hormone influences on endoparasites in vivo. Steroid hormones of hosts seem to stimulate growth, molting or encystment or both of helminth, insect, and protozoan parasites. Vertebrate steroids such as estrogen, testosterone, and progesterone had primarily reproduction- or growth-promoting effects or both on protozoan and nematode parasites. Insect ecdysteroids such as ecdysone, 20-hydroxyecdysone, and makisterone were the most widely studied steroids in vitro and induced growth or molting or both of cestode, nematode, and insect parasite larvae. Although juvenile hormone (JH III) stimulated growth in the protozoan and nematode parasites tested, the analogue methoprene and JH precursors, farnesal, farnesol, and farnesol methyl ether had various effects. Biogenic amines also varied in their effects on the nematode parasites tested, while the peptide hormone, insulin, stimulated growth in the protozoans tested. The evidence for in vitro effects of host hormones on their natural endoparasites is patchy at best. Additional studies are needed to identify the biochemical bases for the numerous host hormone mediated effects on parasites.