The effect of non-immune stresses on the development of Strongyloides ratti.

Strongyloides ratti is a parasitic nematode of rats. The host immune response against S. ratti affects the development of its free-living generation, favouring the development of free-living adult males and females at the expense of directly developing, infective 3rd-stage larvae. However, how the host immune response brings about these developmental effects is not clear. To begin to investigate this, we have determined the effect of non-immune stresses on the development of S. ratti. These non-immune stresses were subcurative doses of the anthelmintic drugs Ivermectin, Dithiazanine iodide and Thiabendazole, and infection of a non-natural host, the mouse. These treatments produced the opposite developmental outcome to that of the host immune response. Thus, in infections treated with subcurative doses of Ivermectin, Dithiazanine iodide and in infections of a non-natural host, the sex ratio of developing larvae became more female-biased and the proportion of female larvae that developed into free-living adult females decreased. This suggests that the mechanism by which the host immune response and these non-immune stresses affect S. ratti development differs.

Evidence for a selective and electroneutral K+/H(+)-exchange in Saccharomyces cerevisiae using plasma membrane vesicles.

The existence of a K+/H+ transport system in plasma membrane vesicles from Saccharomyces cerevisiae is demonstrated using fluorimetric monitoring of proton fluxes across vesicles (ACMA fluorescence quenching). Plasma membrane vesicles used for this study were obtained by a purification/reconstitution protocol based on differential and discontinuous sucrose gradient centrifugations followed by an octylglucoside dilution/gel filtration procedure. This method produces a high percentage of tightly-sealed inside-out plasma membrane vesicles. In these vesicles, the K+/H+ transport system, which is able to catalyse both K+ influx and efflux, is mainly driven by the K+ transmembrane gradient and can function even if the plasma membrane H(+)-ATPase is not active. Using the anionic oxonol VI and the cationic DISC2(5) probes, it was shown that a membrane potential is not created during K+ fluxes. Such a dye response argues for the presence of a K+/H+ exchange system in S. cerevisiae plasma membrane and established the non-electrogenic character of the transport. The maximal rate of exchange is obtained at pH 6.8. This reversible transport system presents a high selectivity for K+ among other monovalent cations and a higher affinity for the K+ influx into the vesicles (exit from cells). The possible role of this K+/H+ exchange system in regulation of internal potassium concentration in S. cerevisiae is discussed.

Development of a chemotherapeutic model for microfilaricidal drugs to Dirofilaria immitis.

Microfilariae obtained from in vitro culture of adult Dirofilaria immitis were inoculated into naive dogs and used to test the in vivo efficacy of the antimicrofilarial drug Dizan. Injection of 33 million microfilariae into a 3-month-old male beagle pup over a 5-day period resulted in a microfilaremia that peaked at 863 microfilariae per ml on day 30. Treatment with Dizan resulted in a rapid clearance of microfilariae from the peripheral circulation. Four additional male beagle pups that were each given a total of 31 million microfilariae over 100 days maintained an average of 25 microfilariae per ml for 2 months. Microfilaremias were monitored by ELISA, a modified Knott's method and selected blood chemistry tests. It was shown that after residing in the peripheral circulation the microfilariae were able to develop into infective larvae in mosquitoes; therefore, the system may be a reasonable model of the natural microfilaremic state.

Clinical laboratory evaluations of seven heartworm infected beagles: during disease development and following treatment.

Clinical laboratory evaluations were performed in 7 beagles for 12 months following experimental infection with Dirofilaria immitis and for 14 months following adulticide and microfilaricide treatment. Few abnormalities were detected. A mild basophilia and thrombocytopenia developed late during the year of infection and after arsenical treatment there were transient increases in eosinophils, SGPT, and SAP. Coagulation and blood gas studies were normal. The minimal changes were attributed to either: (1) the one year infection with 50 infective larvae was an insufficient insult or (2) an idiosyncrasy in the host-parasite relationship is required in order to produce marked alterations in clinical laboratory evaluations.

Detection of activity for various anthelmintics against in vitro-produced Cooperia punctata.

The in vitro-grown parasitic stages of Cooperia punctata were used to evaluate 28 compounds with different kinds and degrees of in vivo activity. Using presumptive and confirmatory tests, it was possible to establish a group order of in vitro potency that compared favorably with an order based on established in vivo use of these compounds. The procedure lends itself to evaluating activity against a given parasitic growth stage and gives a quantitative estimate (range) of the concentration that produces 50% nematode kill. The system was most successful in detecting compounds with in vivo activity for C punctata, followed in order by compounds active against Cooperia spp, other gastrointestinal nematodes of ruminants, and other nematodes of non-bovine hosts. The procedure showed some differentiation between activity against nematodes versus that against cestodes, trematodes, and arthropods. The system permits considerable flexibility in experimental design, thus making possible the acquisition of the particular information desired. In addition to establishing lethal effects on the nematode, the procedure detected compounds with nematode-anesthetizing effects. The results indicate this in vitro system can be used with some expediency as a preliminary screening method in the search for new anthelmintic compounds.