Steroidal enhancement of growth in parasitic larvae of Ascaris suum: validation of a bioassay.

Third-stage larvae of the swine parasitic roundworm, Ascaris suum, were grown in stationary multiwell cultures in the presence of synthetic steroid hormones or the HPLC fractions of a steroid extract of adult female reproductive tracts to determine the subsequent effect of these compounds on length of 4th-stage larvae. Log doses of ecdysone, 20-hydroxyecdysone, progesterone, and makisterone standards, from 50 pg/ml to 500 ng/ml, were incubated with larvae for 1 day in RPMI-1640 supplemented with cholesterol. Length measurements were made on 4th-stage larvae after an additional 6 days of incubation. All compounds and extracts had a dose-dependent enhancement on length of these larvae; the partially purified extracts were more potent than their synthetic analogs. All standards and extracts except makisterone showed reduced or no response at higher dose levels. In contrast, makisterone continued to have maximal effect from 500 pg/ml to 500 ng/ml. Short exposure period to the steroid and low concentration were critical to demonstrate enhanced growth in this homologous bioassay.