IN-VITRO PRODUCTION OF ECDYSTEROIDS BY Y-ORGANS OF PENAEUS-VANNAMEI (CRUSTACEA, DECAPODA) - CORRELATION WITH HEMOLYMPH TITERS

Ecdysteroids secreted in vitro by Y-organs of the white shrimp Penaeus vannamei were quantified at different stages of the molt cycle by enzyme immunoassay (EIA). The production was maximal during the first hour of incubation, and the highest values were obtained with Y-organs from animals at molt stages D-1''' and D-2-D-3. Ecdysteroid production increased in parallel with the rise in hemolymph ecdysteroid levels, which peaked at the late premolt stage D-1'''. A preliminary characterization showed that 20-hydroxyecdysone was the major circulating ecdysteroid. Ecdysteroids present in the incubation median of Y-organs were measured after HPLC separation. Three major immunoreactive compounds comigrated with standard ecdysteroids, 20-hydroxyecdysone, ecdysone and 5-dehydroecdysone; a fourth, less polar immunoreactive product was also detected. 3-Dehydroecdysone appeared to be the predominant secretory product, and the other compounds could arise from its metabolism by contaminating epidermis cells in the Y-organ preparations.