APPARENT INHIBITION OF IN-VITRO JUVENILE-HORMONE BIOSYNTHESIS BY THE CORPUS CARDIACUM OF ADULT CRICKETS (GRYLLUS-BIMACULATUS AND ACHETA-DOMESTICUS) IS DUE TO JUVENILE-HORMONE ESTERASE

When measuring the in vitro JH III-biosynthesis by corpora allata (CA) from adult female crickets in the presence of corpora cardiaca (CC), the amount of JH III in the medium decreased in a dose dependent manne r. The CC of a 4-day-old female Gryllus bimaculatus contain 42 pmol.pa ir CC(-)1 Grb-AKH, 0.62 pmol.pair CC-1 octopamine, and a JH-esterase a ctivity of 9.8 pmol JH.h(-1).pair CC-1. Comparable values for Acheta d omesticus are 21 pmol.pair CC-1 Grb-AKH, 0.53 pmol.pair CC-1 octopamin e, and 6.5 pmolJH.h(-1).pair CC-1 of JH-esterase activity. Even if the entire octopamine content of the CC were released into the medium, th e concentration would be below the 10(-5) M threshold for octopamine i nhibition of IH synthesis. An in vitro AKH inhibition of JH III synthe sis was observed, but only at a relatively high concentration (10(-5) M). If the entire AKH content (10(-6) M) Of the CC were released into the medium, the AKH concentration would approach JH synthesis inhibiti ng levels. However, the rate of release of AKH in vitro was very low, and, therefore, AKH from the CC could not affect JH synthesis. In cont rast, a specific JH-esterase, released by isolated CC into the medium, was sufficiently high in both cricket species to account for the obse rved decrease in JH III present. OTFP-sulfone (10(-5) M) restored appa rent IH synthesis of the CA to the control level. There was no reducti on in the amount of JH released when CA were incubated with heat treat ed CC. The CA themselves contained almost no JH-esterase activity. (C) 1997 Wiley-Liss, Inc.