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It is established that the mandibular organ (MO) of decapod
crustaceans synthesizes and secretes methyl farnesoate (MF). In
this report, MOs of the giant freshwater prawn, Macrobrachium
rosenbergii were investigated by in vitro incubation system.
Products of MO were identified by TLC, GC / MS and HPLC.
Secretion of MF from the dissected MOs confirmed the site of MO
Z祿. rosenbergii. Radiochemical assay (RCA) was used to quantify
in vitro MF synthesis. The rate of MF synthesis in female M.
rosenbergii was 3.0±1.3 pmol / hr / MO. With regard to the
regulation of MF synthesis, the synthetic potential of MF on the
third day of unilaterally eyestalk ablation was about 2.3 times
greater than that of intact. On the other hand, this effect was
reduced by addition of crude eyestalk extract in the medium.
These results suggested that MF synthesis might be modulated by
neuropeptides produced and released from the X-organ sinus gland
complex of the eyestalk. As to the intracellular signal
transduction pathway of the regulation, in vitro treatment of MO
with 8-Br-cAMP (cAMP analog), 8-Br-cGMP (cGMP analog), forskolin
(adenylate cyclase activator) and SNP (sodium nitroprusside,
guanylate cyclase activator) all had inhibitory effect on MF
synthesis. Therefore, cAMP and cGMP might act as second
messengers in the regulation of MF synthesis. According to these
in vitro data, the synthesis of MF should be under some precise
regulation and this MO bioassay system can be a useful tool for
studies on neurohormonal regulation and its signal transduciton.
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