Cyclic nucleotide regulation of methyl farnesoate synthesis by the mandibular organ of the lobster, Homarus americanus

Mandibular organ (MO) synthesis of methyl farnesoate (MF) is negatively regulated by extracts of the sinus gland, a neuroendocrine organ in the lobster eyestalk. Sinus gland extracts significantly increased cyclic GMP (cGMP) levels in the MO in vitro, but had no effect on cyclic AMP (cAMP) levels. Extracts of two other neuroendocrine tissues, the brain and thoracic ganglion, did not affect either cAMP or cGMP levels. In vitro treatment of MO with 8‐bromo‐cGMP (a cGMP analog) significantly decreased MF synthesis at concentrations of 10−7 M to 10−4M. Higher concentrations of 8‐bromo‐cAMP (10−5M to 10−4M) were required for significant decreases in MF synthesis. Forskolin and IBMX decreased MF synthesis at a concentration of 10−5M, but had no effect at lower concentrations (10−8M to 10−6M). These data suggest that cGMP is a second messenger for the sinus gland factor that inhibits MF synthesis in the MO. © 1993 Wiley‐Liss, Inc.