Regulation of methyl farnesoate in the hemolymph and mandibular organ of the lobster, Homarus americanus

Abstract

Methyl farnesoate (MF) was measured in the hemolymph and mandibular organs (MO) of the lobster. Although a few animals had detectable MF levels in their hemolymph, this compound was undetectable (<0.4 ng/ml) in the hemolymph of most animals. One day after bilateral eyestalk ablation, MF was detected in the hemolymph of all animals, reaching variable levels (2.0–31.2 ng/ml) by the fourth day. Unilateral eyestalk ablation caused a smaller increase in hemolymph levels of MF. Similarly, the MF content of the MO, the only known site of MF synthesis, was low in intact lobsters (8.1 ng/gland) and was elevated in unilaterally and bilaterally eyestalk-ablated animals (54.1 and 106.9 ng/gland, respectively). When extracts of the sinus gland (SG), a source of neuropeptides in the eyestalk, were injected into bilaterally ablated lobsters, hemolymph levels of MF dropped to undetectable levels in 2 to 3 hr. The response to SG extract was dose dependent, and MF levels recovered by 12 to 24 hr after treatment. SG extract also lowered the MF content in the MO from 267.6 to 6.6 ng/gland after 4 hr. These results indicate that MF in the hemolymph and MO is negatively regulated by a factor(s) from the SG.