Changes in the amounts of the molt-inhibiting hormone in sinus glands during the molt cycle of the American crayfish, Procambarus clarkii

The purposes of this study are to determine the molt cycle of the American crayfish, Procambarus clarkii, and to quantify the amounts of the molt-inhi biting hormone (Prc-MIH) in the hemolymph and neurohemal sinus glands durin g the molt cycle of the American crayfish. The molt cycle was classified in to six stages based on the changes in Volumes of gastroliths in the stomach and ecdysteroid titers in the hemolymph. A sandwich-type enzyme immunoassa y using specific antibodies raised against N-terminal and C-terminal segmen ts of Prc-MIH was developed for the Prc-MIH assay. It is sensitive to as li ttle as 0.5 fmol of Prc-MIH (3.3 x 10(-12) M). In the hemolymph, no Prc-MIH could be detected at any of the molt stages tested. However, in the sinus gland, it was demonstrated that the amount of Prc-MIH changes in a molt-sta ge-specific manner during the molt cycle. It was particularly noteworthy th at the initiation of a molting sequence (i.e., entering the early premolt s tage) corresponded to the increase in Prc-MIH content in the sinus gland, b ecause the finding is consistent with the hypothesis that crustaceans enter the premolt stage when the MIH secretion from the sinus gland is reduced o r ceases.