Changes in the Amounts of the Molt - lnhibiting Hormone in Sinus Glands during the Molt Cycle of the American Crayfish , Procambarus clarldi

The purposes of this study are to determine the molt cycle of the American crayfish, Procambarus clarkit; and to quantify the amounts of the molt-inhibiting hormone (Prc-MIH) in the hemolymph and neurohemal sinus glands during the molt cycle of the American crayfish. The molt cycle was classified into six stages based on the changes in volumes of gastroliths in the stomach and ecdysteroid titers in the hemolymph. A sandwich-type enzyme immunoassay usjng specific antibodies raised against N-terminal and C-terminal segments of Prc-MlH was developed for the Prc-MIH assay. It is sensitive to as little as O.5 fmol of Prc-MtH (3.3 × 1 O-'2 M). In the hemolymph, no Prc-MIH couid 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-stagespecific manner during the molt cycle. It was particularly noteworthy that the initiation of a molting sequence (i,e., entering the early premolt stage) corresponded to the increase in Prc-MIH content in the sinus gland, because the finding is consistent with the hypothesis that crustaceans enter the premolt stage when the MlH secretion from the sinus gland is reduced or ceases.