Hormonal Effects on Calcium Metabolism in Crustacea

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Abstract
Cyclic shifts of calcium in the exoskeleton and soft tissues, as they are related to the intermolt cycle in crayfish, are reviewed. Regulatory factors, derived from the eyestalk, influence levels of exoskeletal calcium; eyestalk extracts prepared from animals in premolt decrease shell calcium, while reciprocally extracts from animals in intermolt increase it when these hormonal sources are injected into animals in the premolt stage (D0-D4) . In addition, premolt eyestalk extract results in an increase in gastrolith calcium. In the exchange of calcium between the animal and its environment there is evidence for differentialdeposition of recently available calcium in the exoskeleton. Further, intermolt and early premolt animals maintained in Ca45-labelled water for 15 days concentrate it 4 and 3—fold in the exoskeleton and stomach, respectively. However, removal of a molt-inhibiting factor through ablation of eyestalks results in a 20 and 40—fold increase in incorporation inthese same sites relative to environmental concentrations. Treatment with mammalian parathyroid extract mobilizes both exoskeletal and gastric calciumand leads to a rise in blood calcium. However, there is little or no effect on levels of exoskeletal citric acid. Further, citric acid is higher in the crayfish carapace during stage C, the period of mineralization, than in stage D, the period of demineralization. There are both similarities and differences between the effects of crustacean and mammalianregulating factors with respect to the direction and extent of mineralization. Biochemical studies should elucidate the mechanisms regulated by these hormones.

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