Parathyroid Hormone-Like Effects of Rainbow Trout Stannius Products on Bone Resorption of Embryonic Mouse Calvariain Vitro*

Products of the Stannius corpuscles (SC) of rainbow trout were tested in an established PTH bioassay involving bone resorption in embryonic mouse calvaria. Aqueous extracts from Stannius corpuscles (SC-homogenate) showed a bone-resorbing activity comparable to PTH in 24-h cultures of calvaria, indicated by a dose-dependent stimulation of lactate production and of calcium, phosphate as well as beta-glucuronidase release. Moreover, SC-homogenates induced an increase in osteoclastic activity. The PTH-like SC-principle is released during in vitro incubations of the glands. These results and the lack of an additive effect of SC-products and PTH on bone resorption suggest that both products activate the same receptor. We hypothesize that the hypocalcemic hormone of the SC of fish shares structural resemblance with PTH, the major hypercalcemic hormone of terrestrial vertebrates.