Co-localization and secretion of parathyrin of Stannius corpuscles (immunoreactive parathyroid hormone) and of secretory glycoproteins including secretory protein-I in the European eel (Anguilla anguilla L.).

Until recently, teleosts were considered to be devoid of parathyroids. We showed recently that the corpuscles of Stannius, that structurally have features in common with the parathyroid gland, produce a molecule resembling mammalian parathyroid hormone (PTH). We refer to this molecule as parathyrin of corpuscles of Stannius (PCS). Parathyroid secretory protein-I (SP-I) is an acidic glycoprotein, probably identical to adrenal chromogranin A, that is co-stored and co-secreted with PTH. In the present study, PCS was localized in secretory granules of fresh water eels by immunocytochemistry. In addition, several glycoproteins were identified in these granules by periodic acid-Schiff staining and/or concanavalin A lectin binding. One of the glycoproteins that was positive with periodic acid-Schiff, but not with concanavalin A, cross-reacted with antisera to bovine parathyroid secretory protein-I. When the eels were made hypercalcemic by injecting calcium or pituitary extract, there was a coincidental translocation of the PCS, immunoreactive SP-I and the glycoproteins, suggestive that these granules were undergoing exocytosis. Immunoblot analysis of saline extract of the corpuscles of Stannius confirmed that immunoreactive SP-I was present in the tissue. It exhibited a molecular mass of about 55 kDa compared to about 70-80 kDa exhibited by mammalian SP-I when analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis.