title: Ultrastructure of thyroid C cells in sheep treated with vitamin D3.
abstract: Ultrastructural observation was performed in C cells of sheep injected intramuscularly with a dose of 2 million IU of vitamin D3 daily for 10 days, 20 days and 30 days, respectively. After treatment with vitamin D3, hyperplasia and hypertrophy of C cells were noticed mainly at the periphery of the thyroid follicles. Most of hypertrophied C cells degranulated conspicuously and contained many prosecretory granules near the well developed Golgi apparatus which were in the actively secreting and packaging phase of their secretory cycle. The other C cells had prominent lamellar arrays of rough-endoplasmic reticulum and aggregations of free ribosomes in the cytoplasm which were interpreted to be in the actively synthesizing phase of their secretory cycle. Atrophic C cells which contained degenerative organelles in the cytoplasm were occasionally observed among the hypertrophied C cells. The present ultrastructural findings clarified that C cells synthesize and secrete calcitonin continuously due to prolonged hypercalcemia induced by long-term administration of excessive doses of vitamin D3 in sheep.
authors.affiliation: Department of Veterinary Pathology, School of Veterinary Medicine, Rakuno Gakuen University, Hokkaido, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Okada
authors.forename: E
authors.initials: E
authors.lastname: Saito
authors.forename: K
authors.initials: K
authors.lastname: Matsukawa
mesh_terms: D000818:Animals; D002762:Cholecalciferol / Q000008:administration & dosage / Q000494:pharmacology*; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000187:drug effects / Q000648:ultrastructure; D006965:Hyperplasia; D006984:Hypertrophy; D007273:Injections, Intramuscular / Q000662:veterinary; D008297:Male; D008854:Microscopy, Electron; D008928:Mitochondria / Q000187:drug effects / Q000648:ultrastructure; D012270:Ribosomes / Q000187:drug effects / Q000648:ultrastructure; D012756:Sheep / Q000033:anatomy & histology*; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000648:ultrastructure*
chemical_list: D002762:Cholecalciferol