title: Morphometry on the rat thyroid gland: evaluation of the apical plasma membrane (microvilli and zonula occludens) in freeze-fracture replicas under different functional conditions.
abstract: Morphometry was employed on freeze-fracture replicas of the rat thyroid gland following long-term TSH stimulation and hypophysectomy. Our results demonstrate two conspicuous alterations of the luminal (apical) plasma membrane in comparison to normal control specimens: firstly there is an augmentation of surface area after TSH administration which is related to the novel formation of microplicae (pseudopods), but not an increase in the total number of microvillous structures per unit area. In addition an occurrence of numerous endocytic invaginations is observed. Secondly the zonula occludens reveals a loosening of its reticular structure by showing wider meshes without increase in discontinuities of ridges (grooves respectively) following activation of the thyroid gland. These ultrastructural features corroborate electrophysiological findings of an increase in capacitance and a rapid fall of the transepithelial resistance in TSH stimulated thyroid follicle cells.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D005260:Female; D005614:Freeze Fracturing; D007016:Hypophysectomy; D008854:Microscopy, Electron; D008871:Microvilli / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D013961:Thyroid Gland / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D013972:Thyrotropin / Q000494:pharmacology
chemical_list: D013972:Thyrotropin