Morphologische Untersuchungen zur Okklusion und Wiedereröffnung proximaler Nierentubuli bei kurzfristiger Ischämie

Plasma membrane shedding and colloid vacuoles in hyperactive human thyroid tissue

The ultrastructural appearance of colloid vacuoles, considered to be a typical sign of hyperactivity in the human thyroid gland, was studied in human thyroid tissue transplanted to nude mice and in human thyroid tissue fixed directly after surgical removal in patients with thyrotoxicosis. Transplanted normal thyroid tissue and toxic diffuse goiter (TDG) tissue was fixed by vascular perfusion with glutaraldehyde 5 or 12 weeks after transplantation. Light microscopic quantification showed that daily injections for 2 weeks of a gamma globulin fraction of patient sera containing thyroid-stimulating immunoglobulins (TSI) greatly increased the number of colloid vacuoles in both types of transplants. The vacuoles were mainly located in the periphery of the follicle lumen, giving the colloid a scalloped appearance. Electron microscopy of TSI-exposed tissue revealed, in addition to colloid vacuoles, the presence of large amounts of membrane material in the follicle lumen. Only sparse amounts of intraluminal membrane material were present in controls. The colloid vacuoles were almost invariably associated with such membrane material, which lined the border between the vacuole and the surrounding colloid. The intraluminal material consisted of spherical and elongated formations, each structure limited by a triple-layered membrane and often containing a dense interior. The elongated structures were often of the same dimensions as microvilli. The apical surface of follicle cells in TSI-exposed tissue expressed numerous microvilli, of which many showed a similar dense interior as the intraluminal membrane structures. The intraluminal membranes frequently showed, like the apical plasma membrane of the follicle cells, a positive reaction for peroxidase. Organelles, such as mitochondria, lysosomes or rough endoplasmic reticulum, were not encountered among the intraluminal membrane structures. These observations indicate that the intraluminal membrane material is derived from the apical plasma membrane of the follicle cells, presumably by shedding of microvilli. A similar association between colloid vacuoles and membrane material was also found in thyroid tissue from patients with thyrotoxicosis fixed directly at operation. It is suggested that the presence of membrane material in the follicle lumen precipitates the formation of colloid vacuoles in hyperactive thyroid tissue. The possible involvement of intraluminal membrane material in the development of microsomal autoantibodies in Graves' disease, i.e. exposure and presentation of thyroid microsomal antigen (identical to thyroperoxidase) to the immune system, is discussed.

Phagocytosis of cytoplasmic blebs derived from smooth muscle cells by fibroblast-like cells and macrophages in the post-partum rat uterus

Numerous blebs were observed in contact with smooth muscle cells (SMC) by light microscopy in the myometrium of the rat uterus after parturition. Electron-microscopically the cell surface of SMC showed bulbous protrusions, which often lacked a basement membrane and were less electron-dense than the surrounding cytoplasm or sometimes nearly electron-lucent. Many bulbous protrusions were separated from SMC and became the isolated structures which we called cytoplasmic blebs. These bulbous protrusions and cytoplasmic blebs were often found to be phagocytosed by fibroblast-like cells and macrophages. A series of these tissue changes in the uterine myometrium after delivery, possibly due to hypoxic conditions, contribute to a rapid involution of SMC which have enlarged during pregnancy.