Ultrastructural visualization of protein-4 binding insulin-like growth factors in cow ovarian follicles

Protein-4 that binds the insulin-like growth factors (IGFBP-4) was visualized in the basal membrane of some vessels and follicles and in extracellular membrane surrounding thecal cells in middle-sized cow ovarian follicles. Examinations of serial sections of thecal granular cells showed highly specialized sites for detection of this protein on plasma membranes and highly specialized endosomes responsible for accumulation of IGFBP-4 in granular cells. These data point to an active role palyed by the extracellular ovarian matrix in the binding and accumulation of insulin-like growth factor and to high specificity of internalization and exocytosis of IGFBP-4 by ovarian granular cells. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 126, No. 12, pp. 676–680, December, 1998