Ultrastructural study concerning disintegration of fibrin foam used as filling material after partial hypophysectomy in rats

Appearance of the cyst- or ductule-like structures and their role in the restoration of the rat pituitary autograft

The anterior pituitary glands of 31-day-old male rats were autotransplanted under renal capsule. At the 3rd and 5th day after transplantation, the autografts were observed by electron microscopy and by immunohistochemistry using antiserum against S-100 protein, which serves as marker of folliculo-stellate (FS) cells. On the 3rd day, a large of the graft was replaced with loose connective tissue in which the FS cells were remarkable in number. The FS cells encircled a small number of granular cells and formed cyst- or ductule-like structures with neighboring FS cells. Together, FS cells and the encircled granular cells formed a basement membrane surrounding the entire ductule. Throughout the regenerating gland, many such ductules were found. On the 5th day, both granular cells and FS cells increased in number. The above observations suggest that FS cells may play an important role in the restoration of degenerated pituitary glandular tissues during the early stage of the transplantation.

Ultrastructural examination of the regeneration of the rat adenohypophysis after partial hypophysectomy

Male Wistar rats were partially hypophysectomized and sacrificed at intervals of from 2 days to 1 year following the operation. The resected material was examined under the light microscope and the residual pituitary under the light and electron microscope. Neither regeneration nor an anatomical restoration of the adenohypophysis occurred even one year after partial hypophysectomy. An increased number of small chromophobe stem cells and juvenile chromophil cells were found in the residual pituitary. The amount of mitoses were not significantly increased. The ACTH, FSH and prolactin producing cells demonstrated electron microscopically distinct changes which were interpreted as signs of intensified activity. This can be seen as a "functional regeneration" to maintain vital pituitary function for the organism.