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 part 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.