Effects of early hypophysectomy in the aging rat ovary. Ultrastructural study on regression and on delayed epithelial proliferation in the interstitial tissue.

This report describes the fine structure of the "wheel" cells and of epithelial structures which both characterize the interstitial tissue of hypophysectomized and intact senescent rats. The regressive changes induced in normal ovarian interstitial cells of 25-26 day-old hypophysectomized rats were studied from 7 days to 15 months after the operation. They mainly consist in a rapid cytoplasmic dedifferentiation of these steroidogenic cells which, by one month after hypophysectomy, could be only identified by their specific nuclear pattern ("wheel" cells). Further changes of their organelles are only quantitative. These interstitial cells become perennial cells with no ultrastructural signs of senescence. In one year-old animals, the presence of both epithelial testis-like tubes and epithelial cellular cords provides evidence that these structures represent two different morphological arrangements for a similar cellular aspect. Unlike established "wheel" cells, these epithelial structures are evolutive and the thickening of their basement membrane can be considered as an age criterion. The follicular origin of the testis-like tubes and the complex formation of the cords are discussed in the light of our previous photonic study and compared with similar structures occurring in the senile rat ovary and in other situations.