Studies on the origin of ovarian interstitial tissue and the incidence of endometrial hyperplasia in domestic and feral cats

Ovarian interstitial cells (OICs) are a common feature of mammalian gonads but little is understood concerning their origin or functional significance . This study investigated the development and steroidogenic potential of OI C in feral and colony-reared feline queens. Reproductive tracts, collected from a total of SO female colony and feral cats, were fixed and analyzed by morphometry. Ovarian sections were also immune-stained for the expression of the steroidogenic enzymes 17 alpha-hydroxylase/17,20 lyase cytochrome P4 50 (P450c17), 3 beta-hydroxysteroid dehydrogenase/Delta 5-Delta 4 isomerase (3 beta-HSD), and aromatase. These findings were related to serum estradio l and testosterone concentrations and to the degree of existing cystic endo metrial hyperplasia (CEH). Feral cats had three times as many OICs as colon y-reared queens (2713 +/- 855 vs 744 +/- 494 cells/mm(2), P < 0.01). These cells were lipid laden and expressed both P450c17 and 3 beta-HSD at levels that were higher than those seen in the theca interna of adjacent follicles . Aromatase expression was undetectable. The pattern of enzyme expression w as consistent with development of interstitial tissue from atretic follicle s and the potential for continued steroid secretion during the anestrum. Th e incidence of CEH was higher in older (>5 years old; 88.2%) than in younge r (2-4 years; 30%) colony queens (P < 0.01), whereas no such disease was ev ident in any of the feral cats. Estradiol levels were higher in colony-rear ed than in feral cats, but testosterone levels were not different. These da ta are consistent with the transformation of the theca interna of atretic f ollicles in cats into OICs that retain a similar, or even enhanced, steroid ogenic phenotype. Colony-reared cats exhibit a predisposition to CEH compar ed with feral queens that is associated with elevated serum estradiol conce ntrations. Whether or not OICs somehow prevent the development of uterine d isease or otherwise reflect a gonadal response to reduced negative feedback on the hypothalamic-pituitary axis remains to be determined, (C) 1999 Acad emic Press.