Correlation between nuclear bodies and estrogen receptors in endometrial epithelial cells of old rats

Nuclear bodies (NB) are prominent round structures in interchromatin regions of interphase nuclei, regarded as markers of stimulated rRNA synthesis. Their frequency was found to be estrogen-dependent and correlated with estrogen receptor (ER) content in endometrial epithelial cells of prepubertal and cyclic rats. The present study was designed to simultaneously examine the frequency of simple and complex NB and the status of ER in endometrial epithelia of old rats in relation to age and vaginal cytology. The vaginal cycles of old Wistar rats (n degree = 24) at 24, 28, 32, and 36 months of age, which were longitudinally monitored for at least 180 days by daily vaginal smears, were extremely irregular with a predominance of either persistent estrus or persistent diestrus over many days, weeks and even months. In all age groups ER-immunoexpression was very high (+3 = > 75%) in persistent-estrus rats and coincided with particularly frequent NB (2-3 simple NB out of 4-5 total NB per nuclear profile) in the tall epithelial cells with ultrastructural signs of intense protein synthesis. In persistent-diestrus rats isolated simple and complex NB (1 per nuclear profile) and an almost absent ER expression were distinctive of the nuclei in low, ultrastructurally "inactive" endometrial luminal and glandular epithelial cells. Thus, ER immunoexpression and NB frequency are also estrogen-dependent in old rats. Our findings show, for the first time, that ER immunoexpression in endometrial epithelial cells is down-regulated only in old rats in persistent diestrus, whereas in persistent-estrus rats intense ER expression harmonizes with high NB frequency, irrespective of animal age.