Induction of nucleolar changes in rat luminal cells by single injection or low-dose infusion of estradiol

Abstract

The nucleolar area of rat uterine luminal epithelial cells was measured for 41 h after beginning either of two dosage regimens of estradiol (E2): a single injection of 1.0 μg E2 or a continuous infusion of E2 at a rate of 1.0 μg/24 h. In response to a single injection of E2, mean nucleolar area was significantly elevated above control levels by 10 h. Nucleolar morphology showed slight changes, but the fibrillar component was always associated with 2–3 fibrillar centers by 10 h. In response to a continuous infusion of E2, mean nucleolar area was elevated by 10 h, reached a maximum by 18 h, and remained relatively constant thereafter. Nucleolar morphology showed significant changes by 10 h; the fibrillar component was numerically denser. Bivariate histograms of nuclear versus nucleolar areas showed a bimodal distribution after both injection and infusion, suggesting that two size classes of nuclei existed after estrogen stimulation. The results suggest that: 1) a continuous infusion of E2 at a rate of 1.0 μg/24 h was more effective in inducing larger increases in nucleolar area and transcription than a single injection of 1.0 μg E2 at time 0; 2) using analysis of nuclear and nucleolar areas two subpopulations of cells were identified; and 3) continuous infusion of E2 produced a steady state of ribosome production and cytoplasmic transport by 18 h.