Effect of heparin on oestradiol-induced cell growth and proliferation in the uterus of ovariectomized rats

The aim of this study was to examine the role of heparin in the realization of oestradiol (OE2) effects in the uterus. Ovariectomized rats were treated with a single injection of OE2 dipropionate (10 mu g/rat, i.m.) along with injections of heparin (in doses of 0.4 mg/rat, i.m.). OE2 effects in the uterus were determined by measuring mitotic indices, proliferating cell nuclear antigen (PCNA)-labelling indices, DNA content, and volumes of cells, nuclei and nucleoli in luminal and glandular epithelia and stromal cells of the endometrium 24, 36 and 48 h after the injection of OE2. Heparin treatment inhibited the OE2-stimulated increase in mitotic activity and DNA content of the uterine structures, whereas OE2-induced increases in cell, nucleus and nucleolus volumes in all uterine structures tested at all the times were greatly augmented by heparin. The OE2-induced increase in PCNA-labelling index in all the cell types had a tendency to increase as the result of heparin action. In the absence of OE2, heparin had no effect on any of the uterine parameters. The effect of heparin is probably realized via changes in the mechanism of oestrogen action in the uterus. Heparin probably prevents passage of the cells from the G(1) to the S-phase of the cell cycle and prolongation of the G(1)-phase with consequent accumulation of the cells in this phase of the cell cycle. This probably leads to reduction of mitotic activity. Furthermore, cells in G(1)-phase probably prolong their biosynthetic processes causing enlargement of the cell, nucleus and nucleolus volumes.