The ultrastructural features of progestagen-induced decidual cells in the rhesus monkey (Macaca mulatta).

Five rhesus monkeys were treated with levonorgestrel-releasing intravaginal rings for 52 weeks. The rings were designed to provide a sustained release of ten times the human dose level of the hormone. Histological examination of the uterine endometrium showed widespread decidualisation of endometrial stromal cells. Ultrastructurally, two distinct cell types were identified: decidual and granular. Some of the decidual cells were ultrastructurally comparable with those reported elsewhere; however, in aproportion of these cells, intracisternal sequestration of the rough endoplasmic reticulum was widespread. The granular cells resembled those described in the metrial gland of rats and, as their name suggests, contained variable numbers of electron-dense granules.