Treatment of rhesus monkeys (Macaca mulatta) with intrauterine devices loaded with levonorgestrel

The effects of levonorgestrel-loaded plastic intrauterine devices on endometrial morphology were investigated in 15 rhesus monkeys for 14 weeks. The devices were designed to release 25 microgram of the hormone per day and were inserted in the uterus by hysterotomy. Control animals were sham operated or received inert placebo devices. With the levonorgestrel-releasing devices, widespread changes in endometrial morphology were seen. These changes included atrophy of the endometrial mucosal and glandular epithelium and decidualization of the endometrial stroma. With the inert placebo control devices, only minor changes in endometrial morphology were observed.