title: Long-term regression of experimental endometriosis in a rat model treated with local application of levonorgestrel-loaded biodegradable microspheres.
abstract: BACKGROUND
  A previous study demonstrated that local application of levonorgestrel-loaded polylactic acid microspheres (LNG microspheres) resulted in significant regression of endometriotic cysts in a rabbit model for 6 months without disturbing the metabolic parameters or ovarian function. In order to investigate the feasibility of local application of LNG microspheres as a long-term maintenance treatment for endometriosis, the suppressive effect of a single intra-cystic injection of LNG microspheres was studied for 1 year in a rat model.
  
  
  RESULTS
  Twenty four rats with experimental endometriotic cysts were randomized to be treated with a single intra-cystic injection of LNG microspheres (n = 8); 6-month GnRH agonist (GnRHa, n = 8) or control (n = 8). Intra-cystic injection of LNG microspheres and GnRHa treatment caused comparable regression and atrophy in endometriotic cysts in the first 6 months. Compared with the control, the wet weight of the endometriotic cysts was significantly lower in both groups at Month 6 but by Month 12 only remained low in the LNG microspheres group (P < 0.01). The immunostaining of estrogen receptors (ERs) in both the epithelium and stroma and progesterone receptors (PRs) in the stroma was significantly weakened in the LNG microspheres group at Month 6 and was not fully restored at Month 12 (P < 0.01). Metabolic parameters and estrous cycle were not disturbed by local application of LNG microspheres.
  
  
  CONCLUSIONS
  In a rat endometriosis model, the suppressive effect of a single intra-cystic injection of LNG microspheres was comparable to that of GnRHa, and was maintained for 1 year. The down-regulation of ERs and PRs might serve as possible mechanism of long-term effectiveness.
authors.affiliation: Department of Obstetrics and Gynecology, No. 451 Hospital of the PLA, No. 269 Youyi East Road, Xían, Shaanxi 710054, China. ypfmmu@gmail.com
authors.forename: Peng
authors.initials: P
authors.lastname: Yuan
authors.forename: Biliang
authors.initials: B
authors.lastname: Chen
authors.forename: Yanhong
authors.initials: Y
authors.lastname: Huang
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Xin
mesh_terms: D020341:Absorbable Implants; D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry; D001835:Body Weight; D004195:Disease Models, Animal; D004715:Endometriosis / Q000188:drug therapy*; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage*; D008863:Microspheres; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011960:Receptors, Estrogen / Q000378:metabolism; D016896:Treatment Outcome
chemical_list: D001672:Biocompatible Materials; D011960:Receptors, Estrogen; D016912:Levonorgestrel