Dynamic changes of myometrial activity, levels of PGF2 alpha and E2 in rabbits after insertion of four types of IUDs.

Myometrial activity, levels of PGF2 alpha and E2 in uterine flushings were measured in rabbits before and after insertion of four types of IUDs. The results showed that IUDs could increase the uterine contraction during the early stages of insertion. Thereafter, the uterine activity tended to be stable. The sequences of uterine contractility generally were: Cu-IUD greater than SS-IUD greater than LNG-Cu-IUD greater than LNG-IUD. The measurement of prostaglandins, determined by RIA, indicated that the concentrations of PGF2 alpha and E2 in Cu-IUD and SS-IUD groups were higher than those of controls for the early phase of insertion, which was not found after four months of use. Our results suggested that hyperactivity of the uterus in the early stage after insertion of IUDs might be relevant to side-effects like expulsion and pain. Copper released by Cu-IUD stimulates the uterine activity partially through increasing PGF2 alpha and E2 contents. In rabbits wearing LNG-IUD or LNG-Cu-IUD, both PGF2 alpha and E2 levels were low. The relatively low uterine mechanical and electrical activities were also observed in these two groups. Based on these data, it is concluded that development of LNG-Cu-IUD is feasible for reducing expulsion of IUDs.