ESTROGEN-INDUCED GUINEA-PIG MODEL FOR UTERINE LEIOMYOMAS - DO THE OVARIES PROTECT

A guinea pig model was used to study the hormonal control of uterine l eiomyomas. Twenty female guinea pigs were divided into four groups-you ng, old, ovariectomized (OVX), and non-OVX animals-and were given two estradiol-17 beta (E(2)) silastic implants each for 3-10 mo; another f our older OVX animals served as controls and received empty implants. After 3 mo, 100% (8 of 8) of the OVX animals, but none of the OVX cont rols, developed tumors, mainly on the uterine serosa and the abdominal wall. Electron microscopy and desmin immunostaining demonstrated that the tumors were leiomyomas. In E(2)-treated animals, E(2) levels in s erum, leiomyomas, or leiomyoma-free uterine segments rose significantl y while serum progesterone (P-4) was negligible. Surprisingly, only 8% (1 of 12) of the non-OVX animals developed a tumor. This apparent ''o varian protection'' was transient: after 6-9 mo, 50% of the remaining non-OVX animals developed leiomyomas, but these were smaller and fewer than in OVX animals. On the basis of this model, we propose the hypot hesis that some factors from the ovaries suppress leiomyoma growth in response to estrogen but that as the ovaries age this protection is di minished, allowing the clinical development of leiomyomas.