MELENGESTROL ACETATE-INDUCED EXUBERANT ENDOMETRIAL DECIDUALIZATION INGOELDI MARMOSETS (CALLIMICO-GOELDII) AND SQUIRREL-MONKEYS (SAIMIRI-SCIUREUS)

Gross appearance, histopathology, electron microscopy, immunohistochem istry, and bacteriology of uteri from 17 melengestrol acetate (MGA)-im planted Goeldi's marmosets (Callimico goeldii), three MGA-implanted sq uirrel monkeys (Saimiri sciureus), and four nonimplanted Goeldi's marm osets were evaluated. The marmosets were first implanted at 1-7 yr of age with 88-267 mg/kg MGA, and the squirrel monkeys were implanted at 5-12 yr of age with 109-376 mg/kg MGA. Implants remained in marmosets for 2-7 yr and in squirrel monkeys for approximately 3.5 yr. Three MGA -implanted marmosets were ovariohysterectomized because of clinical si gns related to uterine lesions. Other samples were obtained via laparo tomy or postmortem. In all MGA-implanted marmosets, the uteri were gro ssly enlarged, firm, and distended with desiccated, friable material. Histologically, uterine lumina contained massive amounts of necrotic d ebris merging peripherally with proliferative endometrial stromal cell s. The endometrium consisted of multinodular crowded sheets, cords, an d papillary projections of large stromal cells with proliferations oft en thicker than the distended myometrium and with obliteration of glan ds and normal architecture. The stromal cells had large, irregular, ve siculated nuclei with moderate numbers of often bizarre mitotic figure s, abundant and vacuolated cytoplasm, often indistinct cytoplasmic bor ders, and occasional intercellular bridges. There was random invasion of underlying myometrium with occasional remote, deep, isolated nests of cells. Lesions were often accompanied by severe infiltrates of prim arily neutrophils. Biopsies of all nonimplanted marmosets were histolo gically normal. Immunohistochemical examination revealed multifocal im munoreactivity for vimentin within proliferative stroma and no reactiv ity for cytokeratin and desmin. The proliferative cells ultrastructura lly had features consistent with decidualized endometrial stroma. Aero bic bacterial cultures of eight implanted marmosets were negative. All implanted squirrel monkeys had similar lesions but with less necrotic debris and suppuration and only slight invasion. The lesion was terme d exuberant decidualization, and we concluded that MGA implantation ca used the lesion in the marmosets and probably caused the similar lesio n in the squirrel monkeys. The use of MGA for long-term contraception in Goeldi's marmosets should be discouraged because it will almost cer tainly result in exuberant decidualization and may result in clinicall y apparent disease. The use of MGA in squirrel monkeys should also be discouraged, and any implanted animals should be closely monitored. Th e development of nonsteroidal birth control measures should be pursued .