Occurrence of genital tract abnormalities and bladder hernia in female mice exposed neonatally to tamoxifen.

Three groups of female C57BL/Tw mice given 5 daily injections of 2, 20 or 100 micrograms tamoxifen (Tx) starting on the day of birth were killed at 35 and 150 days of age. About a half of the mice killed at 150 days had been ovariectomized at 90 days. Uterine hypoplasia, myometrial involution and suppression of the uterine-gland genesis were found in the 2 age-groups of Tx-treated mice. Vaginal hypoplasia and hypospadia were common abnormalities in 150-day-old Tx-treated mice. Vaginal adenosis was encountered in 35-day-old mice treated neonatally with 20 or 100 micrograms Tx, but not in 150-day-old group. Permanent proliferation of vaginal epithelium was not induced by Tx. More than 80% of oocytes in small follicles were degenerated in Tx-exposed mice at 150 days, but not so in those at 35 days. Ovaries of neonatally Tx-exposed mice lacking corpora lutea made no luteinizing response to human chorionic gonadotropin injected prepubertally. Urinary-bladder hernia with or without caecum hernia frequently occurred in 150-day-old mice given 20 or 100 micrograms Tx. The present study revealed that neonatally administered Tx causes various abnormalities in gonad and genito-urinary tract of female C57BL/Tw mice.