The Persistence of Endometrial Cysts Induced by Oestrogen in Guinea Pigs

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Abstract
Cystic glandular hyperplasia of the endometrium was induced in castrate and entire guinea pigs by injecting estradiol (15 [mu]g./wk.), or by feeding estrogenically potent subterranean clover, for 7-8 weeks. The presence of the lesion was detd. by removal of 1 uterine horn at biopsy from some of the animals at the end of the 7-8 weeks, after which all animals were left untreated for a further period of 20 weeks. In entire animals not subjected to biopsy, cystic endometrial glands were present at the end of the 2nd period in 6 of 8 injd. with estradiol, and in 3 of 5 fed on clover, while all 8 un-dosed guinea pigs had normal uteri. The difference between dosed and undosed groups was significant (P < 0.01). In guinea pigs subjected to biopsy, cystic glands were found at autopsy in 6 of 8 undosed animals, but only 3 of 8 estradiol-treated animals and none of 5 clover-fed animals had the lesions. The difference between dosed and undosed groups was significant (P< 0.05). The uterine horns removed from the 8 undosed animals at biopsy were histologically normal. The lesion was more severe in castrate than in entire animals, and was particularly noticeable in the clover-fed groups. Significant regression of the lesions between biopsy and autopsy occurred in the non-ovariectomized, estrogen-treated groups, but not in the ovariectomized, estrogen-treated groups. Observations were also made on estrous periods and nipple lengths during the expt. and on uterine size and the gonado-tropic hormone content of the pituitaries at the end of the expt. Estrus, as judged by the patency of the vagina, was continuous during the estrogen treatment. Soon after the cessation of treatment, normal cycles were resumed in 11 of the 13 animals not subjected to biopsy or ovariectomy. Endometrial glands that become cystic under the influence of estrogen can remain so for long periods after the cessation of estrogenic stimulation and in the absence of a persisting endocrine imbalance.