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Reduction by pituitary isograft of inhibitory effect of large dose of estrogen on incidence of mammary tumors induced by carcinogen in ovariectomized rats
Author(s) -
Nagasawa Hiroshi,
Yanai Reiko
Publication year - 1971
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910080314
Subject(s) - dmba , prolactin , endocrinology , medicine , ovariectomized rat , estrogen , pituitary tumors , 7,12 dimethylbenz[a]anthracene , mammary tumor , estradiol benzoate , mammary gland , pituitary gland , hormone , carcinogenesis , cancer , breast cancer
Interaction of prolactin and estrogen on the incidence of mammary tumors induced by 7,12‐dimethylbenz (a) anthracene (DMBA) in female Sprague‐Dawley rats was studied. Rats were bilaterally ovariectomized at 45 days of age and then treated subcutaneously with 20μg of estradiol benzoate (EB) every 2 days beginning the next morning. They received single intravenous injections of 5mg DMBA at 52 days of age. Two months later they were divided into four groups: Group I received no pituitary grafting: group II was grafted with three isologous pituitaries under the right kidney capsule: groups III and IV received six pituitaries each. EB injections were continued throughout the experiment to every group except group IV. Serum prolactin levels were determined by radioimmunoassay just before pituitary grafting, 20 days, 2 and 3 months after grafting. At the end of 5 months after DMBA injection, the mammary tumor incidence and the number of palpable tumors per tumor‐bearing rat apparently increased, and the percentage of completely regressed tumors decreased in groups II and III as compared to group I. Serum prolactin level was significantly higher in groups II and III than in group I at 3 months after pituitary grafting. Only one rat had palpable mammary tumors in group IV and serum prolactin levels were always significantly lower in this group than in the others. These results indicate that prolactin secreted by the grafted pituitaries overcomes the inhibitory action of a large dose of estrogen on the growth of DMBA‐induced mammary tumors of the rat and results in an increased incidence of the tumors.