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Inhibition of Ovariectomy-induced Rat Mammary Tumor Regression by a Mammosomatotropic Tumor¹

Research Institute of the Hospital for Joint Diseases, Mount Sinal School of Medicine, New York, New York 10035

Growth of the transplantable rat mammary carcinoma, MTW9, is stimulated by elevated serum prolactin concentrations. MTW9 grown in rats with high serum prolactin produced by coimplantation of a mammosomatotropic tumor, MtTW10 (MTW9-MtT), does not regress after ovariectomy (OVEX). MTW9 grown in rats with high serum prolactin produced by daily administration of perphenazine (MTW9-P) does regress after ovariectomy whether perphenazine treatment is continued (MTW9-P) or not (MTW9-PD).

Experiments were designed to determine whether some hormonal abnormality in MtTW10-bearing rats might prevent OVEX-induced mammary tumor regression. The hormone environment of hosts bearing MtTW10 was simulated in rats bearing MTW9-PD. High doses of adrenocorticotropic hormone, growth hormone, 17-hydroxyprogesterone caproate, and prolactin failed to inhibit OVEX-induced regression. A high dose mixture of prolactin, adrenocorticotropic hormone, and growth hormone administered to a limited number of rats produced extreme mammary stimulation but also failed to inhibit tumor regression. Implantation of MtTW10 into animals bearing MTW9-PD prevented OVEX-induced regression of mammary tumor.

These data are consistent with secretion of a factor other than prolactin, growth hormone, adrenocorticotropic hormone, or progestin, which inhibits OVEX-induced regression, although some combination of hormones present in MtTW10-bearing rats cannot be eliminated.

¹ This investigation was supported by Grants P 30 14194 and CA 10064 awarded by the National Cancer Institute, Department of Health, Education, and Welfare.

² To whom requests for reprints should be addressed.

Received 10/ 7/77. Accepted 4/27/78.