TABLE D-4 Effect of Median Eminence Lesions on Prolactin Levels and Mammary Tumors in Rats

 

Effect

Treatment

Prolactin

Percent Tumors

Control

50.9

19.0

Median eminence

179.8

52.2

SOURCE: Welsch et al., 1970.

cinogenicity in mice, rats, and beagles. It is now agreed that estrogen-induced mammary tumors in rats and mice are caused by increased levels of prolactin, which are a consequence of estrogen-induced benign pituitary adenomas. Thus, Welsch (1970) showed that lesions in the hypothalamus of the rat that destroyed inhibitors of pituitary prolactin release led both to increases in levels of prolactin and increases in malignant mammary tumors (Table D-4). Subsequently, Welsch (1977) showed that estrogen-induced mammary tumors in mice are prevented by simultaneous administration of a prolactin inhibitor, 2-bromo-α-ergocryptine (Table D-5). This prolactin inhibitor also prevented mammary tumors caused by simultaneous administration of estrogen and progestogen (Table D-6).

Studies in beagles have implicated progestogen-induced elevations in growth hormone in the pathogenesis of mammary tumors seen in experiments in dogs. Similar to the studies in rats and mice, this link rests first on the demonstration that progestogens that cause mammary tumors elevate growth hormone levels (Table D-7; Concannon et al., 1980). Later, El Etreby and coworkers (1989) showed that inhi

TABLE D-5 Mammary Tumors in Mice After Treatment with Estrogen Alone and Estrogen Plus Prolactin Inhibitor a

Treatment

Percentage with Tumors

Control

11.0

Ethinyl estradiol

27.3

Ethinyl estradiol + CB-154 a

9.0

a CB-154 = 12-bromo-α-ergocryptine.

SOURCE: Welsch et al., 1977.



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