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Experimental Studies of Factors Influencing Hepatic Metastases

XIV. Effect of Prolactin^*

( Departments of Pathology and Surgery, Division of Surgical Research, University of Pittsburgh, Pittsburgh, Pennsylvania)

Intraperitoneal administration of ovine prolactin increased the incidence and size of hepatic metastases in hypophysectomized female rats following intraportal injection of Walker tumor cells. Such treatment increased the size but not incidence of tumors in intact females and had no effect on either parameter in intact or hypophysectomized males. Prolactin elicited ductal and end-bud mammary growth only in hypophysectomized females and in addition lobulo-alveolar proliferation in intact females and to a moderate degree in intact males. Other tropic effects were not evident in either sex. These findings indicate that prolactin represents a significant factor for the establishment and growth of hepatic metastases in female rats in the experimental model utilized. Possible mechanisms of action of prolactin in this regard are discussed.

Unlike previous experience with extracts of fresh rat pituitary glands, those obtained from beef, sheep, and humans failed to influence tumor growth in hypophysectomized female rats. These heterologous preparations exhibited somatotropic, variable gonadotropic, but no mammogenic activities. Considerations including species specificity and qualitative and quantitative factors which might account for these divergent effects on tumor growth are noted.

^* Supported by the American Cancer Society.

Received 4/24/63.