Evidence in Vivo and in Vitro of a Role for the Pituitary in the Growth of Malignant Lymphomas in Nb Rats

The growth of a transplantable malignant lymphoma in Nb rats, the Nb 2 node, was accelerated in rats bearing an estrogen pellet and, in particular, in rats bearing transplanted tumors of the anterior pituitary gland. "Lymphoma cell growth-promoting activity" in the sera from the rats was detected and assayed using cultures of Nb 2 node cells. The "activity" of the sera paralleled the degree to which lymphoma growth was accelerated in the animals. Serum from normal rats at a concentration of 1% was moderately active in stimulating culture growth; serum from estrogenized rats was at least 10 times more active; serum from rats bearing pituitary tumors was extremely active and stimulated growth even at a concentration of 0.001% (1:10(5) dilution). In contrast, serum from hypophysectomized rats was devoid of activity, even if the animals were estrogenized. The evidence indicates (a) that the growth of the lymphoma in Nb rats was stimulated by factor(s) in the peripheral blood, the levels of which were subject to control by the pituitary, and (b) that estrogen stimulated lymphoma growth indirectly, through the pituitary gland.