Hormonal Properties of Transplanted Pituitary Tumors and Their Relation to the Pituitary Gland

Abstract

Pituitary tumor MtTW5, which secretes growth hormone and prolactin, causes growth of a hormone-dependent mammary tumor and development of the mammary gland. A variant of this tumor has arisen which is devoid of mammogenic activity but has retained somatotrophic activity. The parent tumor (MtTW5) and another prolactin-secreting tumor (7315a) caused large increases in the uptake of 1131 Dy the mammary gland, but this was not apparent in rats bearing the variant strain of tumor (StW5). The luteotrophic hormone secreted by MtTW5 and 7315a was demonstrated by counting the number of corpus luteum cell nuclei per .0306 mm2. Ovaries from rats bearing these tumors had 40% fewer nuclei than nontumor rats or those bearing StW5. Increased somatotrophic hormone secreted by MtTw5 and StW5 was demonstrated by an increased rate of body growth and an enlarged tibia epiphysial cartilage plate. Pituitary gland weight expressed/100 g body weight was significantly less in rats bearing MtTW5 and StW5 than in nontumor rats. Nucleic acid analysis of these tissues showed that the presence of a pituitary tumor decreased the ribose/deoxyribose ratio in the pituitary gland. Homogenates of pituitary glands from tumor and nontumor rats were subjected to electrophoretic separation on polyacrylamide gel. The prolactin and growth hormone bands present in the hypophyses of nontumor rats were virtually nonexistent in the pituitary glands of rats bearing MtTW5. Pituitary glands obtained from rats bearing StW5 had a reduced intensity of the growth hormone band and an increase in the prolactin band. In contrast, virtually no prolactin band and a decreased staining of the growth hormone band were found in pituitary glands obtained from rats bearing 7315a. These studies support the thesis that tumor mammotrophic and somatotrophic activities are associated with separate proteins. These studies also show that pituitary tumor hormones exert a dramatic effect on the host''s pituitary gland growth hormone and prolactin content.