Direct Effects of a Hypothalamic Extract on Hormone Secretion by a Pituitary Mammo-somatotropic Tumor1

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Abstract
A transplantable rat pituitary tumor (Wig) which secretes large amounts of prolactin and growth hormone (GH), was found to contain very little prolactin/100 mg of tissue but to release large amounts of prolactin into the plasma. Upon incubation for 4 hr, the tumor released about 25 times more prolactin into the medium than was initially present in the fresh tissue. When the tumor was incubated together with rat hypothalamic extract for 4 hr, prolactin release was significantly depressed, whereas GH release was significantly increased. Rat cerebral cortical extract had no effect on release of prolactin or GH by the incubated tumor. These results indicate that hormone secretion by the W15 pituitary tumor can be alteed by the direct action of a hypothalamic extract in vitro, even though the tumor appears to be free of hypothalamic control in vivo.