Suppression of Pituitary Gland Hormone Content by Pituitary Tumor Hormones1

Pituitary tumors that secrete combinations of growth hormone, prolactin and ACTH were transplanted into female rats and the pituitary glands of the hosts were examined to ascertain any change in hormonal content. The size of the pituitary gland was decreased in tumor-bearing rats. Implantation of tumor MtTW5, which secretes prolactin and growth hormone, caused a decrease in the growth hormone, prolactin and TSH content; however, the ACTH content was increased. These findings were compared with those from the pituitary glands of rats with StW5, a growth hormonesecreting tumor which caused a decrease in the growth hormone content but did not affect either the prolactin or TSH. When rats were implanted with 7315a, a tumor which secretes prolactin and ACTH, the pituitary gland content of prolactin was decreased but that of growth hormone was normal. It is concluded that an exogenous source of pituitary hormones decreases pituitary gland function by selectively decreasing the concentration of analogous pituitary gland pep tides, and through a less specific mechanism decreases the TSH content but increases that of ACTH. Although a growth hormone-and prolactin-secreting tumor MtTW5 increased the pituitary gland ACTH concentration, no apparent increase in secretion of this peptide occurred since host rats had normal resting blood corticosterone levels and responded normally to ether stress. (Endocrinology 82: 889, 1968)