On the Control of Prolactin and Growth Hormone Synthesis in Rat Pituitary Glands1

Pituitary gland prolactin and growth hormone content are decreased in rats bearing certain hormone-secreting pituitary tumors. The present study shows that this is the result of decreased hormone synthesis and not increased release of pituitary gland hormones. Pituitary glands were incubated in vitro in tissue culture Medium 199 containing leucine-4,5-3H. Aliquots from pituitary gland homogenates and incubation medium were subjected to polyacrylamide gel electrophoresis and the optical density and radioactivity in the protein bands measured. The synthesis of hormones was observed for varying time periods up to 21 hr. Labeled prolactin appears in the medium promptly and is not retained in the gland, whereas growth hormone is largely retained in the gland. Both hormones are synthesized at comparable rates. Glands from rats with tumors MtTW5, StW5 or 7315a synthesized prolactin at a rate approximately 50% that found in control glands. No change in the pattern of prolactin release was found in glands from tumor rats. The synthesis of growth hormone was reduced in rats with growth hormone-secreting tumors (MtTW5 43%; StW5 24%) but not in rats with 7315a (prolactin-and ACTH-secreting). No change of growth hormone release was found in glands from tumor rats. The data suggest that tumor hormones decrease pituitary gland hormone synthesis directly at the pituitary level. (Endocrinology83: 799, 1968)