Elevated Serum Prolactin Levels after Pituitary-Stalk Section in Man

Prolactin activity, measured by a highly sensitive and specific assay procedure in the serums of 15 patients subjected to surgical section of the pituitary stalk for metastatic breast cancer or for diabetic retinopathy, was undetectable before operation; 11 showed marked elevations of serum prolactin (42 to 508 ng per milliliter) after operation. Normal volunteers, patients with diabetes mellitus or metastatic breast carcinoma not subjected to stalk section and patients subjected to hypophysectomy did not secrete detectable amounts of prolactin. Secretion of prolactin was not an essential feature of either remission or progression of breast carcinoma after pituitary-stalk section. Since immunoreactive growth hormone levels were less than 6 ng per milliliter in these patients, these observations constitute further evidence for the existence of a molecular species of human prolactin distinct from the growth-hormone molecule. The results demonstrate that stalk section usually converts the human pituitary gland into a primarily prolactin-secreting organ.