Radioimmunoassay of Epidermal Growth Factor

Epidermal growth factor (EGF) is a biologically active polypeptide extracted from male mouse submaxillary glands. It exists either alone or complexed with an arginine esterase. It causes generalized epidermal growth and keratinization in the immature mouse and results in precocious tooth eruption and eye-opening that are the basis for an EGF bioassay. EGF is also active in a variety of epithelial tissues from several other species. A rapid and sensitive solid phase radioimmunoassay for EGF has been developed in which rabbit antibody to EGF was adsorbed onto the walls of nylon vessels. After 24 hr of incubation, 125I-labeled EGF was displaced by as little as 30 pg of unlabeled EGF. There was no cross-reaction with the arginine esterase; mouse nerve growth factor; rat growth hormone or prolactin; human growth hormone, ACTH, FSH, LH or TSH; beef or pork insulin; or angiotensin I. Immunoreactive EGF concentrations in submaxillary glands of immature, 15-dayold male mice were very low (0.016 ng/mg of wet tissue), but rose exponentially with increasing age to reach adult levels (1000 ng/mg) in mice 50 days old or more. Sex and androgen dependence were demonstrated by the finding that normal females and castrated males had submaxillary gland EGF levels (70 ng/mg and 113 ng/mg, respectively) undetectable by bioassay and much lower than the levels of normal males and testosterone- treated females (1000 ng/mg and 2900 ng/mg, respectively). These studies have confirmed and extended the results obtained with the bioassay. The solid phase EGF radioimmunoassay is sufficiently rapid and sensitive to permit further studies of EGF physiology in the mouse. (Endocrinology90: 1261, 1972)