A New Hormone of the Anterior Pituitary

Abstract

Riddle and Braucher 1 showed that the effective stimulus for the enlargement and functioning (formation of “crop-milk”) of the crop-glands of pigeons is a substance derivable from the anterior hypophysis only; and the luteinizing substance derived from pregnant urine is not that substance. They were unable to decide “whether the principle activating the crop-gland is the growth, the sex maturity, or a third and now unknown anterior pituitary hormone.” We have now shown (a) that the principle which evokes the crop-gland response is a third anterior pituitary hormone, and (b) have identified this same hormone, which we shall here call “Prolactin” as the hitherto undefined pituitary principle which is essential for lactation in mammals.

To prepare this hormone relatively free from the growth and gonad-stimulating principles frozen anterior pituitaries of beef or sheep were ground, defatted with acetone and alcohol and dried. This powder was extracted 3 times in aqueous medium at a pH of approximately 2.5. The acid extracts were precipitated isoelectrically. The isoelectric precipitate was redissolved and reprecipitated 3 times to free it of maturity hormone and then dried with acetone. About 10% of the original weight of dried powder is thus obtained in an acid-soluble isoelectric-insoluble form. The addition (to suspensions) of 0.2% cresol to complete the destruction of the growth principle does not markedly affect the “Prolactin”.

Assays of several of our preparations, and some of the growth and gonad-stimulating extracts of others, have been made on immature common pigeons and ring doves of both sexes. Table I shows only a part of data from male ring doves. The crop-gland response is equally decisive in either species and sex; the gonadstimulating response is more pronounced in males. Neither species has been adequately tested as to its suitability for the assay of the growth hormone; we therefore show here the absence of the “Prolactin” effect from growth hormone preparations of Drs. M. O. Lee and M. K. Schaffer, Boston, who kindly supplied very potent samples assayed on hypophysectomized rats.