Five adult goats were hypophysectomized during lactation; within 10 days their milk yields dropped to a fifth or less of the preoperative levels.
The daily milk yield of one of these goats was increased from 10 to 288 ml. by giving daily injections of ox anterior-pituitary extract; the yield of a second goat was increased from 110 to 1315 ml. by daily injections of sheep anterior-pituitary extract. Treatment of the three other goats with purified anterior-pituitary hormones, corticoids, insulin and triiodo-l-thyronine increased their milk yields from 230, 10 and 45 ml./day to 1480, 1320 and 270 ml./day, respectively.
Milk secretion was induced in the right udder-half of a sixth animal—which had been hypophysectomized in mid-pregnancy and had aborted—by the local injection of prolactin into the parenchyma of the right udder-half plus the systemic injection of somatotrophin; general lactation was subsequently induced and maintained by systemic treatment with prolactin, somatotrophin, adrenocorticotrophin, corticoids, insulin and triiodo-l-thyronine. The maximum daily yield of the animal was 625 ml.
Prolactin and somatotrophin appear to be major components of the lactogenic and galactopoietic complexes in the goat, but further study is required to determine their relative importance and to confirm a preliminary observation that lactation may proceed in the hypophysectomized goat at least for a time by treatment with hormone combinations which include somatotrophin but not prolactin.
A marked increase in water intake of one hypophysectomized goat appeared to be associated with the administration of somatotrophin.
The possibility of species specificities existing in relation to prolactin are discussed.