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Experimental Initiation of Milk Secretion in the Albino Rat^*

Department of Dairy Husbandry, University of Missouri, Columbia, Mo.

ABSTRACT

Additional experimental evidence is reported in support of the theory that the growth of the mammary duct system is stimulated by the estrogenic hormone theelin; that the lobular system is stimulated by theelin and corporin; and that the secretory activity is initiated by a hormone from the pituitary. The presence of numerous follicles in infantile rat ovaries suggests that the estrogenic hormone may be secreted by these ovaries and thus be responsible for the duct development in the immature female.

The positive tests for theelin obtained from extracts of urine and feces of male rats indicate that some organ in the male elaborates the estrogenic hormone which is believed to be responsible for the rather extensive duct development occurring in the male rat gland.

Mammary gland development induced by a pseudo-pregnant condition indicates that full development of the duct system and lobules occurs during the first half of pregnancy.

The estrogenic hormone alone seems incapable of initiating milk secretion or of conditioning the gland so that pituitary extracts can stimulate the gland to secretion.

Milk secretion is induced in normal females by subcutaneous implants of fresh pituitaries from either male or female donors. In spayed females the presence of theelin and corporin was necessary before milk secretion was brought about by pituitary implants.

The extract of sheeps' pituitary was able to induce secretory activity in either spayed or normal females only when theelin and corporin were injected with the galactin.

^* This study has been aided in part by a grant from the Committee on Grants-in-Aid of the National Research Council.

"Contribution from the Department of Dairy Husbandry, Missouri Agricultural Experiment Station Journal Series No. 345."