LOBULO ALVEOLAR MAMMARY GROWTH 



INDUCED IN HYPOPHYSECTOMIZED RATS BY 



INJECTIONS OF OVARIAN AND 



HYPOPHYSIAL HORMONES 



TWENTY YEARS AGO, adieiiotrophic, thyrotrophic, gonadotrophic and soina- 

 totrophic functions had already been proven for the pituitary gland by 

 Evans and co-workers. And from these same investigators came the first evi- 

 dence of a corpus luteum-activating or luteotrophic function, now identified 

 with the mammotrophic or lactogenic hormone of the anterior lobe (see Evans' 

 Harvey Lecture^ for review of early work). Mammary-stimulating activity was 

 demonstrable in crude pituitary extracts by Evans and Simpson" and at that 

 time was thought to be due to pituitary gonadotrophic hormone causing the 

 ovaries to secrete the mammary-stimulating female sex hormones, estrin and 

 progestin. Recent experiments from this laboratory^ have shown that the 

 lobulo-alveolar growth induced in intact rats by Evans and Simpson with 

 crude pituitary extracts may be duplicated with purified lactogenic hormone. 

 Here, as in earlier work/ the inclusion of the lactogenic hormone in a gonado- 

 trophic triad along with follicle-stimulating hormone (FSH) and interstitial 

 cell stimulating hormone (ICSH) has seemed advisable since it is capable 

 of causing functional hypertrophy of luteal cells already formed in the ovary. 

 Lactogenic hormone injected into normal rats induces a condition compara- 

 ble to psetidopregnancy, in which (a) a single crop of corpora lutea become 

 hypertrophic and secrete progestin, (b) follicles do not develop to maturity 

 and therfore ovulation is inhibited, (c) the vagina shows a high degree of 

 mucification, (d) the uterus shows progestational changes and will nidate 

 threads, and (e) the mammary glands show lobulo-alveolar development. 

 Since Nelson^'* and others have shown that estrone will bring about these 

 same changes it might be assumed that this hormone causes an increased 

 secretion of lactogenic hormone by the pituitary. Granted that the pseudo- 

 pregnant rat is under the influence of an increased secretion of lactogenic 

 hormone, it might be expected that after removal of the pituitary the injec- 

 tion of that hormone would provide adequate substitution therapy in main- 

 taining the set of conditions just listed. As far as the genital tract is concerned 

 that may be true, but the mammary gland fails to grow to the same degree 

 as in the intact animal. This restilt was foreshadowed in the earlier experi- 

 ments of Evans and co-workers mentioned by Lyons and Pencharz in 1936,' 

 in which gonadotrophic preparations stimulated the ovaries and indirectly 

 the genital tract in hypophysectomized rats, but left the mammary glands 

 atrophic. 



The majority of the many experiments of the past seven years in which at- 



1:317] 



