Observations on Mammary Growth in Parabiotic Rats. *

Abstract

Discussion and conclusions

Since estrogen does not stimulate mammary growth in hypophysectomized rats of the age and size of those used in these experiments,^4,5,6 it may be concluded that some pituitary gland substance must have crossed from the partner with hypophysis intact to the hypophysectomized partner and there made possible the mammary growth observed. In this respect the hormone which possesses mammogenic potency is shown to resemble other known pituitary hormones of protein nature. Such passage between parabiotic animals of gonadotropic, adrenotropic and growth hormones has been previously described^7,8,9 and was also observed in the present experiments. The steroid hormone estrogen, on the contrary, failed to be transferred to the partner.⁸ If the pituitary mammotropic substance has a lipoid character as is reported by Lewis and Turner¹⁰ it is perhaps surprising that its behavior in parabiosis seems to link it more with the protein hormones than with the chemically more similar estrogen.

Since the pituitary gland of one rat was serving both members of a pair the amount of mammotropic factor which crossed to the hypophysectomized partner must have been small; yet this quantity was sufficient to alter the mammary response to estrogen from an unqualified negative to a definite positive. Furthermore the fact that the greatest mammary growth occurred where a female was furnishing the mammotropic hormone to the hypophysectomized parabiont suggests a sex difference in production and release of this hormone.