THE ONSET OF ALLOMETRIC MAMMARY GROWTH IN THE FEMALE HOODED NORWAY RAT

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Abstract
SUMMARY: In order to study the factors involved in the initiation of allometric mammary growth, which occurs at about 3 weeks of age in the intact female rat, an attempt to induce this phase prematurely in the suckling gonadectomized animal by means of oestrogen was made. It was found, however, that the mammary glands were practically insensitive to physiological doses of this hormone during the suckling period unless anterior pituitary (a.p.) extract was also given. The relative mammary growth rate in animals treated with a.p. plus oestrogen from the 10th to 27th day of life was similar to that found in control rats receiving oestrogen alone from the 20th to 36th day, but in the former groups allometry was initiated before the 20th day of life. It is suggested that both the level of endogenous oestrogen secretion and the functional activity of the anterior pituitary may be important in determining the time of onset of allometric mammary development in the intact animal.

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