EFFECTS OF OESTRONE AND PROGESTERONE ON MAMMARY DEVELOPMENT IN THE GUINEA-PIG

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Abstract
SUMMARY Three experiments are described on the effects of oestrone and progesterone over wide dose ranges on the development of the mammary gland in the ovariectomized guinea-pig. Factorial designs were used so that the responses to both steroids could be studied simultaneously. The degree of mammary development was assessed by objective and by subjective methods. The observation of previous workers that complete mammary development could be evoked in the guinea-pig by oestrogen alone was not confirmed. Over a wide dose range of oestrone better development of the gland was obtained if progesterone was also administered. On some dose levels of oestrone the synergistic effects of progesterone were very marked. Maximal mammary development was observed with a daily dose of 10–50 μg oestrone in combination with 1000 μg progesterone. Considerable lobule-alveolar development was observed with progesterone alone when the daily dose was sufficiently high (2400 μg). No histological abnormalities were observed in the glands except in those developed on the lowest dose of oestrone to give significant growth effects (0·1 μg), in which there was some evidence of cystic changes. The significance of the progesterone: oestrogen ratio in mammary development is discussed.

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