OBSERVATIONS ON THE EFFECTS OF PREPARTAL AND POSTPARTAL ESTROGEN AND PROGESTERONE TREATMENT ON LACTATION IN THE RAT

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Abstract
Observations were made on the effects of prepartal and postpartal admn. of estrogens, of progesterone and of the combination on lactation in intact and in ovariectomized rats, using the growth rate of nursing young to indicate the rate of milk secretion. Daily (200[mu]g.) treatment with estrone or diethylstilbestrol dipropionate begun on the 2d day of lactation does not inhibit milk secretion in ovariectomized rats while moderate daily (5 [mu]g. and 10 [mu]g.) injn. of estrone inhibits lactation in intact rats, the inhibition appearing 10-12 days after the beginning of treatment. The inhibition of lactation induced by treatment with still larger dosage (1 mg.) of diethylstilbestrol dipropionate both in intact and in ovariectomized rats was accompanied by marked loss of wt. of the mother and is interpreted as a toxic effect. Prepartal injn. of estrone does not prevent the initiation of lactation either in ovariectomized (25 [mu]g.) or in intact (25 [mu]g. and 100 [mu]g.) rats but does produce a delayed depression in intact animals. Daily treatment with progesterone begun prepartally (2.5 mg.) or postpartally (5. mg.) neither prevents nor inhibits lactation. Simultaneous injn. of estrone and progesterone begun prepartally or postpartally does not prevent lactation but it does inhibit established lactation after 10-12 days of treatment. The marked proliferation of the mammary glands showing inhibition of lactation suggests that stimulation of mammary growth by combined action of estrone and progesterone plays a role in the inhibition of milk secretion in the rat.