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Placental lactogen (PL) has been measured throughout gestation by radioreceptor assay. Serum mouse PL (mPL) levels were low at the beginning of gestation, peaked at Day 10, and returned to low levels again by Day 13. From Day 13 until term, mPL levels remained low. No circadian rhythm in mPL levels was seen over two different 24 h periods. Mouse PL levels were correlated with the number of conceptuses in an animal from DayS 9 to 18 of gestation.
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Markoff et al. (1981) studied this question.
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