Oocyte interaction with progesterone

Not only do oocytes take up progesterone from the medium, but also they appear to retain a substantial proportion of the hormone (about 50%) for prolonged periods of time when incubated in hormone-free medium (Smith and Ecker, 1971). This bound steroid fraction was not competed out by the presence of a 100-fold excess of unlabeled progesterone. However, the additional observation that intracellular hormone could be coprecipitated with a protein extract (Smith and Ecker, 1971 see also Horton, 1969) led to the idea that this intracellular hormone might be responsible for the initiation of maturational events, possibly through interaction with a specific protein receptor. This appears not to be the case. 

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