Evidence of short-loop inhibition of decidual prolactin synthesis by decidual proteins. Part II.

We have recently demonstrated the suppression of decidual prolactin synthesis by decidual proteins accumulating in a dialysis membrane. In this report the reversibility of this suppression and the molecular weight range of the suppressor(s) are examined. Samples of 300 mg of decidua (n = 10) were cultured in three environments: in 30 ml of medium (control), in 3 ml of medium in a dialysis membrane suspended in 27 ml of medium, and in 2.7 ml of medium with 0.3 ml of concentrated decidual proteins of 10,000 to 35,000 molecular weight (giving a time 0 prolactin concentration of 220 ng/ml) in a dialysis membrane suspended in 27 ml of medium (n = 5) or in 2.7 ml of medium with 0.3 ml of concentrated decidual proteins greater than 35,000 molecular weight (giving a time 0 prolactin concentration of 5 ng/ml) in a dialysis membrane suspended in 27 ml of medium (n = 5). Dialysis membranes were discontinued at 48, 96, and 144 hours and the decidua within was subsequently cultured in 30 ml of medium until 240 hours. The suppression of prolactin synthesis identified previously was confirmed in this study. Further it was found that the suppression of decidual prolactin synthesis was reversed by the removal of decidua from the high decidual protein-prolactin environments of the dialysis membranes. Third, only the addition of decidual proteins between 10,000 and 35,000 molecular weight with a high prolactin concentration enhanced the suppression of new prolactin synthesis. We conclude that a decidual protein(s) between 10,000 and 35,000 molecular weight, possibly prolactin itself, is the primary control factor(s) in the modulation of prolactin synthesis in term decidua. Further the normal physiologic state of decidua is a high prolactin concentration in equilibrium with low prolactin synthesis. Therefore studies intended to assess the effects of modulators of prolactin synthesis in decidua should not be performed in low prolactin concentration-high prolactin synthesis conditions during short time periods (as has been the case in a majority of studies to date) since such conditions do not reflect normal physiologic conditions and may result in invalid conclusions.