Oestrogen-induced changes in the relative concentrations of ribonuclease and ribonuclease inhibitor in rat uterus

The cytoplasm of the immature rat uterus contains an excess of ribonuclease inhibitor over endogenous cytoplasmic ribonuclease. The ratio of free inhibitor to bound inhibitor is approximately 3:1. After treatment with oestrogen, there is a marked increase in the level of cytoplasmic ribonuclease such that the enzyme is present in excess of the inhibitor. The increase in activity appears to result from at least 2 distinct ribonucleases with molecular masses of approximately 14000 and 18000. The changes observed after oestrogen treatment are also evident during normal development of the rat uterus. The implications of these results on the proposed role of the inhibitor/ribonuclease system are discussed.