COMPARATIVE ENZYME-HISTOCHEMISTRY OF THE EARLY AND TERM RAT DECIDUA WITH SPECIAL ATTENTION TO DECIDUAL REGRESSION

As the early rat decidua is believed to fulfil functions other than th e late or basal decidua, the question as to whether this difference is reflected in decidual cell metabolism was investigated. Using cryosec tions of pregnant rat uteri of the 10th, 15th and 21st gestational day , activities of oxyradical-forming enzymes and hydrolases were. analys ed histochemically. The enzyme activities of decidual stromal cells an d fibroblasts of the metrial gland exhibited three main fluctuations. One group of enzyme activities did not change during gestation, a seco nd group decreased or disappeared, and a third group increased or was expressed in the late decidua only. Enzymes of the purine and polyamin e pathway, including oxyradical-forming oxidases, were absent from ear ly mesometrial decidual cells, but were highly active in the late regr essing decidua and metrial gland. Some acid hydrolases and neutral pro teases became active in the mature decidua. The possibility that purin e-degrading and oxyradical-forming enzymes support decidual as well as metrial gland regression, and thus placental separation, by direct ti ssue damage and/or by indirect rupture of lysosomal membranes, inducin g the release of acid hydrolases, is considered.