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 the late or basal decidua, the question as to whether this difference is reflected in decidual cell metabolism was investigated. Using cryosections of pregnant rat uteri of the 10th, 15th and 21st gestational day, activities of oxyradical-forming enzymes and hydrolases were analysed histochemically. The enzyme activities of decidual stromal cells and fibroblasts of the metrial gland exhibited three main fluctuations. One group of enzyme activities did not change during gestation, a second group decreased or disappeared, and a third group increased or was expressed in the late decidua only. Enzymes of the purine and polyamine pathway, including oxyradical-forming oxidases, were absent from early mesometrial decidual cells, but were highly active in the late regressing decidua and metrial gland. Some acid hydrolases and neutral proteases became active in the mature decidua. The possibility that purine-degrading and oxyradical-forming enzymes support decidual as well as metrial gland regression, and thus placental separation, by direct tissue damage and/or by indirect rupture of lysosomal membranes, inducing the release of acid hydrolases, is considered.