As suggested by comparative studies done in various species, amino acid arylamidases (amino peptidases) may play a role in blastocyst implantation. 2. Histochemical studies of the guinea pig endometrium indicate that arylamidase increases in the stroma during pregnancy but is depleted in the vicinity of the blastocyst during implantation. 3. To further explore the possible significance of arylamidases in uterine function, endometrial arylamidase activity was measured in guinea pigs during the reproductive cycle, decidualization and after ovariectomy with and without estrogen (E) and/or progesterone (P) treatment. Arylamidase activity was maximal during pro-oestrus-oestrus (40.0 +/- 10.0 mu/mg protein). 4. Enzyme activity was markedly depleted in decidualized endometrial stroma (12.3 +/- 1.6, P less than 0.01); reduced by ovariectomy (20.5 +/- 2.7); and stimulated by E (29.2 +/- 1.2); P had little effect (21.9 +/- 3.5). 5. The physiological significance of modulation of endometrial arylamidase activity by steroid hormones is discussed.
