Endometrial Arylamidase Secretion: a Sensitive Parameter of Steroid Hormone Action and of Embryo- Maternal Interrelationships in the Rabbit

Amino acid arylamidase I (in earlier work also referred to as leucine aminop~ptidase) appears in the uterine epithelium and is extruded into the uterine lumen in considerable quantities after 3 d p.c. (days post coitum) in the rabbit. In the uterine secretion, the activity of this enzyme shows a very sharp and high peak at 5 d p.c., i .e. in the middle of the preimplantation phase, and it declines again rapidly until 8 d p.c. Preliminary experiments on the hormonal regulation indicate that arylamidase accumulates in the endometrium after progesterone treatment of no~-ovariectomized animals, while the significance of the minor increase seen after estradiol remains uncertain. Extrusion into the uterine lumen, on the other hand, is clearly progesterone-dependent. In fact, the sharp peak of activity in the uterine fluid at 5 days (including the steep increase before and the decline thereafter) can be mimicked by progesterone treatment of non-ovariectomized animals. Comparative investigations of pseudopregnant and pregnant uteri indicate that the blastocyst seems to stimulate, by an unknown signal, the extrusion of arylamidase I from the uterine epithelium into the uterine lumen. Since quantitative biochemical tests of aryl amidase activity are easy to perform, this enzyme may serve as a useful and particularly sensitive parameter of the action of steroid hormones, particularly of progesterone, on the endometrium.