Effect of pregnancy and local effect of implantation on thymidine kinase and estrogen receptor in rat uterus (author's transl)

Abstract

We have previously reported that estradiol (E2) administration induces a particular isozyme of thymidine kinase (TK) in the uterus of immature rats but not of adult rats. This peculiar TK isozyme, which seems to be related to DNA synthesis in myometrial cells induced by E2 diminishes with the maturation of the rat. Growth with age and hypertrophy during pregnancy are similar phenomena from the standpoint of physiological uterine development. We are interested in the effect of pregnancy on TK activity and the cytoplasmic and nuclear estrogen receptor (ER) in the uterus. In the present study, an oviduct on one side was sectioned previous to mating, in order to compare TK and ER between the non-implanted and implanted uterine horns of the same rat during one to three weeks of pregnancy. No implantation was found in the uterine horn with the sectioned oviduct. In both the nonimplanted and implanted uterine horns, no increment of TK activity and no appearance of the specific TK isozyme were found during pregnancy. It seems that uterine growth with maturation is not similar to uterine hypertrophy during pregnancy. A local effect of E2 supplied by trophoblast is not evident in the level of TK. The cytoplasmic ER level of the nonimplanted horn was approximately twice that of the implanted horn. Unchanged levels of nuclear ER were shown in both uterine horns during pregnancy. The lower concentration of cytoplasmic ER in the implanted horn than in the nonimpalnted horn during pregnancy might be caused by the local effect of E2 supplied by trophoblast. These results indicated that uterine development during pregnancy might be caused by an enlargement of individual myometrial cells, and the local effect of steroids supplied by trophoblast might support ovum-implantation to the adjacent endometrium.