CHANGES OF OESTROGEN AND ITS RECEPTOR LEVELS DURING IMPLANTATION PERIOD IN PREGNENT RAT

LIU YIHSUN AND CHIA HSIAOCHIN(Department of Endocrinology, Institute of Zoology, Academia Sinica)  

Oestradiol-17β concentration in rat serum and uterus was measured by RIA. The serum concentration was found to be high on D_4 (65.68 pg/ml, p 0.05), and remarkably decreased to 38.65 pg/ml on D_5 (p0.05). The titre was increased again on D_6 (49.84 pg/ml).The uterine concentration of the oestrogen raised to a peak on D_3 (235.14 pg/g of wet tissue), and decreased to a much lower level on D_5 (147 pg/g of wet tissue, p0.05).The concentration of oestradiol receptors in rat uterine cytosol and nuclei was also measured during D_1 to D_7. The highest value of cytosol receptor (0. 576 pmole/mg of protein) was obtained on D_4 (calculation based on per unit of protein). After an unsignificant decrease on D_5 (0.455 pmole/mg of protein), it increased again on D_6. However, if the calculation was based on per unit DNA, the peak value was not found on D_4 but on D_6.The amount of nuclear receptor complex was high on D_4 (697 E_2 molecules/cell) and D_6 (607 E_2 molecules/cell), and fell on D_5 (p0.05, 352 E_2 molecules/cell).The results presented here indicate that the concentrations Of both oestradiol and its nuclear receptor show a peak On D_4. It is suggested that the increased oestrogen and its receptor of the uterus may be a prerequisite for implantation. The levels of oestrogen and its receptors in a majority of cases decreased significantly on D_5, the fact leads us to suggest that the oestrogen is presumably no longer necessary after having a priming effect for the uterus on D_4, It is possible that uterus may need a quiescent condition for the blastocysts to implant and develop.

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