THE OESTROGEN REQUIREMENT FOR IMPLANTATION AND THE EFFECT OF ITS DOSE ON THE IMPLANTATION RESPONSE IN THE MOUSE

Abstract

SUMMARY: It has been shown for the random-bred Swiss mouse that blastocyst implantation does not take place in the absence of oestrogen. Mated, ovariectomized mice receiving progesterone alone showed no evidence of implantation. However, if 17β-oestradiol benzoate (0·5 μg.) was administered in addition to progesterone, a high percentage of these animals had implantation sites and the response was not significantly different from that observed in control animals which were mated and either sham-operated or left surgically intact. The effect of the dose of oestradiol on the implantation response was also investigated. The combined data showed that the percentage of mice per group having implantation sites and the mean number of implantation sites per mouse increased as the dose of oestradiol was raised from 0·5 × 10⁻² μg. to 10⁻¹ μg. The implantation response declined as the dose of oestradiol was increased above 10⁻¹ μg. The median effective dose was found to be 2·91 × 10⁻² μg. with fiducial limits of error of 1·76 × 10⁻² μg. to 5·04 × 10⁻² μg.