The effect of actinomycin D on the binding of tritiated oestradiol by the vagina of the ovariectomized mouse

The binding of [³H]oestradiol-17β by whole mouse vaginal tissue in vivo, and by subcellular fractions of mouse vaginal homogenates in vivo and in vitro, was examined at varying times after an intravaginal injection of the antimetabolite, actinomycin D. Under conditions of almost complete inhibition of protein synthesis the average receptor half-life was 24.2 ±3.2 hr, contrasting with the previously reported value of 5-6 days for the soluble oestrogen receptor of the rat uterus. The cytoplasm to nucleus transfer of the oestrogen receptor complex was inhibited by actinomycin D. No effect was observed on the sedimentation characteristics of the receptor and there was no indication of receptor subunit accumulation. Prolonged actinomycin D administration failed to abolish completely the oestrogen binding and there were indications that under these conditions the tissue was able partly to overcome the effects of the inhibitor.