Rate of Synthesis of Non-Ribosomal RNA in Castrate Uterus after Oestradiol-17β Stimulation

Abstract

OESTROGENS have been reported to stimulate preferentially the synthesis of ribosomal RNA in the castrate uterus^1–4. Thus it has been suggested that 50% or more of the RNA that is synthesized in the oestrogen-stimulated uterus is ribosomal precursor RNA^1,2,4. The concept is supported by the reports of enhanced ribosome formation during early oestrogen action^5,6. It has also been shown, however, that during the first 6 h after oestrogen administration there is no increase in total uterine RNA in the rat uterus^4,7 and also the castrate mouse uterus⁸. These findings seem to be incompatable with the idea that much of the RNA that is synthesized during this first 6 h is ribosomal precursor RNA, most of which accumulates as new stable rRNA. Determination of the absolute rates of total RNA synthesis in vivo should provide some insight into the amounts of various species of RNA that are synthesized after oestrogen administration. Data presented here for the rate of total RNA synthesis strongly suggest that all except a small portion of the RNA that is being synthesized at 4 h after oestrogen stimulation is unstable in vivo, and hence is not ribosomal precursor RNA.