Abstract
SUMMARY The incorporation of [3H]uridine into RNA in the blastocyst and uterus has been studied autoradiographically during delayed implantation and after treatment with oestrogen. Minimal RNA synthesis, as judged by the accumulation of perchloric acid-precipitable isotope originating from [3H]uridine, was seen in the blastocyst during delayed implantation. Treatment with oestrogen enhanced, within 5 min, incorporation of [3H]uridine in a number of cells in all regions of the blastocyst; there was a fourfold increase in the number of grains/cell and the uptake was predominantly located in the nucleus. The number of grains/cell in the blastocyst gradually increased from fourfold at 15 and sixfold at 30 min to a maximal tenfold increase at 60 min after treatment with oestrogen. Minimal RNA synthesis was seen in the uterus during delayed implantation. Treatment with oestrogen resulted, within 5 min, in a threefold increase in the number of labelled uterine epithelial cells and a sixfold increase in the number of grains/cell in the uterine epithelial nuclei; this level remained the same at 15, 30 and 60 min after hormone treatment. The significance of these results is discussed in relation to early action of oestrogen on the uterus and blastocyst. It is likely that activation of the delayed blastocyst may involve some mechanism which alters cell permeability.
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