Regulation of polyribosome formation and protein synthesis in the uterus. Effect of ovariectomy and administration of oestradiol-17β on the amino acid-incorporation activity in vitro and the cytoplasmic concentration in vivo of polyribosomal preparation

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Abstract
The hormonal regulation of cytoplasmic protein synthesis in the uterus is described. Polyribosomal preparation from uteri of normal or ovariectomized rats was isolated by procedure 3 and assayed for [14C]leucine-incorporation activity in the cell-free system, as described by Teng and Hamilton (1967). Ovariectomy of normal animals caused, 3 weeks after surgery, a 50-60% increase in the amino acid-incorporation activity in vitro of uterine polyribosomal preparation, but a 90-95% decrease in the cytoplasmic concentration in vivo of the preparation. Administration of 10ug of estradiol-17[beta] to ovariectomized rats at zero time caused, 10-12 hr. later, a 100% stimulation in amino acid-incorporation activity in vitro of the uterine polyribosomal preparation. From 12 hr. to 36 hr. after hormone administration, activity in vitro of the preparation decreased. If a 2nd dose of hormone was administered at 36 hr., the activity in vitro of the preparation continued to decrease, and approached at 48 hr. and 72 hr. the lower activity observed for the preparation from normal animals. The cytoplasmic concentration of polyribosomal preparation increased by 600-700% under these experimental conditions. If a 2nd dose of estradiol-17[beta] was not administered at 36 hr., the initially elevated cytoplasmic concentration of the preparation decreased by 50% from 36 hr. to 72 hr., and the activity in vitro of the preparation was not fully depressed to the ''normal'' value. Pretreatment of ovariectomized animals with actinomycin D or cycloheximide abolished 80-90% of the stimulatory effects of hormone treatment on the amino acid-incorporation activity in vitro and cytoplasmic concentration in vivo of uterine polyribosomal preparation. Two major conclusions are drawn from the results reported: that during early estrogen action new polyribosomes having amino acid-incorporation properties different from those of the old ones appear and accumulate in the cytoplasm of the uterus; and that the regulation of cytoplasmic protein synthesis in the organ by estrogen is of an indirect nature, with dual effects of the hormone on genetic transcription resulting in turn in a regulation of the rate and amount of genetic translation.