Regulation of polyribosome formation and protein synthesis in the uterus. Effect of administration of graded doses of oestradiol-17β and actinomycin D on the amino acid-incorporation activity in vitro and the cytoplasmic concentration in vivo of polyribosomes

摘要

p1. The effects of graded doses of oestradiol-17β and actinomycin D, administered separately or together, on the amino acid-incorporation activity iin vitro/i and the cytoplasmic concentration iin vivo/i of uterine polyribosomes are described. Preparations of polyribosomes isolated from uteri of ovariectomized adult rats were determined for cytoplasmic concentration iin vivo/i and assayed for [sup14/supC]leucine-incorporation activity in the cell-free system, exactly as described by Teng & Hamilton (1967ib/i). 2. A minimal dose of 10μg of oestradiol-17β administered for 10h was found to increase, by about 100%, both the amino acid-incorporation activity iin vitro/i and the cytoplasmic concentration iin vivo/i of the polyribosomes. A minimal dose of 250μg of actinomycin D administered for 10h was found to inhibit, by about 50%, the incorporation activity iin vitro/i of the polyribosomes. All doses of the inhibitor administered for 10h failed to alter the cytoplasmic concentration iin vivo/i of the polyribosomes. 3. A dose of 10μg of oestradiol-17β restored to the control value the inhibitory effect of a dose of either 50 or 125μg of actinomycin D on the activity iin vitro/i of the polyribosomes, at 10h after treatment with the inhibitor and the hormone. In these experiments, there was an increase of 60–100% in the cytoplasmic concentration iin vivo/i of the polyribosomes. 4. A dose of 125μg of actinomycin D, administered to animals along with 10μg of oestradiol-17β for 6–36h, abolished the hormone-induced enhancement of the incorporation activity iin vitro/i, but did not prevent an increase of about 200% in the cytoplasmic concentration iin vivo/i of the polyribosomes. However, treatment with 750μg of the inhibitor abolished both stimulatory effects of the hormone. 5. The results reported indicate that the stimulatory effects of oestradiol-17β iin vivo/i on the number and activity of the cytoplasmic polyribosomes in the uterus of the ovariectomized rat have different sensitivities to actinomycin D, but the primary molecular mechanisms responsible for the results are unknown. The major conclusion drawn is that the formation and appearance in the cytoplasm of newly formed polyribosomes are important features of the early action of oestrogen in the uterus./p