Abstract
It has been known that uterine tissue shows cyclic morphological changes in adult women. Such cyclic changes are closely related to secretion of steroid hormones from the ovary.
Last year, we reported on the mode of action of estrogen on the uterus.
In the present paper, we observed DNA Synthesis during proliferation induced by estradiol and secretory change by progesterone in the endometrium of rat uterus.
1) The time course of RNA and DNA synthesis following estradiol administration was observed. DNA synthesis reaches the maximum 24 hours after the treatment, while induction of RNA synthesis starts earlier than that of DNA and reaches its maximum level in 3 hours.
2) Thymidine kinase activity of the uterine tissue was measured after administration of estradiol. Estrogen caused an increase in the activity by about 4 times in comparison with that in the castrated control, and also administration of RNA preparation obtained from the rat uterus after estrogen treatment intensified both of DNA synthesis and thymidine kinase activity.
3) In the experiment of actinomycine S3 treatment prior to estrogen administration, any DNA synthesis in endometrium could not observed.
4) The administration of progesterone strongly inhibits DNA synthesis in the endometrium.
5) Puromycin at a level to inhibit protein synthesis induced a marked increase of DNA synthesis in the endometrium.
The results so far obtained sugest that estrogen first causes RNA synthesis followed by that of enzyme protein involved in DNA synthesis and progesterone displays a stimulatory effect to cell differentiation, therefore the rate of DNA synthesis was strongly inhibited. Furthermore, since puromycin accerates DNA synthesis, significance of protein in the regulatory action of DNA synthesis should be taken into account.
