Uterine and Placental Growth: RNA and Protein Metabolism and Steroid Hormone Receptor Levels in the Endometrium, Whole Uterus and Cotyledons during Pregnancy in the Ewe

Abstract

Some aspects of uterine and placental growth have been examined during pregnancy in the ewe. Changes in in vitro rates of protein synthesis, RNA:DNA and protein:DNA ratios and the tissue concentration of DNA in intercaruncular endometrium and caruncles/cotyledons between days 0 (oestrus) and 112 of pregnancy were compared with corresponding changes in the concentrations of high-affinity cytosol receptors for oestradiol and progesterone in whole uterus and caruncles/maternal cotyledons. Rapid growth of the intercaruncular endometrium between days 28 and 112 and of the developing cotyledons between days 28 and 84 occur in the presence of tissue levels of both steroid receptors that are extremely low in relation to the corresponding levels seen in the uterus at oestrus. If uterine responses to steroid hormones are regulated by the amounts of specific receptor present in the tissue, the results support the concept that uterine growth after day 28 of pregnancy results primarily from the physical stimulus of the growing conceptus rather than from the actions of endogenous steroid sex hormones.

Growth of the endometrium and cotyledons during pregnancy in the ewe: rates of protein secretion and synthesis and nuclear and cytosol steroid hormone receptor levels

“…The present results for changes during pregnancy in RNA : DNA and protein : DNA ratios and in-vitro protein synthesis in intercaruncular and caruncular endometrium and fetal cotyledon agree well with our earlier findings (Miller & Stone, 1981). Changes in maternal cotyledon during days 56-112 were not previously examined.…”

“…a decrease from high oestrous levels to low levels similar to those previously described for whole uterus and caruncles/cotyledons (Miller & Stone, 1981). The active replenishment of cytosol progesterone receptor in rabbit uterus under conditions of chronic progesterone treatment (Isotalo, lsomaa & Jänne, 1981) and which would presumably be akin to the progesterone dominance of pregnancy, was not observed.…”

“…In a previous study changes in the in-vitro rates of protein synthesis and RNA : DNA and protein : DNA ratios in intercaruncular endometrium and fetal cotyledon during days 0-112 of pregnancy were compared with changes in the concentrations of high-affinity cytosol receptors for oestradiol and progesterone in whole uterus and maternal cotyledon. Rapid growth of these tissues between days 28 and 84 occurred in the presence of tissue levels of both cytosol steroid receptors that were extremely low in relation to the corresponding levels seen in the endometrium at oestrus (Miller & Stone, 1981). However, the interpretation of these data for cytosol receptors was made difficult by the absence of parallel data for nuclear oestradiol and progesterone receptor levels in these tissues.…”