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.