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 time-course of cell hypertrophy and changes in in-vitro rates of secretion and synthesis of protein in intercaruncular and caruncular endometrium and maternal and fetal cotyledonary placenta have been examined during days 0-112 of pregnancy in the ewe. The concentrations of high-affinity receptors for oestradiol and progesterone in nuclear and cytosol fractions from these tissues were also determined. Protein secretion by intercaruncular endometrium increased 25-fold between days 0 and 84. On day 84 10(-5) M-colchicine blocked 75% of total secretion. Protein secretion did not increase in the other tissues. Protein synthesis and RNA:DNA ratio in intercaruncular endometrium increased steadily between days 0 and 112, whereas they did not change in caruncular endometrium between days 0 and 28 and declined in cotyledon between days 56 and 112. The levels of cytosol receptor for oestradiol and progesterone and of nuclear receptor for oestradiol in all tissues during days 56-112 were very low in relation to the corresponding levels in caruncular endometrium on day 0. The level of nuclear progesterone receptor in caruncular endometrium increased threefold between oestrus and day 28. The level of this receptor in cotyledon remained low on days 56-112, but in intercaruncular endometrium it increased to high values on days 84-112. The results demonstrated a major surge in secretory activity by the intercaruncular endometrium at around mid-gestation, which was associated with a marked increase in nuclear progesterone receptor levels but only a low level of nuclear oestradiol receptor. The observations do not suggest any important role for oestradiol or progesterone in the growth of fetal and maternal cotyledon.