RETINOL-BINDING PROTEIN GENE-EXPRESSION IN CYCLIC AND PREGNANT ENDOMETRIUM OF PIGS, SHEEP, AND CATTLE

Retinol-binding protein (RBP) is a major secretory product of conceptu ses and endometrium of the large domestic The present study examined t he abundance of RBP mRNA in cyclic and early pregnant endometrium of p igs, sheep, and cattle and confirmed the presence of RBP mRNA in perii mplantation conceptuses of the large domestic animals. Northern blot a nalysis, using porcine liver RBP cDNA as the probe, detected 2 1.0-1.1 -kb transcript in conceptuses and endometrium collected during the per iimplantation period of pregnancy in pigs (Day 15), sheep (Day 16), an d cows (Day 18). Slot-blot analysis of RBP mRNA in endometrium of pigs , sheep, and cows indicated differential RBP gene expression across da ys and statuses in pigs and sheep and across days alone in cows. In pi gs, RBP gene expression was low to undetectable at Days 0, 5, and 10 o f the estrous cycle and Day 10 of pregnancy. Levels of RBP mRNA increa sed (p < 0.06) from Days 10 to 12 and further (p < 0.001) to Day 15 ac ross both statuses. At Day 18, RBP mRNA levels decreased (p < 0.01) in cyclic pigs but remained elevated in endometrium of pregnant pigs. In sheep, levels of RBP mRNA increased between Days 10 and 12 and 14 in both cyclic and pregnant ewes; however, between Days 14 and 16, RBP mR NA levels remained elevated in cyclic endometrium but decreased (p < 0 .01) in endometrium of pregnant ewes. In a second experiment, RBP mRNA levels increased (p < 0.01) between Days 0-5 and Days 13-15 of the es trous cycle. RBP gene expression was similar in pregnant and cyclic ew es on Days 11 and 13, then increased in cyclic (p = 0.07) but not preg nant ewes, supporting results from experiment 1. Levels of RBP mRNA in creased in endometrium of both cyclic and pregnant cows between Days 1 0, 15, and 18; then cows, like sheep but unlike pigs, exhibited RBP mR NA at estrus (Day 0) and metestrus (Day 5). Results suggest differenti al RBP gene expression in endometrium of large domestic animals and su pport an important role for the vitamin A transport protein in uterine and conceptus physiology of early pregnancy.