Adrenomedullin and Its Receptor Components in the Porcine Uterus and Peri-implantation Conceptuses

Abstract

Abstract Adrenomedullin (ADM) is an evolutionarily conserved peptide hormone that regulates implantation, embryo spacing and placentation in humans and rodents. However, the potential roles of ADM in domestic animals, particularly pigs (as litter-bearing species), are not known. This study investigated expression patterns of ADM and its receptor components that include calcitonin receptor-like receptor (CALCRL), and receptor activity modifying protein (RAMP2) in porcine uteri and conceptuses (embryonic/fetus and its extra-embryonic membranes) during the peri-implantation period of pregnancy when 30–40% of embryonic death loss occurs. Gilts were observed for estrus and/or bred via artificial insemination at 12 and 24 h after onset of estrus (Day 0). On D 10, 11, 12, 13, 14, 15, or 16 of the estrous cycle and pregnancy (n=6 gilts per day and status), uteri were flushed with 20 ml sterile PBS (pH 7.2) after gilts were subjected to a midventral laparotomy. Pregnancy was confirmed by the presence of one or more morphologically normal conceptuses. Real-time quantitative RT-PCR analyses revealed that ADM mRNA in the endometrium was elevated for pregnant than for cyclic gilts between D 10 and 16 of pregnancy (day x status, P < 0.05). In cyclic gilts, endometrial ADM mRNA increased 9.0-fold (P < 0.05) between D 10 and 16; whereas it increased 58.1-fold (P < 0.01) in pregnant gilts between D 10 and 16. As ADM receptors, expression of mRNAs for CALCRL and RAMP2 also increased (P < 0.05) 13.4- and 5.5-fold, respectively, in the porcine conceptuses between D 10 and 16 of pregnancy. Further, ELISA analyses showed that total recoverable ADM in the uterine flushings was greater (status, P < 0.0001) for pregnant than for cyclic gilts in which ADM increased 173.8-fold (P < 0.0001) between D 10 and 16 of pregnancy. These results indicate that ADM may play functional roles in survival, growth and development of the porcine conceptus during the peri-implantation period of pregnancy.